TOPIC 14: DETERMINING CAUSAL
AND RISK FACTORS FOR
In this lecture, we will begin to study the ways in which we assess causal factors
and risk factors for common chronic diseases such as cancer and cardiovascular
disease. We’ve already seen that we cannot determine the risk factors by
identifying the nature of the causal agent (such as is the case with a
pathoetiological diagnosis). Therefore, unlike in the case of infectious diseases,
we will need to establish new methods for determining the causal pathway from
the healthy state to the diseased state and, therefore, for identifying the risk
factors that increase one’s risk for the disease.
1. This link is to a website devoted to scientific research and design. Although there are
some deviations from standard definitions in their discussions, it is still an
informative source for basic information regarding various types of research designs.
— when we wish to establish the causal and risk factors determining variability in
incidence rates of non-communicable diseases such as cancer and heart disease,
we are asking “which exposures increase disease risk?”
— often, epidemiological evidence suggests the nature of the exposure
— in this case, we then even more advanced questions such as:
— what duration of the exposure is critical for risk of disease?
— what is the optimal timing of the exposure for risk of disease?
— what is the interval between exposure and the beginning of the symptomatic
phase of the natural history of the disease?
— to answer these questions, we use research designs:
i) Experimental Designs
1) Randomized Control Trial
— randomly assign subjects to groups
— expose 1 group to a treatment/intervention, risk factor, etc.
— measure outcome after a specific interval 211212
a Control Group
— “gold standard” for proof
— first, we must decide which exposures to apply
— we also must decide what duration and timing of the exposure to use, and
what interval between the exposure and outcome measurement to use
— also, sometimes we cannot satisfy ethical considerations using an RCT
2) Pre-Post Study
— everyone in the study gets exposed to a particular factor
— assessments are made both before and after the exposure
— these designs often do not show causality
— maturation of subjects, and regression to the mean are just two
examples of ways in which the results of these studies can be spurious
ii) Quasi-experimental Designs
1) Case-Control Study (observational study)
— compare the group with a particular outcome (i.e., a particular disease)
versus a group w