The research glossary defines terms used in conducting social science and policy research, for example those describing methods, measurements, statistical procedures, and other aspects of research; the child care glossary defines terms used to describe aspects of child care and early education practice and policy.
Control Group
In an experiment, the control group does not receive the intervention or treatment under investigation. This group may also be referred to as the comparison group.
Control Variable
A variable that is not of interest to the researcher, but which interferes with the statistical analysis. In statistical analyses, control variables are held constant or their impact is removed to better analyze the relationship between the outcome variable and other variables of interest. For example, if one wanted to examine the impact of education on political views, a researcher would control income in the statistical analysis. This removes the impact of income on political views from the analysis.
Controlled Experiment
A form of scientific investigation in which one variable, termed the independent variable, is manipulated to reveal the effect on another variable, termed the dependent or responding variable, while all other variables in the system are held fixed.
Convenience Sampling
A sampling strategy that uses the most easily accessible people (or objects) to participate in a study. This is not a random sample, and the results cannot be generalized to individuals who did not participate in the research.
Cooperation Rate
In survey research, this is the percentage of persons who answer a survey or complete an interview out of all persons who were contacted and asked to complete the survey or interview.
Correlation
The degree to which two variables are associated. Variables are positively correlated if they both tend to increase at the same time. For example, height and weight are positively correlated because as height increases weight also tends to increases. Variables are negatively correlated if as one increases the other decreases. For example, number of police officers in a community and crime rates are negatively correlated because as the number of police officers increases the crime rate tends to decrease.
Correlation Coefficient
A measure of the degree to which two variables are related. A correlation coefficient in always between -1 and +1. If the correlation coefficient is between 0 and +1 then the variables are positively correlated. If the correlation coefficient is between 0 and -1 then the variables are negatively correlated.
Covariate Balance
In randomized experiments, randomization creates covariate balance between the treatment (or treatment and control) groups. In such experiments, the characteristics of participants in the different groups are approximately equal. In observational studies (studies using nonexperimental designs) the characteristics of participants in different groups will rarely be equal (covariate unbalance). Researchers use different methods to achieve covariate balance when using observational data to test for treatment or causal effects (for example, propensity scores).
Coverage
Coverage reflects the extent to which all elements on a sampling frame (list) are members of the population to be sampled, and the extent to which every element in that population appears on the frame (list) once and only once. For example, the extent to which a list of child care providers includes (covers) all the providers in a given location (state, community).
Critical Incident Technique
A qualitative research method that collects observations or participant reports of behaviors that have critical significance. The observations or reports are recorded and tracked over a period of time. Observations/reports are placed into categories, summarized, and counted and used to solve practical problems and develop broad theories of human behavior.