For the treatment of postmenopausal symptoms, a novel estrogen receptor agonist is being studied. A prospective research found that the medicine raises the incidence of DVT in treated women who smoke compared to untreated women who smoke, with a relative risk (RR) of 1.70 and a p-value of 0.01. In nonsmokers, there is no increased incidence of DVT with drug use (RR = 0.96; p-value = 0.68). Which of the following best characterizes this occurrence?

Question

Quizplus · Accepted Answer

Eductional Objective: When the influence of an exposure on an outcome is modified by another variable, this is referred to as effect modification. It can be discovered via stratified analysis (diverging the cohort into distinct subgroups), as the measures of association will differ between strata. In this scenario, smoking status altered the effect of the novel estrogen receptor agonist (exposure) on the occurrence of deep vein thrombosis (DVT) (outcome). Using stratified analysis according to smoking status:
Effect modification is not a bias (Choices D and E), because it is not the result of faults in the study's design or analysis stages. It is a natural occurrence that should be described rather than rectified.
Effect modification is sometimes mistaken with confounding (Choice A), although stratified analysis can assist in distinguishing between these two instances. 
Different strata will have different measures of association with effect modification, as illustrated in this example of the connection between taking the estrogen receptor and the risk of DVT among smokers vs nonsmokers. Stratification, on the other hand, frequently displays no substantial difference between strata when confounding is present. In an investigation of primary school pupils (of all grade levels), for example, age can be a confounder that muddies the relationship between shoe size and IQ. On first glance, children with larger shoe sizes may appear to be more clever. This link, however, is most likely related to age rather than shoe size, because older children have both larger feet and higher IQ.  When older and younger children are analyzed separately (stratification based on the confounder), the association between shoe size and intelligence disappears.

For the Treatment of Postmenopausal Symptoms, a Novel Estrogen Receptor