The Kaplan-Meier curve was designed in 1958 by Edward Kaplan and Paul Meier to deal with incomplete observations and differing survival times. Used in medicine and other fields, the K-M curve analyzes the probability of a subject surviving an important event. The event can be anything that marks a significant point in time or accomplishment. Subjects in K-M analysis have two variables: study period (from the beginning point to an end point) and status at the end of the study period (the event occurred, or the event didn't occur or is uncertain).
Set Up the Excel Spreadsheet
Name column A as "Study Period," column B as "Number at Risk," column C as "Number Censored," column D as "Number Died," column E as "Number of Survivors" and column F as "K-M Survival."
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Fill in the column values. Type in the study's periods in the Study Period column. In the Number Censored column, type how many people were excluded from the study at this point. A person can be censored because he dropped out of the study, his data is incomplete or the study ended before the event happened for him. In the Number Died column, type in the number of people who died in this period of the study.
Fill in the Number at Risk and Number of Survivors columns. For the first row, starting at cell B2, the number at risk is the total number of participants in the study. The number of survivors is the number at risk minus the number who died, or =B2-D2. The second and subsequent rows are calculated differently. The Number at Risk column is the number of survivors from the previous period minus how many people were censored, or =E3-C3. The number of survivors for this period is still the number at risk minus the number who died, or =B3-D3. Click cell B3 and drag to autofill the rest of the Number at Risk column. Click cell E3 and drag to autofill the rest of the Number of Survivors column.
Fill in the K-M Survival column to calculate the survival probability for each period of the study. For the first study period, the survival probability is the number of survivors divided by the number at risk, or =E2/B2. For the second and subsequent study periods, the survival probability is the previous period's survival probability multiplied by the number of survivors divided by the number at risk, or =F2*(E3/B3). Click cell F3 and drag to fill in the rest of the K-M Survival column.
Create the Kaplan-Meier Survival Plot
Select the values in the K-M Survival column, from cell F2 to the end of your data.
Click the "Insert" tab. In the Charts section, click the arrow next to the Insert Line Chart icon. Click the "Line with Markers" option. A chart appears on the worksheet.
Click "Select Data" on the Design tab to change the X-axis to reflect the correct study periods. The Select Data Source box opens. In the Horizontal (Category) Axis Labels section, click the "Edit" button. Click cell A2 and drag to the end of the data. Click "OK," and then click "OK" again. You now have a Kaplan-Meier survival plot.