Determining Sample Size Adequacy Research Study Sample Size and Your HCIP Determining

Determining Sample Size Adequacy
Research Study Sample Size and Your HCIP
Determining Sample Size Adequacy when Appraising a Published Research Report: Power analysis is the best approach for determining sample size. Researchers should be reporting the necessary sample size in studies that test relationships/effects, as indicated by their conduct of a power analysis. When they do, the report will include something like, “an 80% power was achieved” or “a power analysis indicated that 214 subjects are needed to….” 
Addressing Sample Size Adequacy in your HCIP Evidence Tables:
If a study sample included at least as many subjects as were indicated necessary through the researchers’ power analysis, then, you should state, “Sample size adequate, as indicated by power analysis” as a strength in the appraisal column of your evidence table.
If not reported, state “No power analysis reported” as a limitation in the appraisal column of your evidence table.
Appraising Sample Adequacy when No Power Analysis was Reported:
In the case of no power analysis, for the HCIP, you can use the following Rule of Thumb to determine the sample size needed in a given study that tests relationships/effects and then compare it to the actual sample size:
N > 50 + 8m
N = sample size
m = number of independent variables/predictors tested in the study (all, not just YOUR selected interventions)
For example, in a study where the effects of three predictor variables (e.g., participant age, experimental intervention, placebo) on a given outcome are tested, at a minimum, 74 participants are needed:
50 + (8 x 3) = 74 to ensure sample adequacy.
When appraising a study testing relationships as in the above example:
If the final sample included 74 or more subjects, document “Per rule of thumb, sample size was adequate” as a strength in the appraisal column of your HCIP evidence table.
If the final sample included less than 74 subjects, document “Per rule of thumb, sample adequacy was not achieved” as a limitation in the appraisal column of your HCIP evidence table.
As a reminder, the following points regarding study sample should be addressed as a strength or limitation in the appraisal column of all your HCIP evidence tables:
Sampling strategy used
Sample size adequacy
Homogeneity/Heterogeneity- As yourself, was the study sample representative of the general/target population? Think about participant characteristics?
Participant recruitment strategy- Was there anything about the recruitment procedure(s) that may have decreased or increased the risk of introducing bias in the study results?