Sample size calculation formula in "before-after" intervention studies with qualitative outcomes

Abstract

Dear Editor, In “before-after" intervention studies with qualitative outcome(s), we should not use the same formula when the outcome(s) are quantitative since the appropriate variance in this formula are not used and thus the sample size will not have adequate confidence and power. A formula for such studies is proposed to overcome problems highlighted above.

Keywords

• interventional design
• sample size