Analysis choices for survival analysis

From the results, you can click the analysis parameters button to bring up the parameters dialog, but there is little reason to ever do this as the default input choices are totally standard and the output choices can also be made on the graph.

Input

The default choices are to use the code '1' for deaths and '0' for censored subjects, and these are almost universal. But you can choose different codes by entering values here. The codes must be integers.

Output

The choices on how to tabulate the results (percents or fractions, death or survival), can also be made on the Format Graph dialog.

If you choose to plot 95% confidence intervals, Prism 5 gives you two choices. The default is a transformation method, which plots asymmetrical confidence intervals. The alternative is to choose symmetrical Greenwood intervals. The asymmetrical intervals are more valid, and we recommend choosing them.

The only reason to choose symmetrical intervals is to be consistent with results computed by prior versions of Prism. Note that the 'symmetrical' intervals won't always plot symmetrically. The intervals are computed by adding and subtracting a calculated value from the percent survival. At this point the intervals are always symmetrical, but may go below 0 or above 100. In these cases, Prism trims the intervals so the interval cannot go below 0 or above 100, resulting in an interval that appears asymmetrical.