Table 1.
Regression Equation between Point.Biserial Correlation (Cpbs) and Other Discrimination Indices
| Discrimination index | Equation of linear regression | r2 | SE | F‐statistic | Degree of freedom | SSreg | SSR |
|---|---|---|---|---|---|---|---|
| Ccit | y1=1.02×Cpbs | 1.00 | 0.00 | 3.74×10+30 | 23 | 0.74 | 0.00 |
| Cit | y3=1.04×Cpbs+0.10 | 0.99 | 0.02 | 351.20 | 23 | 0.87 | 0.06 |
| Cbs | y2=1.11×Cpbs+0.08 | 0.94 | 0.05 | 2,643.88 | 23 | 0.77 | 0.01 |
| D | y4=1.04×Cpbs+0.10 | 0.45 | 0.16 | 18.79 | 23 | 0.47 | 0.58 |
Ccit: Corrected item.total correlation, Cit: Item.total correlation, Cbs: Biserial correlation, D: Method of extreme group, SE: Standard error, SSreg: Sum of squared regressions, SSR: Sum of squared residuals.