GraphPad Statistics Guide

Interpreting results: Number at risk

Interpreting results: Number at risk

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Interpreting results: Number at risk

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Number of subjects at risk at various times

Since the number at risk applies to a range of days, and not to a single day, the table is a bit ambiguous. The values tabulated are the number of subjects at risk at the start of that day (which can be different than those at risk at the end of that day).

Here are values of that table for the control group of the sample data (comparing two groups) that you can choose from Prism's Welcome dialog.

Days

Standard

0

8

46

8

64

6

78

5

124

4

130

3

150

2

The experiment starts with 8 subjects receiving standard therapy. There are still 8 subjects at risk at the beginning of day 46, and this is shown on the table. During day 46, one of the patients receiving standard therapy died and the data for another was censored. So 6 patients remain at risk between day 46 and the beginning of day 64, and this tabulated. On day 64, data on another patient is censored, so 5 patients are at risk until the beginning of day 78. The next death occurs on day 78, so 4 subjects are at risk until the beginning of day 124....

Prism does not graph this table automatically. If you want to create a graph of number of subjects at risk over time, follow these steps:

1.Go to the results tab for number of subjects at risk.

2.Click New, and then Graph of existing data.

3.Choose the XY tab and a graph with no error bars.

4.Change the Y-axis title to “Number of subjects at risk” and the X-axis title to “Days”.