Hi all, hoping i can find some answers here for a bit of a problem i am having regarding a sample size calculation for a study I am soon to conduct.
The population size is 64 and fixed. 32 control and 32 intervention. No drop outs will occur in this trial. There will be a pre (baseline) test on all subjects (64) and post on each of the 2 groups of 32. The test will assess knowledge in the form of multiple choice questions. Each question will be assigned a mark of 1. I seek to show a statistically significant difference between both groups post intervention. My alpha is set to 0.05 and beta at 0.20. The two groups are identical in terms of selection of subjects (same age, gender, etc).
Ideally we wish to show that in the intervention group there is a greater change in mean scores when compared to control group. I wish to detect a difference of at least 5% between the two groups.
What i was wondering is:
- What is my required sample size for each group? As each group of participants is set at 32 and will not change, can i merely > the number of questions administered until reach an ideal number? I was estimating around 20 questions, 1 mark per question so 32X20X1 = 640 for each group.
Also how does 'effect size' come into play, i have heard this term but lack the statistical knowledge to understand it.
Much appreciated to anyone who can show me the working out for this
Damian
The population size is 64 and fixed. 32 control and 32 intervention. No drop outs will occur in this trial. There will be a pre (baseline) test on all subjects (64) and post on each of the 2 groups of 32. The test will assess knowledge in the form of multiple choice questions. Each question will be assigned a mark of 1. I seek to show a statistically significant difference between both groups post intervention. My alpha is set to 0.05 and beta at 0.20. The two groups are identical in terms of selection of subjects (same age, gender, etc).
Ideally we wish to show that in the intervention group there is a greater change in mean scores when compared to control group. I wish to detect a difference of at least 5% between the two groups.
What i was wondering is:
- What is my required sample size for each group? As each group of participants is set at 32 and will not change, can i merely > the number of questions administered until reach an ideal number? I was estimating around 20 questions, 1 mark per question so 32X20X1 = 640 for each group.
Also how does 'effect size' come into play, i have heard this term but lack the statistical knowledge to understand it.
Much appreciated to anyone who can show me the working out for this
Damian