Background: Satisfactory psychometric properties in offline questionnaires do not guarantee the same outcome in Web-based versions. Any construct that is measured online should be compared to a paper-based assessment so that the appropriateness of online questionnaire data can be tested. Little research has been done in this area regarding Attention-Deficit/Hyperactivity Disorder (ADHD) in adults.
Objective: The objective was to simultaneously collect paper-based and Web-based ADHD questionnaire data in adults not diagnosed with ADHD in order to compare the two data sources regarding their equivalence in raw scores, in measures of reliability, and in factorial structures.
Methods: Data from the German versions of the Connors Adult ADHD Rating Scales (CAARS-S), the Wender Utah Rating Scale (WURS-k), and the ADHD Self Rating Scale (ADHS-SB) were collected via online and paper questionnaires in a cross-sectional study with convenience sampling. We performed confirmatory factor analyses to examine the postulated factor structures in both groups separately and multiple group confirmatory factor analyses to test whether the postulated factor structures of the questionnaires were equivalent across groups. With Cronbach alpha, we investigated the internal consistency of the postulated factors in the different questionnaires. Mann-Whitney U tests with the effect size “Probability of Superiority (PS)” were used to compare absolute values in the questionnaires between the two groups.
Results: In the paper-based sample, there were 311 subjects (73.3% female); in the online sample, we reached 255 subjects (69% female). The paper-based sample had a mean age of 39.2 years (SD 18.6); the Web-based sample had a mean age of 30.4 years (SD 10.5) and had a higher educational background. The original four factor structure of the CAARS-S could be replicated in both samples, but factor loadings were different. The Web-based sample had significantly higher total scores on three scales. The five-factor structure of the German short form of the WURS-k could be replicated only in the Web-based sample. The Web-based sample had substantially higher total scores, and nearly 40% of the Web-based sample scored above the clinically relevant cut-off value. The three-factor structure of the ADHS-SB could be replicated in both samples, but factor loadings were different. Women in the Web-based sample had substantially higher total scores, and 30% of the Web-based sample scored above the clinically relevant cut-off value. Internal consistencies in all questionnaires were acceptable to high in both groups.
Conclusions: Data from the Web-based administration of ADHD questionnaires for adults should not be used for the extraction of population norms. Separate norms should be established for ADHD online questionnaires. General psychometric properties of ADHD questionnaires (factor structure, internal consistency) were largely unaffected by sampling bias. Extended validity studies of existing ADHD questionnaires should be performed by including subjects with a diagnosis of ADHD and by randomizing them to Web- or paper-based administration.
Satisfactory psychometric properties in offline questionnaires do not guarantee the same outcome in Web-based versions. Any construct that is measured online should be compared to a paper-based assessment so that the appropriateness of online questionnaire data can be tested . After analyzing common preconceptions about Internet questionnaires, Gosling et al [ ] conclude that the quality of online data is comparable to traditional paper-and-pencil methods. The authors argue that Internet samples are not representative of the general population, but that traditional methods also do not achieve this. Web-based questionnaires are even considered to be more feasible in order to collect data in large population-based epidemiological studies [ ].
Several studies did not find substantial differences between Web-based and paper-based modes of administration [- ]. They were able to show similar psychometric properties or identical factor structures [ - ]. Those latter studies did not use clinical questionnaires to assess psychopathology, but no significant differences were found when depression questionnaires were administered in paper and online versions among the same individuals [ ]. Comparable results regarding psychometric properties and absolute differences in Internet versus paper-and-pencil administration of several panic and agoraphobia questionnaires were found by Carlbring et al [ ]. Both studies included pre-selected or self-recruited patient groups applying for treatment. A Web Screening Questionnaire for mental disorders yielded a high number of false positives though [ ], while others reported satisfactory diagnostic accuracy in the Web-based detection of depressive disorders [ ].
Buchanan  is skeptical of using Web-based questionnaires for normative comparisons, especially in clinical psychology. Several studies showed that score distributions between paper and online administration differed, with higher scores in Internet samples [ ]. He therefore argued not to compare online questionnaire data to established norms.
Attention-Deficit/Hyperactivity Disorder (ADHD), with its core symptoms of inattention, hyperactivity, and impulsivity, is listed under disorders usually first diagnosed in childhood or adolescence in DSM-IV and ICD-10. It was shown that ADHD often persists into adulthood with prevalence rates between 4 to 5% [- ]. We found only two studies in which measurement of ADHD via Web-based versions was examined. Steenhuis et al [ ] applied a within-subject design to administer the ADHD section of the Diagnostic Interview Schedule for Children (DISC-IV) to parents. Intraclass correlation coefficients ranged between .87 and .94. A qualitative study examined acceptability of the Web-based version of the ADHD rating scale T-SKAMP in 19 teachers [ ]. A large majority of teachers preferred the Web-based version over a paper version. They perceived it to be easier, shorter, simpler, and more informative, time saving, and flexible. Communication between teachers and physicians might be improved with this tool. No further ADHD diagnostic instruments, such as the SNAP and SWAN Scale for children [ ] or common adult ADHD assessment instruments (see [ ] for a review) were implemented as Web-based versions.
The Conners Adult ADHD Rating Scales (CAARS)  had satisfactory psychometric properties in their German translation [ - ] and were found to have the same factor structure as the American original, enabling them to be used for cross-cultural research. The aim of our study was to simultaneously collect paper-based and Web-based CAARS questionnaire data together with two other established ADHD questionnaires available in German and to compare the two data sources by different statistical measures regarding their equivalence in raw scores, measures of reliability, and factorial structures. To do so, we intended to collect normative data online and via paper questionnaires from subjects without a diagnosis of ADHD in order to examine whether online normative data can be merged with data from paper questionnaires.
We conducted a cross-sectional study on German adults with no serious chronic disease, who were over 18 years of age and without a lifetime diagnosis of ADHD. Participants in the paper-based sample were recruited by convenience sampling (university students, people from apprentice institutions, local neighborhoods, waiting areas such as airports, hairdressers, primary care physicians, and colleagues). Subjects were provided with a short study description and asked to complete the CAARS self-report (CAARS-S) as well as the German version of the Wender Utah Rating Scale (WURS-k), the German ADHD Self Rating Scale (ADHS-SB), and questions on age, gender, and education level. We disseminated approximately 500 printed questionnaires.
The Web-based questionnaire was also a cross-sectional convenience sample. We advertised for the online study on the websites of the Departments of General Practice/Family Medicine and Clinical Psychology at Philipps University Marburg and on a special Facebook page created exclusively for our study. Additionally, flyers with the online address of the Web-based questionnaire were distributed in the same recruitment areas as the paper-based questionnaires. For informed consent in the online study, the homepage prompted subjects to open a file with the study information and to check a box agreeing to participate in the study. Without checking this box, further pages of the questionnaire were not accessible. Since the survey was voluntary, all subjects had the ability to discontinue completing the questionnaire at any time. Subjects could see their progress in completing the questionnaire via a small progress bar on the upper right side of the screen. On average, subjects needed 15:34 minutes to complete the survey; the majority of participants completed the survey during the afternoon (hour 15, or 3 p.m.). At the end of the questionnaire, subjects had the opportunity to receive feedback on their responses. This indicated whether their scores were within the normal range or higher. In cases of the latter, no diagnosis was offered, but it was suggested to seek professional assessment. Data protection was insured in that only the principal investigator (HC) had access to the unipark page  that generated and stored the data. Additionally, no personal information was requested of the subjects.
For development and testing, the paper versions of the questionnaires were entered into unipark. The research team and then students were asked to test this online version. The link was activated after testing for functionality and usability.
The survey was online from July 12, 2010, to August 30, 2011. On average, the page was accessed 26.16 times per week (view rate), though only 6.69 (25 %) subjects per week completed the survey (completion rate). Cookies were used to assign a unique user identifier to each client computer and were set on the first page. A session was valid for a total of 120 minutes.
The items were presented in the same order as the paper-and-pencil questionnaires, but only an average of six items were displayed per page (see). When subjects did not complete all items on a page, they were asked to fill in the missing items in order to activate the “next” button. Therefore, no missing data could result in the online sample. Subjects were always able to review and change their answers with a “back” button. If subjects decided not to complete an answer, they could stop the survey. The majority of participants (57.44 %) discontinued filling out the survey on the first page.
For analyses, only questionnaires where subjects indicated they had not received a lifetime diagnosis of ADHD were analyzed. Apart from replacing missing items in paper versions with the expectation-maximization or the multiple imputation algorithms, no statistical corrections were performed.
Our study conforms to the Declaration of Helsinki and was approved by the local ethics committee of the Faculty of Medicine at the Philipps University in Marburg, Germany.
Connors Adult ADHD Rating Scales
The German version of the CAARS-S assesses ADHD symptoms in adults aged 18 years or older. Symptoms are rated on a Likert-type scale (0 = not at all/never to 3 = very much/very frequently). The long version consists of 66 items, but only 42 items were included in the original factor analysis by Conners et al  due to statistical restrictions made by the authors. Four factors emerged from their analyses: inattention/memory problems, hyperactivity/restlessness, impulsivity/emotional ability, and problems with self-concept. Confirmatory factor analyses of the German version in healthy adults and ADHD patients supported this factor analytic solution [ , ]. The four subscales were significantly influenced by age, gender, and the number of years in education. Symptom severity decreased with increasing age, males scored higher than females on hyperactivity and sensation-seeking behavior, and females scored higher than males on problems with self-concept. Overall symptom ratings were higher for individuals who had received less education. Test-retest reliability ranged between .85 and .92; sensitivity and specificity were high for all four subscales. The CAARS-S represents a reliable and cross-culturally valid measure of current ADHD symptoms in adults [ ].
Wender Utah Rating Scale
The German version of the Wender Utah Rating Scale (WURS-k) [, ] retrospectively assesses ADHD-relevant childhood behaviors and symptoms in adults. It consists of 25 items that distinguished patients with ADHD from a nonpatient comparison group. Subjects are instructed to rate 25 items that complete sentence stems such as ‘‘As a child I was or had...’’. Ratings are to be completed on a 5-point Likert scale (0 =not at all or very slightly to 4=very much). Test-retest reliability and Cronbach alpha were around .90. Factor analyses generated a 5-factor solution with the factors inattention/hyperactivity, impulsivity, anxiety/depression, oppositional behavior, and social adaptation by using 21 items. A total score >29 points hints at the possibility of ADHD during childhood.
ADHD Self Rating Scale
The German ADHD Self Rating Scale (ADHS-SB) consists of the 18 DSM-IV items that are broken down into the factors “inattention” (9 items), “hyperactivity”, and “impulsivity” (9 items together) . The items are scored on a 4-point Likert scale (0=not at all to 3=very pronounced/almost always the case). Test-retest reliability coefficients were between .78 and .89. Correlations with subscales of the NEO Five Factor Inventory were in the expected directions. A total score >17 points hints at the possibility of adult ADHD.
We performed confirmatory factor analyses to examine the postulated factor structures in both groups separately and multiple group confirmatory factor analyses using AMOS 19 to test whether the postulated factor structures of the questionnaires were equivalent across the groups. The factors were allowed to correlate because this is theoretically plausible in all three questionnaires. We used unweighted least squares as this estimation method makes no distributional assumptions .
Using multiple group analysis, we examined several levels of invariance between the groups. Configural invariance as the lowest level of invariance exists when the structure of the factor loading matrices is identical in all groups. Metric invariance occurs when factor loadings are identical in all groups. Scale invariance means that the measurement intercepts are the same across groups. Invariance of measurement errors exists if the error variables of measurement models, factor covariances, and factor variances are identical across groups.
We calculated several model fit indices to evaluate the results of our analyses. The root mean square residual (RMR) measures the mean absolute value of the covariance residuals . Values less than .05 indicate a good model fit [ ], but other authors state that a value of less than .10 signals an acceptable model fit [ - ]. The standardized root mean square residual (SRMR) eliminates scaling effects of the RMR. Values ≤ .10 indicate a good model fit [ ]. The Global Fit Index (GFI) can measure the proportion of variance and covariance that a given model is able to explain. A GFI equal or higher than .90 can be considered as reflecting a good model fit [ ]. The adjusted global fit index (AGFI) takes the number of parameters used in computing the GFI into account. An AGFI equal or higher than .90 can be considered as showing a good model fit [ ]. These fit indices were calculated for each of the aforementioned invariance levels. Differences of fit indices between these invariance levels should not be larger than .01 [ ], otherwise the criteria for a higher invariance level are not reached.
With Cronbach alpha, we investigated the internal consistency of the postulated factors in the different questionnaires. Values >.70 are considered to be acceptable .
Huber’s M estimators were calculated when standard deviation values were close to their respective means, signaling high variance .
Mann-Whitney U tests were used to compare absolute values in the questionnaires between the two groups. The effect size “Probability of Superiority (PS)”, PS=U/(n1*n2), indicates the probability that a randomly selected subject of group n1 has a higher score than a randomly selected subject of group n2. A PS of .50 means that both groups are equal regarding a specific variable, and that there is no effect. Consequently, the larger the effect, the more PS deviates from .50 .
The alpha level for statistical significance was set at .05 (two-sided). Missing responses in the paper versions were replaced using the expectation-maximization or the multiple imputation algorithms [- ].
In the paper-based sample, we received responses from 328 participants of which 6 indicated they were diagnosed with ADHD, and 11 did not answer this question. Therefore, a total sample of 311 subjects resulted, meaning that 65.6% of our 500 printed questionnaires were returned. This cannot be regarded as a return rate as we did not record those subjects who were personally asked and refused to participate. In the Web-based sample, we received responses from 273 participants of which 18 indicated that they were diagnosed with ADHD so that a total sample of 255 subjects resulted. The flow of subjects in our study samples is depicted in. shows the demographic characteristics of the two samples.
|Paper-based (n=311)||Web-based (n=255)|
|Female||228 (73.3%)||176 (69.0%)|
|Male||83 (26.7%)||79 (31.0%)|
|Age, mean years (SD)||39.2 (18.6)||30.4 (10.5)|
|University||61 (19.7%)||73 (28.6%)|
|Apprenticeship||86 (27.7%)||35 (13.7%)|
|High school||66 (21.3%)||130 (51.0%)|
|Middle school||61 (19.7%)||15 (5.9%)|
|Basic school||36 (11.6%)||2 (0.8%)|
The samples did not differ with respect to gender (χ2 test: P=.26, Cramer V=.05). The Web-based sample was, on average, younger than the paper-based sample. This difference was statistically significant with a rather moderate effect size (Mann-Whitney U test: P<.001, PS = .41). In the Web-based sample, there were more participants with a university degree and more subjects attending high school, while in the paper-based sample, there were more participants attending middle or basic school or with a completed apprenticeship. This difference was statistically significant with a high effect size (χ2 test: P<.001, Cramer V=.42).
Connors Adult ADHD Rating Scales
There was a maximum of 9% missing values on single variables in the paper sample; these were missing completely at random (Little’s MCAR test, P=.27). They were replaced with the expectation maximization (EM) algorithm .
The four-factor model (df = 813) was supported in both groups. In the paper-based sample, the standardized RMR was .08, the RMR was .04, the GFI was .93, and the AGFI was .92. In the Web-based sample, the standardized RMR was .07, the RMR was .05, the GFI was .98, and the AGFI was .97. These fit indices signal a good model fit.lists the correlations of CAARS items (loadings) with their postulated factors.
Except for Item 3 (“I don’t plan ahead”) of the factor “inattention/memory”, Items 1 (“I like to be doing active things”) and 5 (“I am a risk-taker or a daredevil”) of the hyperactivity factor, and Item 43 (“I step on people’s toes without meaning to”) on the impulsivity factor, all other items have loadings > .40 in both samples.
The intercorrelations between the factors are consistently higher in the Web-based sample. The largest differences between the two groups were found in correlations involving “self-concept” (see).
Multiple group analysis revealed that the factor structures were the same in both samples, signaling configural invariance (SRMR=.04, RMR=.04, GFI=.99, AGFI=.99). However, factor loadings were different (SRMR=.06, RMR=.10, GFI=.97, AGFI=.97) because all model fit indices increased > .01 when testing metric invariance. Consequently, other invariance assumptions were also not supported.
Cronbach alpha of the subscales ranged from .81 to .85 in the paper-based sample and from .89 to .91 in the Web-based sample.
Absolute subscale differences between the two groups were all significant with the Web-based sample scoring substantially higher with pronounced effect sizes (). For example, the probability that a randomly chosen subject from the paper-based sample has a higher inattention/memory score than a randomly chosen subject from the Web-based sample is .35.
As there is no normative data for Germany to date, we applied strict cut-off values based on American normative data T-value of 65, 94th percentile). The cut-off for “inattention/memory” was > 22 points; “hyperactivity” > 26 points; “impulsivity” > 22 points; and “self-concept” > 13 points. Regarding the total score of “inattention/memory”, 27 subjects (10.6%) in the Web-based sample scored above this value while 4 (1.3%) did so in the paper-based sample. This difference was significant with a moderate effect size (χ2 test: P<.001, Cramer V=.20). Regarding the total score of “hyperactivity”, 5 subjects (2.0%) in the Web-based sample scored above this value while 2 (0.6%) did so in the paper-based sample. This difference was not significant (χ2 test: P=.16, Cramer V=.06). Regarding the total score of “impulsivity”, 20 subjects (7.8%) in the Web-based sample scored above this value while 6 (1.9%) did so in the paper-based sample. This difference was significant with a small effect size (χ2 test: P=.001, Cramer V=.14). Regarding the total score of “self-concept”, 30 (11.8%) in the Web-based sample scored above this value while 13 (4.2%) did so in the paper-based sample. This difference was significant with a small effect size (χ2 test: P=.001, Cramer V=.14).
Wender Utah Rating Scale (Short Form)
There was a maximum of 2% missing values on single variables in the paper sample that were missing completely at random (Little’s MCAR test, P=.57). These were replaced with the EM algorithm . Due to technical difficulties, WURS-k data of 11 participants in the Web-based sample were not available, resulting in n=244.
The model in the paper-based sample was not admissible because the covariance matrix between the postulated five factors was not positive definite. This leads to the conclusion that the model is wrong , and it was thus rejected.
In the Web-based sample, the model (df = 179) was supported: SRMR = .07, RMR = .09, GFI = .98, AGFI = .97.depicts the loadings on the postulated factors.
As shown in, except for Item 23 (problems with police) on the factor “social adaptation”, all other items have high loadings > .4 on their postulated factors. The factors “inattention” and “impulsivity” correlated highest in the Web-based sample (r=.79), followed by “inattention” and “anxiety/depression” (r=.73), “impulsivity” and “oppositional behavior” (r=.72), and “inattention” and “oppositional behavior” (r=.72) ( ).
Due to the rejected model in the paper-based group, no multiple group analysis could be calculated.
Cronbach alpha of the subscales ranged from .68 to .82 in the paper-based sample and from .79 to .89 in the Web-based sample. No coefficients were calculated for the subscale “social adaptation” as it consists of only two items.
Absolute values of the total score were significantly higher (Mann-Whitney U test: P<.001; PS = .09) in the Web-based sample (mean 28.6, SD 14.0; Huber’s M estimator 26.2) than in the paper-based sample (mean 11.0, SD 6.8; Huber’s M estimator 9.6).
After applying the recommended cut-off value for the total score (> 29 points) [, ], 38.1% in the Web-based sample scored above this value while merely 2.5% did so in the paper-based sample. This difference was significant with a high effect size (χ2 test: P<.001, Cramer V=.46).
ADHD Self Rating Scale
There was a maximum of 1.3% missing values on single variables in the paper sample, except for Item 4 that asks for difficulties in the field of work. Student participants in the paper version did not complete this item, so 28.5% of missing at random data resulted. These were replaced with the multiple imputation algorithm by five imputations. The following calculations were done separately for the five imputations, and the respective results were averaged. Enders  recommends a larger number of imputations, but results showed only marginal differences between imputed datasets.
The four-factor model (df = 132) was supported in both groups. In the paper-based sample, the standardized RMR was .06, the RMR was .06, the GFI was .97, and the AGFI was .96. In the Web-based sample, the standardized RMR was .06, the RMR was .04, the GFI was .98, and the AGFI was .98. These fit indices signal a good model fit.lists the loadings of ADHS-SB items on their postulated factors.
As shown in, except for Item 6 (avoidance of tasks with mental load) on the factor “inattention”, and Item 14 (feel like driven by a motor) on the factor “hyperactivity”, both in the paper-based sample, all other items have high loadings >.4 on their postulated factors.
The correlation between the factors inattention and hyperactivity is significantly higher in the paper-based sample, while the intercorrelations between the other factors are higher in the Web-based sample ().
Multiple group analysis revealed that the factor structures were the same in both samples, signaling configural invariance (SRMR = .06, RMR = .03, GFI = .98, AGFI = .98). However, factor loadings were different (SRMR = .15, RMR = .08, GFI = .83, AGFI = .79) because all model fit indices increased > .01 when testing metric invariance. Consequently, other invariance assumptions were also not supported.
Cronbach alpha of the subscales ranged from .60 to .83 in the paper-based sample and from .79 to .91 in the Web-based sample.
Absolute differences between the two groups were significant with the Web-based sample (mean 12.8, SD 9.1; Huber’s M estimator 11.1) scoring substantially higher than the paper-based sample (mean 2.2, SD 3.0; Huber’s M estimator 1.4) with a high effect size (Mann-Whitney U test: P<.001, PS = .08).
After applying the recommended cut-off value for the total score (> 17 points) , 30% in the Web-based sample scored above this value, while only 0.6% did so in the paper-based sample. This difference was significant with a large effect size (χ2 test: P<.001, Cramer V=.42).
|Paper-based||Web-based||Mann-Whitney U Test (P) & effect size (PSb)|
|Inattention/Memory||8.6 (SD 4.8)|
Huber’s Ma 8.2
|12.3 (SD 7.1) |
Huber’s M 11.2
|Hyperactivity||9.0 (SD 5.3) Huber’s M 8.0||11.2 (SD 6.1) Huber’s M 10.3||<.001; PS=.38|
|Impulsivity||9.4 (SD 5.2) Huber’s M 8.8||12.3 (SD 6.6) Huber’s M 11.5||<.001; PS=.37|
|Self-concept||5.6 (SD 3.6) Huber’s M 5.1||7.5 (SD 4.3) Huber’s M 7.1||<.001; PS=.37|
aHuber’s M estimator.
bPS = probability of superiority.
|Oppositional behavior||<-->||Social adaptation||.58|
We compared Web-based and paper-based administrations of three ADHD questionnaires for adults. Subjects in the online sample were older and had a higher educational background. The original four-factor structure of the Conners Adult ADHD Rating Scales could be replicated in both samples, but factor loadings were different. Internal consistencies were high in both groups, but the Web-based sample had significantly higher total scores in three subscales with 7.8 to 11.8% above clinically relevant cut-off values, compared to 1.3 to 4.2% in the paper-based sample. The five-factor structure of the German short form of the Wender Utah Rating Scale could be replicated only in the Web-based sample. Internal consistencies were acceptable to high in both groups. The Web-based sample had substantially higher total scores and nearly 40% of the Web-based sample scored above the clinically relevant cut-off value. The three-factor structure of the ADHD Self Rating Scale could be replicated in both samples, but factor loadings were different. Internal consistencies were acceptable to high in both groups. The Web-based sample had substantially higher total scores, and 30% of the Web-based sample scored above the clinically relevant cut-off value. Therefore, psychometric properties were similar in both samples, but the Web-based sample had substantially higher scores on all three questionnaires.
The relatively high dropout rate in our Web-based sample is also reported in the literature. Additional informed consent procedures were shown to increase early dropout in Web-based studies . Kongsved et al [ ] administered paper and online questionnaires to women referred for mammography; their questionnaires were comparable in length to our study. In their study, the Internet version had a higher completeness of data but a lower response rate. A lower response rate was also found in surgeons responding to an online questionnaire [ ]. We cannot compare dropout rates in our samples because we did not record those who were personally asked and refused to participate in the paper-based sample.
Demographic differences (younger age, higher education) might have influenced the results . ADHD is a disorder with a higher prevalence for men. Our predominantly female samples in both versions are therefore not suitable for deriving normative data. Women tend to participate more in psychological studies. The gender distributions in our study are quite comparable to common sample characteristics regarding online study participation [ , ]. Subjects in the Internet sample might have experienced psychological distress regarding ADHD symptoms so that they saw their participation in the context of assessing themselves for the disorder. One also has to consider that the probability that subjects in a certain geographic region have a high prevalence of ADHD symptoms in paper-based questionnaires is much lower than the probability of reaching such individuals via the Internet without any geographic barriers. On the other hand, an increased self-disclosure might also be an important factor. Subjects might have considered the completion of online questionnaires to be more anonymous than giving away hand-written information, since participants in an online study reported lower social anxiety and lower social desirability than those in the paper-based group [ ].
Our results contradict the conclusion of Gosling et al  that subjects in Internet samples are not unusually maladjusted. It clearly depends on the context of the study. Even when the intention is to collect normative data for clinical questionnaires, one has to consider that the scores of online samples can be inflated [ ].
On the other hand, our results corroborate the assumption of Rhodes et al  that previously hidden subgroups can be reached by Internet research. This might also be true for other medical disorders [ ]. Whether our subgroup of women with higher scores on ADHD questionnaires has clinical significance must be determined by future studies with more controlled recruitment strategies.
Several limitations have to be mentioned. We did not randomize subjects to online and paper versions, so differences between the two groups might have arisen by sampling biases and should be replicated under randomized conditions. Different recruitment strategies for the paper and online samples might have influenced the results. Although relatively high discontinuation rates are common in online research, they might have caused bias in the results. In future online studies, leaving out questions should also be possible to create conditions similar to paper administration.
Data from the Web-based administration of ADHD questionnaires for adults should not be used for the extraction of population norms. Separate norms should be established for ADHD online questionnaires. General psychometric properties of ADHD questionnaires (factor structure, internal consistency) were largely unaffected by sampling bias. Extended validity studies of existing ADHD questionnaires should be performed by including subjects with a diagnosis of ADHD and by randomizing them to Web- or paper-based administration.
This study received no financial grants.
Conflicts of Interest
- Strickland OL, Moloney MF, Dietrich AS, Myerburg S, Cotsonis GA, Johnson RV. Measurement issues related to data collection on the World Wide Web. ANS Adv Nurs Sci 2003;26(4):246-256. [Medline]
- Gosling SD, Vazire S, Srivastava S, John OP. Should we trust Web-based studies? A comparative analysis of six preconceptions about internet questionnaires. Am Psychol 2004 Mar;59(2):93-104. [CrossRef] [Medline]
- Ekman A, Dickman PW, Klint A, Weiderpass E, Litton JE. Feasibility of using Web-based questionnaires in large population-based epidemiological studies. Eur J Epidemiol 2006;21(2):103-111. [CrossRef] [Medline]
- Ritter P, Lorig K, Laurent D, Matthews K. Internet versus mailed questionnaires: a randomized comparison. J Med Internet Res 2004 Sep 15;6(3):e29 [FREE Full text] [CrossRef] [Medline]
- Van De Looij-Jansen PM, De Wilde EJ. Comparison of Web-based versus paper-and-pencil self-administered questionnaire: effects on health indicators in Dutch adolescents. Health Serv Res 2008 Oct;43(5 Pt 1):1708-1721 [FREE Full text] [CrossRef] [Medline]
- Denscombe M. Web-based questionnaires and the mode effect. Social Science Computer Review 2006;24(2):246-254. [CrossRef]
- Hardré PL, Crowson HM, Xie K, Ly C. Testing differential effects of computer-based, Web-based and paper-based administration of questionnaire research instruments. Br J Educ Technol 2007 Jan 2007;38(1):5-22. [CrossRef]
- Vallejo MA, Jordán CM, Díaz MI, Comeche MI, Ortega J. Psychological assessment via the internet: a reliability and validity study of online (vs paper-and-pencil) versions of the General Health Questionnaire-28 (GHQ-28) and the Symptoms Check-List-90-Revised (SCL-90-R). J Med Internet Res 2007;9(1):e2 [FREE Full text] [CrossRef] [Medline]
- Hardré PL, Crowson HM, Xie K. Differential Effects of Web-Based and Paper-Based Administration of Questionnaire Research Instruments in Authentic Contexts-of-Use. Journal of Educational Computing Research 2010 Jan 2010;42(1):103-133. [CrossRef]
- Riva G, Teruzzi T, Anolli L. The use of the internet in psychological research: comparison of online and offline questionnaires. Cyberpsychol Behav 2003 Feb;6(1):73-80. [CrossRef] [Medline]
- Holländare F, Andersson G, Engström I. A comparison of psychometric properties between internet and paper versions of two depression instruments (BDI-II and MADRS-S) administered to clinic patients. J Med Internet Res 2010;12(5):e49 [FREE Full text] [CrossRef] [Medline]
- Carlbring P, Brunt S, Bohman S, Austin D, Richards J, Öst L, et al. Internet vs. paper and pencil administration of questionnaires commonly used in panic/agoraphobia research. Computers in Human Behavior 2007 May 2007;23(3):1421-1434. [CrossRef]
- Donker T, van Straten A, Marks I, Cuijpers P. A brief Web-based screening questionnaire for common mental disorders: development and validation. J Med Internet Res 2009;11(3):e19 [FREE Full text] [CrossRef] [Medline]
- Lin CC, Bai YM, Liu CY, Hsiao MC, Chen JY, Tsai SJ, et al. Web-based tools can be used reliably to detect patients with major depressive disorder and subsyndromal depressive symptoms. BMC Psychiatry 2007;7:12 [FREE Full text] [CrossRef] [Medline]
- Buchanan T. Internet-based questionnaire assessment: appropriate use in clinical contexts. Cogn Behav Ther 2003;32(3):100-109. [CrossRef] [Medline]
- Whitehead L. Methodological issues in Internet-mediated research: a randomized comparison of internet versus mailed questionnaires. J Med Internet Res 2011;13(4):e109 [FREE Full text] [CrossRef] [Medline]
- Davidson MA. ADHD in adults: a review of the literature. J Atten Disord 2008 May;11(6):628-641. [CrossRef] [Medline]
- Ramsay JR, Rostain AL. Adult ADHD research: current status and future directions. J Atten Disord 2008 May;11(6):624-627. [CrossRef] [Medline]
- Weiss M, Murray C. Assessment and management of attention-deficit hyperactivity disorder in adults. CMAJ 2003 Mar 18;168(6):715-722 [FREE Full text] [Medline]
- Steenhuis MP, Serra M, Minderaa RB, Hartman CA. An Internet version of the Diagnostic Interview Schedule for Children (DISC-IV): correspondence of the ADHD section with the paper-and-pencil version. Psychol Assess 2009 Jun;21(2):231-234. [CrossRef] [Medline]
- Bhatara VS, Vogt HB, Patrick S, Doniparthi L, Ellis R. Acceptability of a Web-based attention-deficit/hyperactivity disorder scale (T-SKAMP) by teachers: a pilot study. J Am Board Fam Med 2006;19(2):195-200 [FREE Full text] [Medline]
- Swanson JM, Schuck S, Mann-Porter M, Carlson C, Hartman CA, Sergeant JA, et al. Categorical and Dimensional Definitions and Evaluations of Symptoms of ADHD: History of the SNAP and the SWAN Rating Scales. The International Journal of Educational and Psychological Assessment 2012;10:51-70.
- Rösler M, Retz W, Stieglitz RD. Psychopathological rating scales as efficacy parameters in adult ADHD treatment investigations - benchmarking instruments for international multicentre trials. Pharmacopsychiatry 2010 May;43(3):92-98. [CrossRef] [Medline]
- Conners CK, Erhardt D, Sparrow E. Conner´s Adult ADHD Rating Scales (CAARS). Technical manual. North Tonawanda, NY: Multi-Health Systems; 1999.
- Christiansen H, Hirsch O, Philipsen A, Oades RD, Matthies S, Hebebrand J, et al. German Validation of the Conners Adult ADHD Rating Scale-Self-Report: Confirmation of Factor Structure in a Large Sample of Participants With ADHD. J Atten Disord 2012 Mar 21. [CrossRef] [Medline]
- Christiansen H, Kis B, Hirsch O, Matthies S, Hebebrand J, Uekermann J, et al. German validation of the Conners Adult ADHD Rating Scales (CAARS) II: reliability, validity, diagnostic sensitivity and specificity. Eur Psychiatry 2012 Jul;27(5):321-328. [CrossRef] [Medline]
- Christiansen H, Kis B, Hirsch O, Philipsen A, Henneck M, Panczuk A, et al. German validation of the Conners Adult ADHD Rating Scales-self-report (CAARS-S) I: factor structure and normative data. Eur Psychiatry 2011 Mar;26(2):100-107. [CrossRef] [Medline]
- Unipark. URL: http://www.unipark.info/1-0-online-befragungssoftware-fuer-studenten-und-universitaeten-unipark-home.htm [accessed 2013-02-19] [WebCite Cache]
- Retz-Junginger P, Retz W, Blocher D, Weijers HG, Trott GE, Wender PH, et al. [Wender Utah rating scale. The short-version for the assessment of the attention-deficit hyperactivity disorder in adults]. Nervenarzt 2002 Sep;73(9):830-838. [CrossRef] [Medline]
- Retz-Junginger P, Retz W, Blocher D, Stieglitz RD, Georg T, Supprian T, et al. [Reliability and validity of the Wender-Utah-Rating-Scale short form. Retrospective assessment of symptoms for attention deficit/hyperactivity disorder]. Nervenarzt 2003 Nov;74(11):987-993. [CrossRef] [Medline]
- Rösler M, Retz W, Retz-Junginger P, Thome J, Supprian T, Nissen T, et al. [Tools for the diagnosis of attention-deficit/hyperactivity disorder in adults. Self-rating behaviour questionnaire and diagnostic checklist]. Nervenarzt 2004 Sep;75(9):888-895. [CrossRef] [Medline]
- Blunch N. Introduction to structural equation modeling using SPSS and AMOS. London: Sage; 2008.
- Kline RB. Principles and practice of structural equation modeling. New York: Guilford; 2005.
- Arbuckle JL. Amos 17.0 User´s Guide. Chicago: SPSS Inc; 2008.
- Weiber R, Mühlhaus D. Strukturgleichungsmodellierung Structural Equation Modeling. Berlin: Springer; 2009.
- Raykov T, Marcoulides GA. A first course in structural equation modeling. Mahwah: Lawrence Erlbaum Associates; 2006.
- George D, Mallery P. SPSS for Windows Step by Step: A Simple Guide and Reference, 18.0 Update. Boston: Allyn & Bacon; 2010.
- Huber PJ, Ronchetti EM. Robust Statistics. Hoboken, NJ: John Wiley & Sons; 2009.
- Grissom RJ, Kim JJ. Effect sizes for research. Univariate and multivariate applications. New York: Routledge; 2012.
- Enders CK. Applied missing data analysis. New York: Guilford; 2010.
- Donders AR, van der Heijden GJ, Stijnen T, Moons KG. Review: a gentle introduction to imputation of missing values. J Clin Epidemiol 2006 Oct;59(10):1087-1091. [CrossRef] [Medline]
- Sterne JA, White IR, Carlin JB, Spratt M, Royston P, Kenward MG, et al. Multiple imputation for missing data in epidemiological and clinical research: potential and pitfalls. BMJ 2009;338:b2393 [FREE Full text] [Medline]
- O'Neil KM, Penrod SD, Bornstein BH. Web-based research: methodological variables' effects on dropout and sample characteristics. Behav Res Methods Instrum Comput 2003 May;35(2):217-226. [Medline]
- Kongsved SM, Basnov M, Holm-Christensen K, Hjollund NH. Response rate and completeness of questionnaires: a randomized study of Internet versus paper-and-pencil versions. J Med Internet Res 2007;9(3):e25 [FREE Full text] [CrossRef] [Medline]
- Leece P, Bhandari M, Sprague S, Swiontkowski MF, Schemitsch EH, Tornetta P, et al. Internet versus mailed questionnaires: a controlled comparison (2). J Med Internet Res 2004 Oct 29;6(4):e39 [FREE Full text] [CrossRef] [Medline]
- van den Berg MH, Overbeek A, van der Pal HJ, Versluys AB, Bresters D, van Leeuwen FE, et al. Using web-based and paper-based questionnaires for collecting data on fertility issues among female childhood cancer survivors: differences in response characteristics. J Med Internet Res 2011;13(3):e76 [FREE Full text] [CrossRef] [Medline]
- Rhodes SD, Bowie DA, Hergenrather KC. Collecting behavioural data using the world wide web: considerations for researchers. J Epidemiol Community Health 2003 Jan;57(1):68-73 [FREE Full text] [Medline]
- Joinson A. Social desirability, anonymity, and Internet-based questionnaires. Behav Res Methods Instrum Comput 1999 Aug;31(3):433-438. [Medline]
- Houston TK, Cooper LA, Vu HT, Kahn J, Toser J, Ford DE. Screening the public for depression through the Internet. Psychiatr Serv 2001 Mar;52(3):362-367. [Medline]
- Klovning A, Sandvik H, Hunskaar S. Web-based survey attracted age-biased sample with more severe illness than paper-based survey. J Clin Epidemiol 2009 Oct;62(10):1068-1074. [CrossRef] [Medline]
|ADHD: Attention-Deficit/Hyperactivity Disorder|
|ADHS-SB: ADHD Self Rating Scale|
|AGFI: Adjusted Global Fit Index|
|CAARS: Conners Adult ADHD Rating Scales|
|CAARS-S: CAARS self-report|
|DSM-IV: Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition|
|GFI: Global Fit Index|
|ICD-10: International Classification of Diseases—Tenth Edition|
|MCAR: Missing completely at random|
|PS: Probability of Superiority|
|RMR: Root Mean Square Residual|
|SRMR: Standardized Root Mean Square Residual|
|WURS-k: Wender Utah Rating Scale-Short Form|
Edited by G Eysenbach; submitted 17.06.12; peer-reviewed by L Whitehead, T Donker; comments to author 26.09.12; revised version received 15.10.12; accepted 17.01.13; published 21.03.13Copyright
©Oliver Hirsch, Franziska Hauschild, Martin H. Schmidt, Erika Baum, Hanna Christiansen. Originally published in the Journal of Medical Internet Research (http://www.jmir.org), 21.03.2013.
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