Study design depends greatly on the nature of the research question. In other words, knowing what kind of information the study should collect is a first step in determining how the study will be carried out (also known as the methodology).
Let’s say we want to investigate the relationship between daily walking and cholesterol levels in the body. One of the first things we’d have to determine is the type of study that will tell us the most about that relationship. Do we want to compare cholesterol levels among different populations of walkers and non-walkers at the same point in time? Or, do we want to measure cholesterol levels in a single population of daily walkers over an extended period of time?
The first approach is typical of a cross-sectional study. The second requires a longitudinal study. To make our choice, we need to know more about the benefits and purpose of each study type.
Cross-sectional study
Both the cross-sectional and the longitudinal studies are observational studies. This means that researchers record information about their subjects without manipulating the study environment. In our study, we would simply measure the cholesterol levels of daily walkers and non-walkers along with any other characteristics that might be of interest to us. We would not influence non-walkers to take up that activity, or advise daily walkers to modify their behaviour. In short, we’d try not to interfere.
The defining feature of a cross-sectional study is that it can compare different population groups at a single point in time. Think of it in terms of taking a snapshot. Findings are drawn from whatever fits into the frame.
To return to our example, we might choose to measure cholesterol levels in daily walkers across two age groups, over 40 and under 40, and compare these to cholesterol levels among non-walkers in the same age groups. We might even create subgroups for gender. However, we would not consider past or future cholesterol levels, for these would fall outside the frame. We would look only at cholesterol levels at one point in time.
The benefit of a cross-sectional study design is that it allows researchers to compare many different variables at the same time. We could, for example, look at age, gender, income and educational level in relation to walking and cholesterol levels, with little or no additional cost.
However, cross-sectional studies may not provide definite information about cause-and-effect relationships. This is because such studies offer a snapshot of a single moment in time; they do not consider what happens before or after the snapshot is taken. Therefore, we can’t know for sure if our daily walkers had low cholesterol levels before taking up their exercise regimes, or if the behaviour of daily walking helped to reduce cholesterol levels that previously were high.
Longitudinal study
A longitudinal study, like a cross-sectional one, is observational. So, once again, researchers do not interfere with their subjects. However, in a longitudinal study, researchers conduct several observations of the same subjects over a period of time, sometimes lasting many years.
The benefit of a longitudinal study is that researchers are able to detect developments or changes in the characteristics of the target population at both the group and the individual level. The key here is that longitudinal studies extend beyond a single moment in time. As a result, they can establish sequences of events.
To return to our example, we might choose to look at the change in cholesterol levels among women over 40 who walk daily for a period of 20 years. The longitudinal study design would account for cholesterol levels at the onset of a walking regime and as the walking behaviour continued over time. Therefore, a longitudinal study is more likely to suggest cause-and-effect relationships than a cross-sectional study by virtue of its scope.
In general, the research should drive the design. But sometimes, the progression of the research helps determine which design is most appropriate. Cross-sectional studies can be done more quickly than longitudinal studies. That’s why researchers might start with a cross-sectional study to first establish whether there are links or associations between certain variables. Then they would set up a longitudinal study to study cause and effect.
Source: At Work, Issue 81, Summer 2015: Institute for Work & Health, Toronto
This column updates a previous column describing the same term, originally published in 2009.
36.When we are concerned with whether we are correct in inferring that a cause produced aneffect, we are concerned with the:
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37.Our ability to determine whether a change in the cause is statistically associated with a change inthe effect is referring to what type of validity?
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38.Identifying the population and sample precede which of the following tasks in a researchproject?
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39.Which of the following is not a characteristic of a cross-sectional study?
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40.Prospective studies are completed quickly since you only have to ask people to project what theywould do or how they will act in the future.
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41.Which of the following would serve as a “snap shot” of a phenomenon at one point in time?
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42.After a one-year study of the recidivism rates of boot camps in the state of Georgia, the lowestrates were found in the boot camps located in Macon. What units of analysis were used in thisstudy?
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43.Dr. Stone is interested in comparing the attitudes about teenage pregnancy between the UnitedStates and the Netherlands. He selects samples in both countries of 10 year old males andfemales and plans to survey a portion of them every other year for the next ten years. Stone isusing what technique?
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44.Which term best describes—an overly strict limitation on the kinds of concepts and variables tobe considered as causes in explaining the broad range of human behavior represented by crimeand criminal justice policy?
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45.Which type of research study project is designed to permit observations over an extendedperiod of time?
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46.Which of the following would be an example of a retrospective approach to longitudinal studies?
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47.A major mid-western university does annual surveys of its alumni. These surveys are designed togauge the attitudes that alumni hold about the university, its academic programs, and the majorteam sports. These surveys have been an annual event for the last two decades and representwhich type of study?
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48.In examining the relationship between drug use and crime discussed in your text, which of thefollowing represents an internal validity threat?
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49.When we specify what we mean by a concept we are using what?