Data collection

Data collection is the systematic gathering and recording of information for analysis, monitoring, or decision-making. It uses defined procedures to produce observations suited to a particular question or purpose.

Sampling (statistics): The selection of a subset of units from a population to estimate or describe the whole. Sampling rules decide which people, objects, or events contribute observations.
Unit of analysis: The entity about which a study makes observations or draws conclusions. Collection must identify whether each record represents a person, event, place, or other entity.
Census: A systematic enumeration of every member of a defined population. A census aims to cover the whole population rather than a selected sample.
Selection bias: Systematic distortion arising when inclusion in a study is related to characteristics being studied. Recruitment and sampling decisions can make collected observations unrepresentative.
Survey methodology: The study of designing surveys, selecting respondents, and collecting and analyzing survey responses. It turns questions and respondent selection into a structured collection procedure.
Variable (statistics): A characteristic that can take different values across observed units. Variables specify which characteristics the collection process records.
Clinical trial: A prospective study that assigns health interventions to participants to assess their effects. Trials use planned measurements and follow-up to collect outcome and safety data.
Observer bias: Systematic error caused by an observer’s expectations or judgments influencing recorded observations. Human recording can vary with expectations unless procedures limit subjective interpretation.
Measurement: The assignment of values or categories to attributes according to defined rules. A collection process needs consistent rules for turning attributes into recorded values.
Operationalization: The process of defining how an abstract concept will be observed or measured. It converts broad aims into concrete questions, indicators, or measurements.

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