ABSTRACT
We can use the same SAS programme to determine the required sample size to achieve 80 per cent power, other parameters remaining the same. The number of subjects required in each group is 41 (see Figure 5.6)
Comparison of Tow Means (unpaired data) Finding number of subjects (n) per group
Example 5.5: Estimating Sample Size for Difference in Means (Related Groups)
In a paper by Hart, Wearing, and Conn (1995) which reported on the evaluation studies that were conducted as part of a programme on a Whole School Approach to
Discipline and Student Welfare (WSADSW-Statewide Australian Programme), changes in teachers’ stress, discipline skills and aspects of school organizational climate were analyzed. Data abstracted from the paper include:
Before WSADSW After WSADSW p-values paired Variable n r* M† SD M SD t-test
A five-point rating scale, the General Strain Index, was used to assess teachers’ psychological distress. Student Misbehaviour was measured using a single self-report scale. Teachers’ rated on a 100-point scale their perceptions, related to one class, of the amount of time they spent dealing with student misbehaviour in that class.
