Contents
How do you calculate sample size from effect size?
Generally, effect size is calculated by taking the difference between the two groups (e.g., the mean of treatment group minus the mean of the control group) and dividing it by the standard deviation of one of the groups.
What is Alpha in sample size calculation?
Components of sample size calculations
| Component . | Definition . |
|---|---|
| Alpha (type I error) | The probability of falsely rejecting H0 and detecting a statistically significant difference when the groups in reality are not different, i.e. the chance of a false-positive result. |
How to calculate Sample Size for ROC test?
If two ROC curves are passed to power.roc.test, the function will compute either the required sample size (if power is supplied), the significance level (if sig.level=NULL and power is supplied) or the power of a test of a difference between to AUCs according to the formula by Obuchowski and McClish, 1997 (formulas 2 and 3, p. 1530–1531).
How to calculate the power of a ROC curve?
If one or no ROC curves are passed to power.roc.test, a one ROC curve power calculation is performed. The function expects either power, sig.level or auc, or both ncontrols and ncases to be missing, so that the parameter is determined from the others with the formula by Obuchowski et al., 2004 (formulas 2 and 3, p. 1123).
How to calculate SIG level and power for ROC?
The null hypothesis is that the AUC of roc1 is the same than the AUC of roc2, with roc1 taken as the reference ROC curve. For the sample size, ncases is computed directly from formula 2 and ncontrols is deduced with kappa (defaults to the ratio of controls to cases in roc1 ). sig.level and power are solved as quadratic equations.
How is the sample size and power calculated?
For the sample size, ncases is computed directly from formula 2 and ncontrols is deduced from the ratio observed in roc1 and roc2 . sig.level and power are solved as quadratic equations. The variance and covariance of the ROC curve are computed with the var and cov functions.