Zielpopulation

Zielpopulation, or target population, is a term used in research to denote the group of individuals or units to whom the results of a study are intended to apply. It is defined by predefined characteristics such as age, sex, health status, geographic location, and time frame. The Zielpopulation is used to frame the study objectives, design, and the interpretation of external validity.

It is important to distinguish the Zielpopulation from the accessible population and from the actual sample. The Zielpopulation represents the ideal or intended group for inference. The accessible population is the subset of the Zielpopulation that investigators can contact and recruit within practical constraints. The sample is the actual set of participants selected from the accessible population. The quality of generalization depends on how well the sampling method represents the Zielpopulation.

Defining the Zielpopulation typically involves inclusion and exclusion criteria. Inclusion criteria specify the characteristics required for participation (for example, adults aged 18–65 with a diagnosed condition in a specified country). Exclusion criteria remove individuals with conditions that could confound results or pose safety concerns. Clear criteria support reproducibility and appropriate generalization.

Examples illustrate the concept. A clinical trial of a new antihypertensive drug might target adults aged 40–65 with stage 1 hypertension in the United States. A survey on dietary habits might target residents of urban areas aged 18–75 who are responsible for household meals.

Application and challenges. Defining the Zielpopulation requires alignment with research aims and feasibility. Poor alignment or overly broad criteria can threaten external validity; overly narrow criteria can limit generalizability and recruitment. Researchers strive to document the definition and the reasoning behind it to enable interpretation and replication.