Your Easy Guide to Clinical Studies

Two terms are used when describing a study population:

• The target-population (i.e. sometimes referred to as “population”) represents a group of individuals of interest to the study (e.g. persons with lung cancer, aged between 18 and 50 years, diagnosed in 2020, and treated in Switzerland) 
• The studied-population: it is often not feasible to include all individual from a target-population in a study. The studied-population is therefore a sample from the larger target-population, and from whom study data is being collected

Individuals from the studied-population are identified as part of the larger target-population, as they fulfil the required inclusion and exclusion criteria, and are expected to be representative of the larger target population. Only results obtained from studied populations that accurately reflect the characteristics of the target-population can be extrapolated and assumed valid for the larger target-population

As a SP-INV:

• Define your target-population (e.g. non-smoking adults diagnosed with lung cancer living in Switzerland)
• Specify the inclusion/exclusion criteria of your study:
  • Inclusion: age range 18 – 50, with lung cancer diagnosed in 2020
  • Exclusion: any smoking within 5 years prior to diagnosis, living outside of Switzerland
• Define and discuss with a statistician an appropriate sampling strategy with the aim to  minimize potential selection bias

The ability to get a representative selection of individuals from the target-population is not always straightforward. Selection-biases might cause a studied-population to not accurately represent the target-population and hence, lead to biased or misleading results.

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References

ICH Topic E9 statistical Principles for Clinical Trials – see in particular

• 2.2.1 Population

ICH Topic E8(R1) on general considerations for clinical studies - see in particular

• 5.5 Methods to reduce bias