I am planning to use the WHODAS 2.0 to look at functioning in individuals with mental health difficulties. I am trying to decide on the sample size that I need to recruit in order to have sufficient statistical power. The manual does not include a standard deviation score from what I can see. Does anyone know how to go about calculating an appropriate sample size?
The sample size should be determined by the research design and thus the actual statistical analysis method dictated by the research design. As I recall the WHODAS 2.0 is a 36 item instrument. If any multivariate analysis is required by the actual research design, then the sample size may need to be larger compared to using a univariate approach. Once the design and the analysis method is chosen, then the sample size can be calculated according to the power level that you desire.
Thanks for your response. I don't fully understand the different types of analysis that you mention, but my intention would be to try to see if there are corrolations between variables e.g. are there corrolations between levels of anxiety and poor functioning? I am planning on using the WHODAS with two different groups of peoples and running comparisons.
Generic assessment instrument for health and disability
Used across all diseases, including mental, neurological and addictive disorders
Short, simple and easy to administer (5 to 20 minutes)
Applicable in both clinical and general population settings
Produces standardized disability levels and profiles
Applicable across cultures, in all adult populations
Direct conceptual link to the International Classification of Functioning, Disability and Health (ICF)
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