The following chapter is excerpted from Designing HIV/AIDS Intervention Studies: An Operations Research Handbook, Andrew Fisher and James Foreit, 2002, Washington, DC: Population Council. (More on OR Handbook)
A fter formulating the study objectives and hypotheses and describing fully the study intervention, the next step in the research process is to define operationally the key variables and terms of the study. Operational definitions serve two essential purposes: (1) They establish the rules and procedures the research investigator will use to measure the key variables of the study, and (2) they provide unambiguous meaning to terms that otherwise might be interpreted in different ways. Every research proposal must include operational definitions of major variables and terms.
Operational Definitions of Variables
Suppose that a dependent variable of a study is knowledge about how HIV/AIDS is transmitted. Before this variable can be measured, it is necessary first to establish the operational procedures that specify how the measurement will be made and at the same time define what the researcher means by the words “knowledge about how HIV/AIDS is transmitted.” This variable must be defined in terms of events that are observable by the senses and therefore measurable.
The observable events serve as an indicator of the variable, knowledge about HIV/AIDS transmission. Alone and by itself, knowledge is not observable by the senses. It is an abstract concept. You cannot touch knowledge, see it, smell it, taste it, or hear it. What is needed is an observable event that can be measured and that indicates knowledge. Usually, such an indicator of knowledge in an HIV/AIDS study is based on a series of questions. For example, you might ask a respondent, “Do you know how a person can become infected with AIDS?” “Please list all the ways you know a person can get AIDS.” “Can a person get AIDS from a mosquito bite?” “Can HIV/AIDS be transmitted through a mother’s breast milk?” Each of these questions indicates whether the respondent knows about certain aspects of HIV/AIDS transmission. Asking a question and hearing a response is an observable event that can be measured. A research study might ask ten HIV/AIDS knowledge questions. Each time a respondent gives an answer that indicates knowledge about HIV/AIDS transmission, the researcher could record a score of one. Every time an answer is given that does not indicate knowledge about HIV/AIDS transmission, the researcher could record a score of 0. For each respondent, the researcher could then add the total number of correct answers to the ten questions and create a HIV/AIDS knowledge score. This score would range from 0 correct answers to ten correct answers. Persons with a score of 0 would be operationally defined as having no knowledge about HIV/AIDS transmission. Persons with a score of ten would be operationally defined as having a high level of knowledge about HIV/ AIDS transmission. In your research proposal, the operational definition of knowledge might appear as: Knowledge about HIV/AIDS transmission
This is not the only way the variable could be defined operationally. You might wish to establish categories of HIV/AIDS knowledge, distinguishing between those respondents who have high HIV/ AIDS knowledge, medium knowledge, low knowledge, and no knowledge. Each of these levels is a category of the variable, and each category requires an operational rule that tells you how to assign any given respondent to the category. One way of operationally defining the categories might be as follows: High knowledge
Correct responses to eight or more of the ten questions. Correct responses to between four and seven of the ten questions.
Correct responses to between one and three of the ten questions. No correct answers to any of the ten...