Rademakers et al. BMC Public Health 2012, 12:577 http://www.biomedcentral.com/1471-2458/12/577 Table 2 Data quality and item-rest correlations of the Dutch 13-item PAM (N = 1837) Item N Mean SD Median % missing PAM values score % not Item-rest applicable correlation 1 2 3 4 5 6 7 8 9 1788 3.32 0.71 1542 3.20 0.69 1716 3.10 0.73 1736 3.20 0.66 1815 3.24 0.60 1805 3.29 0.61 1487 3.30 0.57 1771 3.23 0.67 1733 3.10 0.67 10 1565 3.04 0.66 11 1694 2.96 0.70 12 1667 2.62 0.75 13 1678 2.84 0.70 3 3 3 3 3 3 3 3 3 3 3 3 3 1.0 3.3 1.5 0.4 0.5 0.9 1.6 0.9 1.4 1.7 1.0 1.1 1.0 1.7 12.8 5.1 5.1 0.7 0.9 17.5 2.7 4.3 13.1 6.8 8.1 7.6 0.49 0.50 0.60 0.54 0.62 0.55 0.62 0.66 0.64 0.51 0.61 0.50 0.46 The item response is high, few missing values are reported (between 0.4% and 3.3%). Three items (7, 10 and 2) are scored as ‘not applicable’ by more than 10% of the participants. For item 7 (‘I am confident that I can follow through on medical treatments I need to do at home’) and item 10 (‘I have been able to maintain the lifestyle changes for my health that I have made’) this may actually be the correct answer. Item 2 (‘Taking an active role in my own health care is the most important factor in determining my health and ability to function’) requires rephrasing in the Dutch version: it has the high- est percentage (3.3%) of missing values and furthermore 12.8% scored the item as not applicable, which is in- appropriate since it is a general statement which applies to all participants. Internal consistency was measured as the Cronbach’s α and inter-item correlations. Cronbach’s α for the sum scale was 0.88, which is similar to the Danish version (0.89) and is considered as a good level of internal consistency. The inter-item correlations ranged from 0.14-0.63. Item-rest correlations per item to the sum scale were moderate (for item 1 and 13) to strong (for all other items) and varied between 0.46 and 0.66. 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. These data were compared to the Danish and American scores (Table 3). In the Dutch sample, there is a clear association between gender, age, educational level, self-reported health and patient activation score. In general male, younger, higher educated and healthier participants have higher scores on the PAM 13-Dutch. Self-reported health is the most distinguishing variable in this respect: whereas almost two thirds (64.6%) of the Page 5 of 7 persons who report poor health have activation level 1 or 2, most people who report to be in good or very good health have activation level 3 or 4. Comparing the Dutch results to the Danish and Ameri- can data, we see that the Dutch mean PAM score (61.3) is comparable to the American (61.9) but somewhat lower than the Danish (64.2). While in the other countries women score higher on the PAM-13 than men, in the Netherlands the opposite is true. Associations with age, educational level and self-reported health in the three countries are similar. Also in Denmark and the USA, the association with self-reported health is strongest. Validation To validate the PAM 13-Dutch, the test-retest reliability was established (Table 4). On item level, the correlations between the first and the second measurement varied between 0.25 and 0.49 (p < .001), and was moderate on average. For the scale as a whole, the correlation was 0.47 (p < .001). To establish construct validity, correlations between the PAM scores and the SBSQ-D as a measure of Health literacy were computed. In our sample 23 respondents scored low on Health literacy (score of 2 or less on the SBSQ-D [15]), their mean PAM score was 48.6. Most participants (N = 1814) scored adequate on the SBSQ-D (score higher than 2). Their mean PAM score was much higher (61.4) compared to the low literacy group, indi- cating that as health literacy increases the activation level of patients generally goes up. The overall correl- ation between the SBSQ-D and PAM scores however was weak to moderate (r = 0.28). Discussion The PAM-13 Dutch is a reliable instrument to measure patient activation. The level of internal consistency is good (α = 0.88) and item-rest correlations are moderate to strong. Compared to the Danish data, the internal consistency as measured by Cronbach’s α is comparable in the Dutch sample. Unfortunately, there is no α pub- lished for the American sample. Internal consistency might further be improved by rephrasing item 2 (‘Taking an active role in my own health care is the most import- ant factor in determining my health and ability to func- tion’) which has the highest percentage of missing values, a high and inappropriate level of ‘non applicable’ scores and a relatively low item-rest correlation. Though the individual item sequence in our study did not exactly follow the original US scale, in general the progressing difficulty of the items is reflected in the mean scores. Further validation in other Dutch samples and more specific statistical (Rasch) analyses will have to confirm whether the sequence of the original US scale will re- quire readjustment in the Netherlands.