Source population and sampling

Aim

To obtain a representative sample appropriate to the research question.

 

Requirements

Documentation of the recruitment of the subjects including responders and non-responders.

 

Documentation

Flow chart of the inclusion and exclusion of the subjects.

 

Responsibilities

Executing researcher:
  • Clearly describe the domain including inclusion and exclusion criteria.
  • Document the selection of the sample.
  • Document the recruitment of the subjects including responders and non-responders.
  • Document the reasons for non-participation.
Project leaders: To advice the executing researcher in respect of:
  • Draw the source population;
  • Identification of the source population;
  • Select a sample from the identified study population.
Research assistant: Ask reasons for non-participation.

 

How To

Epidemiological research implies conducting measurements on people and deriving estimates from this. A good sample from a well-described study population prevents you from bias in the final results and, therefore, ensures you to be able to generalize the study outcomes.
Three steps need to be completed in specifying a study population:
  1. Draw the source population: Describe to which group of people you want the study results to apply to (referring to your research question).
  2. Identification of the source population: Select the individuals who could be involved in the study, by describing detailed inclusion and exclusion criteria.
  3. Select a sample from the study population: A random sample will be selected from the study population. In a patient-control study, both the patients and controls need to be selected from the same source population. The sample size is based on power calculations, which should be taken into account the expected non-response and dropouts.
Once the study population has been established, individuals from the sample will be invited to participate in the research. An important principle in medical research is that participation should always be voluntary and individuals should only be bothered a limited number of times with invitations to participate. When individuals do not want to participate or do not response to the invitation, this should be documented as ‘non-response’. It is advised to ask the non-responders what their reason is for non-participation. Document these reasons and, if possible, their characteristics.

 

Audit questions

  1. Have the domain, source population and study population been documented?
  2. Have the steps been documented why this specific study population was selected?
  3. How was sampling undertaken?
  4. How many people refused to participate? Have the reasons for refusal been documented?

 

V2.0: 12 May 2015: Revision format
V1.1:  1 Jan 2010: Translation into English
V1.0:  21 April 2004