In nearly every clinical trial or observational study, the researchers provide the baseline characteristics of the study participants in Table 1. This table will include any demographics the researchers recorded — age, geography, insurance status, income status, race/ethnicity, etc. — and any other characteristics that were relevant to the recruitment or randomization of the participants, such as comorbidities, severity of disease or prior exposure to a treatment.
Deeper dive
In a randomized controlled trial, Table 1 ideally has no statistically significant differences between groups, and it’s worth skimming it to see if any differences do exist. If they do, the authors should address it in their methods and/or limitations section. In observational trials, some statistically significant differences between groups may be unavoidable, depending on the populations, recruitment methods and what’s being studied, but the authors should still address how they adjust for these differences in their methods and/or limitations. Table 1 is also useful for seeing what ISN’T there — what characteristics/baseline data did the authors not collect or consider that they should have or that might have confounded the results?
Another time it may be important to look at Table 1 is in meta-analyses or systematic reviews where individual populations across trials might be quite different. Reviews/meta-analyses do not always include a Table 1 of participants across trials, but they should at least address how homogenous or heterogenous the study populations were and the potential significance of those differences.