Table 4.
Sample Size Requirements for a Unilateral Study Design
| Mean Difference | SD=5 | SD=4 | SD=3 | SD=2 |
|---|---|---|---|---|
| 1 point | 394 | 250 | 143 | 64 |
| 2 points | 100 | 64 | 37 | 17 |
| 3 points | 45 | 29 | 17 | 9 |
| 4 points | 26 | 17 | 10 | 6 |
| 5 points | 17 | 12 | 7 | 4 |
| 6 points | 12 | 9 | 6 | 4 |
| 7 points | 10 | 7 | 5 | 3 |
| 8 points | 8 | 6 | 4 | 3 |
| 9 points | 6 | 5 | 4 | 3 |
| 10 points | 6 | 4 | 3 | 3 |
Required sample sizes when planning a study to assess differences in the total histological score values with one joint operated per animal (unilateral study design) are based on 80% statistical power using the two-sample Student t-test and display the numbers of joints needed to treat to detect the respective mean difference in the total histological score value according to Sellers et al.10 Mean differences are also applicable to any other scoring system, animal and defect model when one joint is operated per animal or treatment versus sham groups with one joint per animal. SD, standard deviation.