Statistics Question
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Echocardiogram data was collected to assess the association of the Wall Motion Score Index (WMSI) and mortality. Time was defined as the number of months survived after a heart attack. The WMSI is a measure of how the segments of the left ventricle of the heart are moving relative to the number of segments. The data consists of 124 patients, 85 of whom died. Age was measured in years when the heart attack occurred. The table below contains the parameter estimates from hazard regression models.
| Model | |||||
|---|---|---|---|---|---|
| Variable | Null | 1 | 2 | 3 | 4 |
| WMSI | 0.12 | 0.01 | 0.15 | 0.14 | |
| Age | 0.01 | 0.01 | |||
| WMSI × Time | -0.87 | -0.88 | |||
| -2lnL | 603.6 | 597.9 | 589.3 | 585.2 | 592.6 |
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- Test the unadjusted association of WMSI and survival. Compute the unadjusted hazard ratio for WMSI. Comment on the association in terms of direction, magnitude and significance.
- Assess the proportionality assumption.
- Using the appropriate model, test to see if Age should be included in the model. Compute the hazard ratio for Age using a 5-year interval. Interpret the hazard ratio.
- Interpret the association of the WMSI and mortality. Use your final model to calculate the hazard ratio(s) for WMSI. If your final model contains a time interaction, use the following ln(time) values; -1.04, 0.104 and 0.443. (These values were calculated by subtracting the ln of the mean time from the ln of 7.5, 23.5 and 33.0. These are the 25th, 50th and 75th percentiles of time.)
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