National Information Center on Health Services Research and Health Care Technology (NICHSR)
Measurement is the process of specifying and operationalizing a given concept. A research instrument contains the operational definitions of all measures related to the research and is primarily used to collect data. When a research instrument contains only questions and statements to be answered by respondents, it is called a questionnaire. from Shi L. Health services research methods. New York: Delmar; 1997. 410 p.