This menu allows you to calculate the number of replicates (sample size) or the power required
for a McNemar test. The McNemar test is useful for analyzing studies where subjects are assessed
before and after a treatment. The response on each occasion is assumed to be categorized by a
factor with two levels, with level 1 usually representing a negative response, and level 2 a
positive response. The test is based on a table giving the numbers of subjects giving each
combination of responses over the two occasions.
Calculation
Specifies the calculation to be carried out: Sample size, or Power.
Probability of change
Specifies the overall probability of change, e.g. changes from positive to negative, or
negative to positive.
Ratio of probabilities
Specifies the ratio of the probabilities of the two types of change, e.g. ratio between
changes from positive to negative versus negative to positive.
Significance level Alpha
Specifies the significance level at which the response is to be tested.
Probability of detection (Power)
For a sample size calculation this specifies the required probability for detection of the
response (that is, the power of the test).
Sample Size
For a power calculation this specifies the sample size to be used to calculate the probability
of detection (power).
Type of Test
Allows you to choose either a one-sided or two-sided test.
Method
Specifies the method for the test that is to be done. The normal approximation setting
relates to a test based on the Normal approximation, while the exact assumes an exact
test using the binomial distribution.
Power Plot
When selected, produces a plot of power versus sample size. When Sample Size is selected
for the type of calculation the plot is generated using 11 replication values
centred around the required number of replicates for the requested power. When Power
is selected you can specify a range of sample size values for the plot in the
spaces provided.