The WEMWBS scales have been designed to be self-completed. Both digital and paper versions work well. If there is a need to help participants complete the scale by reading out items or filling in the questionnaire for them there is a risk that participants will respond more positively than if they were completing the questionnaire on their own. This could introduce bias into the study. As a rule of thumb studies need to include at least 30 people with data at two points in time or 30 people in each group to be compared. Some simple guidance on sample size calculation is available on page 38 of the user guide for researchers User guide for researchers.
The 14-item scale WEMWBS is very simple to score. The total score is obtained by summing the score for each of the 14 items. The scoring range for each item is from 1 – 5 and the total score is from 14-70. For more help with scoring WEMWBS please refer to the user guides available on the Resources Pages of the website which are available once your have registered to use the scale.
The 7-item scale SWEMWBS is more complicated to score and it is important that it is scored correctly in order for comparisons to be made across different studies. SWEWMBS is a shortened version of WEMWBS which is Rasch compatible. This means the seven items have superior scaling properties to the 14 items, but in order to take advantage of this and to compare results with those of other studies using the 7-item scale SWEMWBS, raw scores need to be transformed. Transformation just means that the total raw scores need to be converted as in this conversion table.
Both WEMWBS and the 7-item scale SWEMWBS scores approximate to a normal distribution, permitting parametric analysis. So the most statistically efficient approach to analysing data is to calculate means and standard deviations and compare results using Students T-test. A workbook for calculating change in scores and statistical significance is available in the Data Analysis section of the Resources Webpages which is available once your have registered to use the scale. The UK Population norms have been published and can be used as comparators for your scores (WEMWBS and SWEMWBS population norms Health Survey for England 2011).
Some investigators prefer to analyse their data using categorical approaches. Scores can be divided into high, average and low mental wellbeing using cut points. Several different cut-points have been used. One statistical approach is to put the cut points at plus or minus one standard deviation. This approach puts approximately 15% of the participants into high and 15% into low categories. In UK population samples, the top 15% of scores on WEWMBS range from 60-70 and the bottom 15% 14-42. For SWEMWBS comparable figures are 28-35 and 7-19.
If you have used a parametric approach to analysis (Students T-test), you need to compare your scores with population norms. Ideally, results should be adjusted for differences in age and sex distribution.
If you are using a categorical approach with WEMWBS, it is possible to find a point between low and average mental wellbeing which corresponds to the cut points on validated scales of mental illness such as the CES-D measure of depression (Donatella Bianca report). In the latter study, a score of 40 and below corresponded to probable depression and a score of 41- 44 to possible depression. NHS direct have used the cut point of 40 and below as the cut point for low mental wellbeing in their self-assessment scales. Similar cut points for SWEMWBS have been calculated in comparison with PHQ-9 and GAD-7 (Shah et al in press). Scores of 7-17 represent probable depression or anxiety; Scores of 18-20 suggest possible depression or anxiety.
As there is no gold standard for measuring high mental wellbeing all cut points are by definition arbitrary. A cut-point of 60 and above can be used to identify the top 15% of scores on WEMWBS and 28 and above for SWEMWBS.
How you analyse your information further will depend on your study design.
Individual-level differences: Neither of the measures was developed for monitoring change at the individual level or in clinical settings, but both the 14-item scale and 7-item scale WEMWBS have been shown to be responsive to change at the individual level and some practitioners are using the scales to help clients and patients think about ways in which their mental health is changing. Different statistical approaches give different results with regard to minimally important levels of change. For the 14-item scale WEMWBS the methods give a minimum of 3 points and a maximum of 8 points; for the 7-item scale SWEMWBS, a minimum of 1 point and a maximum of 3 points.