In a selected study of bronchogenic cancer, it was found that in people smoking 1 pack per day (PPD) of cigarettes, the relative risk (RR) was 2.4. For those smoking 2 PPD, the RR was 3.0. For those smoking 3 PPD, the RR was 4.1. The corresponding p-values for these RRs were all

Question

In a selected study of bronchogenic cancer, it was found that in people smoking 1 pack per day (PPD) of cigarettes, the relative risk (RR) was 2.4.  For those smoking 2 PPD, the RR was 3.0.  For those smoking 3 PPD, the RR was 4.1.  The corresponding p-values for these RRs were all <0.05 with no overlap in the corresponding confidence intervals.  Which of the following statements is true regarding these findings?

Quizplus · Accepted Answer

Relative risk (RR) is used as a measure of association in cohort studies. It is the ratio of the risk in the exposed group to that in the unexposed group. A RR >1 means that there is a positive association between the risk factor and the outcome. A RR <1 means that there is a negative association between the risk factor and the outcome. The farther the value of RR from 1, the stronger the association. In the example, the RR for bronchogenic cancer in smokers is >2, thereby indicating a strong association between smoking (risk factor/exposure) and bronchogenic cancer (outcome). When exposure is measured on a continuous scale (eg, number of packs per day [PPD]), the classification in 2 or more ordinal categories enables the risk to be assessed as a function of exposure, and the dose-response effect can be calculated for the exposure and outcome. This example illustrates a dose-response relationship between smoking and bronchogenic cancer (ie, the RR for bronchogenic cancer increases as the number of smoked PPD increases). (Choices A, B, C, and E) In the study, there was a strong association between cigarette smoking and bronchogenic cancer. There was also a clear dose-response relationship between smoked PPD and bronchogenic cancer. Educational objective: Know how to interpret the strength of association and dose-response relationship from a study.

In a Selected Study of Bronchogenic Cancer, It Was Found