Relative Risks table for Fit Cox Model with Fixed Predictors only

Find definitions and interpretation guidance for every statistic in the Relative Risks tables.

In This Topic

Relative risks
Confidence interval for relative risks (95% CI)

Relative risks

The relative risk compares the risks of two groups.

Interpretation

Use the relative risk to assess the risk between different values of the predictor variables. Minitab displays a separate table of relative risks for categorical and continuous variables.

Categorical predictor

In the Relative Risks for Categorical Predictors table, Minitab sets up the comparison by listing the levels in 2 columns, Level A and Level B. The relative risk describes the change in how likely the event is to occur for level A relative to level B. Relative risks that are greater than 1 indicate that the event is more likely at level A. Relative risks that are less than 1 indicate that the event is less likely at level A. For example, in the following results the risk of experiencing the event for patients in stage IV is 5.5 times higher than the risk for patients in Stage I.

Continuous predictor

In the Relative Risks for Continuous Predictors table, Minitab displays the unit of change and the relative risk. The relative risk describes the change in how likely the event is to occur for one unit of change. Relative risks that are greater than 1 indicate that the event is more likely to occur as the predictor increases. Relative risks that are less than 1 indicate that the event is less likely to occur as the predictor increases. For example, in the following results a patient is 1.02 times more likely to experience the event for each increase of 1 year to their age.

Relative Risks for Continuous Predictors

	Unit of Change	Relative Risk	95% CI
Age	1	1.0192	(0.9911, 1.0481)

Relative Risks for Categorical Predictors

Level A	Level B	Relative Risk	95% CI
Stage
II	I	1.1503	(0.4647, 2.8477)
III	I	1.9010	(0.9459, 3.8204)
IV	I	5.5068	(2.4086, 12.5901)
III	II	1.6526	(0.6819, 4.0049)
IV	II	4.7872	(1.7825, 12.8566)
IV	III	2.8968	(1.2952, 6.4788)

Confidence interval for relative risks (95% CI)

These confidence intervals (CI) are ranges of values that are likely to contain the true values of the relative risks.

Because samples are random, two samples from a population are unlikely to yield identical confidence intervals. However, if you take many random samples, a certain percentage of the resulting confidence intervals contain the unknown population parameter. The percentage of these confidence intervals that contain the parameter is the confidence level of the interval.

The confidence interval is composed of the following two parts:

Point estimate: The point estimate is the estimate of the parameter that is calculated from the sample data.
Margin of error: The margin of error defines the width of the confidence interval and is affected by the range of the event probabilities, the sample size, and the confidence level.

Interpretation

Use the confidence interval to assess the estimate of the relative risks. For example, with a 95% confidence level, you can be 95% confident that the confidence interval contains the value of the relative risk for the population. A confidence interval that contains 1 indicates that you cannot determine that the variable has an effect for the specified level of confidence. If a confidence interval does not contain 1, the confidence interval helps you assess the practical significance of your results. Use your specialized knowledge to determine whether the confidence interval includes values that have practical significance for your situation. If the interval is too wide to be useful, consider increasing your sample size.