This menu allows you to calculate the number of replicates (sample size) or the power required
for assessing the correlation between two variables within a single group of subjects, or between
two groups of subjects. The correlation in this case is the product moment correlation coefficient,
as calculated by the CORRELATION function (and
so the variables are assumed to have Normal distributions). The calculations can be done for a
one-sample t-test (testing for evidence that the mean of the sample differs from a specific
value) or a two-sample test (testing that means of the samples are different).
Calculation
Specifies the calculation to be carried out: Sample size, or Power.
Test
Specifies the test to be carried out: One-sample, or Two-sample.
Correlation in Sample
For a one-sample test this specifies the correlation, and the assumption is to assess whether this is
non-zero. For a two-sample test this specifies the correlation within the first sample.
Correlation in Sample 2
For a two-sample test this specifies the correlation for the second sample.
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).
Replication Ratio (Sample 2:Sample 1)
It is generally assumed that the sizes of the samples in the two-sample test should be equal.
However, you can specify a ratio to indicate the size of the second sample in relation to
the size of the first sample
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.