EXAMPLE 7.17
Degrees of freedom for directed reading assessment. For the DRP study of Example 7.11, the following table summarizes the data:
| Group | n | s | |
|---|---|---|---|
| 1 | 21 | 51.48 | 11.01 |
| 2 | 23 | 41.52 | 17.15 |
For greatest accuracy, we will use critical points from the t distribution with degrees of freedom given by the preceding equation:
This is the value that we reported in Example 7.14 (pages 441–442), where we gave the results produced by software.