Rademakers et al. BMC Public Health 2012, 12:577 http://www.biomedcentral.com/1471-2458/12/577 take action; items 3-8), level 3 (taking action; items 9-11) and level 4 (staying on course under stress; items 12 and 13) [2]. To establish the level of Health Literacy, we used the Dutch translation of the Set of Brief Screening Questions (SBSQ-D) and followed the corresponding scoring instructions [15]. This is a self report instrument which consists of three items and focuses on the ability to read and understand medical information. The Dutch version of the Set of Brief Screening Questions (SBSQ-D) of functional health literacy included: 1) “How often do you have someone help you read materials?”, 2) “How confident are you filling out medical forms by yourself?” and 3) “How often do you have problems learning about your medical condition because of difficulty understand- ing written information?” Question 1) and 3) had re- sponse options never, occasionally, sometimes, often or always, whereas for question 2) they were extremely, quite a bit, somewhat, a little bit and not at all. Answers were scored on a Likert scale from 1 to 4 where 1 was assigned to never or extremely, and 4 to merged responses often/always and a little bit/not at all. Cron- bach’s α for the SBSQ-D was 0.73, indicating acceptable internal consistency. Statistical analyses The analyses were performed on the data of study A, ex- cept for the test-retest reliability where the datasets from study A and B were combined. For comparability with the Dutch and American studies, we focused in our ana- lyses on the subsample in study A of people with a chronic illness. To establish the psychometric properties of the PAM 13-Dutch the data quality and internal consistency of the instrument were assessed. For data quality, we looked at the mean (with standard deviation), median, percentage of missing data, and percentage of ‘non ap- plicable’ answers. Internal consistency was measured as the Cronbach’s α, inter-item and item-rest correlations (Pearson’s r). Item-rest correlations are the correlations between an item and the scale that is formed by all other items. Since very strong correlations are rare in the so- cial sciences, in our study a correlation ≥ 0.50 is consid- ered strong, r ≥ 0.30 moderate and r ≥ 0.10 weak [17]. Furthermore, the distribution of levels of activation and adjusted mean overall scores in the Dutch sample were described (by gender, age, educational level and self- reported health) and the latter were compared to the Danish and American scores. To validate the PAM 13-Dutch, the test-retest reliabil- ity as an indicator of stability and construct validity was established. We also looked at associations between the PAM scores and a measure of Health Literacy to Page 4 of 7 establish the construct validity. Analyses were performed with STATA 10. Results Participants Study A In study A 2542 questionnaires were sent of which 2070 were completed and returned. The gross response was therefore 2070/2542*100 = 81.4%. Of this sample, the data of 233 respondents were excluded: 198 because they had filled out less than 7 items on the PAM-Dutch questionnaire and 35 because they had responded to all the items with totally agree or disagree. These are requirements to be able to be able to compute a valid PAM-score. The net response rate in study A was there- fore 1837/2542*100 = 72.3%. The mean age of these par- ticipants was 58.7 years (SD 0.38) (age 15 - 93 years). Of the sample, 56.2% was female. Asthma, COPD and dia- betes were the most frequent reported chronic illnesses with a prevalence in the sample of respectively 20.3, 13.5 and 11.5 percent. Study B In study B 973 questionnaires were sent to patients with Asthma and/or COPD, who had also participated in study A. Of these questionnaires 705 were completed and returned (gross response: 705/973*100 = 72.5%). Of these, 33 respondents were excluded because they had filled out less than 7 items on the PAM-Dutch question- naire and 26 because they had responded to all the items with totally agree or disagree. The net response for study B was: 672/973*100 = 69.1%. The mean age of these par- ticipants was: 58.7 years (SD 0.58) and 55.4% was female. The time between data collection of study A en B was approximately 8 to 12 weeks. Of the remaining 672 respondents in study B, the data of 499 could be used for the test-retest analysis. The other 173 respondents had been excluded in study A be- cause they had not filled out the PAM according to the requirements. Psychometric properties To establish the psychometric properties of the PAM 13-Dutch the data quality, internal consistency and item-rest correlations were assessed (Table 2). With respect to data quality, we looked at the mean (with standard deviation), median, percentage of missing data, and percentage of ‘non applicable’ answers. Over- all, the mean scores on the items varied between 2.62 and 3.32. In general, the last items have a lower mean score compared to the earlier items in the questionnaire. However, in our results the individual item sequence did not exactly follow the original US scale (from higher to lower scoring items).