Measure a continuous outcome y in each subject at the start and end of the study period. For each subject, calculate the change Δ = ystart - yend. Compare the mean value of Δ to 0. This requires the standard deviation S(Δ). The estimate of S(Δ) should be based on data from other subjects who were followed for similar time periods.

Instructions: Enter parameters in the red cells. Answers will appear in blue below.

α (two-tailed) = Threshold probability for rejecting the null hypothesis. Type I error rate.
β = Probability of failing to reject the null hypothesis under the alternative hypothesis. Type II error rate.
E = Effect size
S(Δ) = Standard Deviation of the CHANGE in the outcome. (If you don't know S(Δ), click here to calculate it.)

The standard normal deviate for α = Zα =

The standard normal deviate for β = Zβ =

A =

B = (Zα+Zβ)2 =

C = (E/S(Δ))2 =

AB/C = 0.00

Group size N:

Reference: Rosner B. Fundamentals of Biostatistics. 4th ed. Duxbury Press; 1995. Page 221.