We might even create subgroups for gender. 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. Findings are drawn from whatever fits into the frame. Think of it in terms of taking a snapshot. The defining feature of a cross-sectional study is that it can compare different population groups at a single point in time. We would not influence non-walkers to take up that activity, or advise daily walkers to modify their behaviour. 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. This means that researchers record information about their subjects without manipulating the study environment. A cross-sectional study is an observational one.
