A group of investigators is exploring trends in the incidence of coronary heart disease (CHD) in a large population. The investigators studied several factors in relation to the incidence of the disease. The relationships between cigarette sales in the population (in average number of cigarette packs sold per person per day) and the incidence of CHD (per 1000 people) over time are given on the figure below: Which of the following is the best statement concerning the results of the study?
A)Coronary heart disease (CH
D) incidence shows no stable trend over time
B)Individuals from this population who quit smoking have a decreased risk of CHD
C)Sales of cigarettes in the population increased over time
D)The plot cannot provide individual-level conclusions
E)There are discordant changes in cigarette sales and CHD incidence

Question

A group of investigators is exploring trends in the incidence of coronary heart disease (CHD) in a large population.  The investigators studied several factors in relation to the incidence of the disease.  The relationships between cigarette sales in the population (in average number of cigarette packs sold per person per day) and the incidence of CHD (per 1000 people) over time are given on the figure below:  Which of the following is the best statement concerning the results of the study?
A)Coronary heart disease (CH
D) incidence shows no stable trend over time 
B)Individuals from this population who quit smoking have a decreased risk of CHD 
C)Sales of cigarettes in the population increased over time 
D)The plot cannot provide individual-level conclusions 
E)There are discordant changes in cigarette sales and CHD incidence

Quizplus · Accepted Answer

Explanation: As the graph has 3 axes and only 1 curve, each point plotted on the curve provides information about 3 variables: cigarette sales (in average number of cigarette packs sold per day per person), incidence of coronary heart disease (CHD) (per 1000 people), and time (year). For example, the top right of the graph shows that, in ~1970, an average of ~1.5 cigarette packs was sold per day per person, and the incidence of CHD was ~90 per 1000 people. Similarly, the lower left of the graph shows that, in ~1990, an average of ~0.5 cigarette packs were sold per day per person, and the incidence of CHD was ~50 per 1000 people. However, no individual-level conclusions can be ascertained from the data. The study described is a typical ecologic (correlational) study based on population-level information rather than individual-level information. Applying population-level information to an individual level may lead to a bias called ecologic fallacy. (Choices A, C, and E)The plot illustrates the temporal trends of cigarette sales and incidence of CHD, both of which appear to have steadily declined over time in the population. Because both variables declined progressively, the changes over time are described as concordant, not discordant. (Choice B)It cannot be concluded directly from this plot that quitting smoking decreases the risk of CHD for a person living in this population as correlation does not imply causation. For instance, plotting personal computer usage rather than cigarette sales in this population would likely show an increasing (rather than a decreasing) trend over time; however, this would not mean that personal computer use decreases the risk of CHD. Educational objective: Ecologic studies give population-level information, not individual-level information.

A Group of Investigators Is Exploring Trends in the Incidence