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.
Imputed Response
A missing survey response that is filled in by the data analyst. The method to fill in the missing response is based on careful analysis of patterns of missing data. Imputation is done to allow for statistical analysis of surveys that were only partially completed.
In-depth Interviewing
A research method in which face-to-face interviews with respondents are conducted using open-ended questions to explore topics in great depth. Questions are often customized for each interview, and topics are generally probed extensively with follow-up questions.
Independence
The lack of a relationship between two or more variables. For example, annual snow fall and the Yankee's season record are independent, but annual snow fall and coat sales are not independent.
Independent and Identically Distributed (IID)
A collection of two or more random variables {X1, X2, . . . , } is independent and identically distributed if the variables are independent and also have the same probability distribution.
Independent Variable
The variable that the researcher expects to be associated with an outcome of interest. For example, if a researcher wants to examine the relationship between parental education and children's language development, parent education (years of schooling or highest level of education completed) is the independent variable. Sometimes this variable is referred to as the treatment variable or the causal variable.
Index
A type of composite measure (i.e., a measure that is created from more than one data item, such answers to a series of survey questions) that summarizes responses to several specific observations (e.g., items on a parent questionnaire that ask whether their child participates in a variety of extracurricular activities) and represents a more general dimension (e.g., extracurricular activities might include music and dance lessons, different sports, and youth clubs). An index is often created by simply summing the responses to a series of yes/no questions.
Index Variable
A variable that is a summed composite of other variables that are assumed to reflect the same underlying construct. For example, a count of the number of caregiving activities (e.g., bathing and feeding) a father engages in with his infant child.
Indicator
An observation or measure that is assumed to be evidence of the attributes or properties of some phenomenon. Indicators are monitored over time and are used to assess progress toward the achievement of intended outcomes, goals, and objectives. Child well-being indicators include children's letter knowledge, frequency of pro- and anti-social behaviors, being read to on a regular basis by family members and attending high quality early childhood program.
Indicator Variable
In statistics, an indicator variables has only two possible values, which are typically coded 0 and 1 to identify the presence (1) or absence (0) of a characteristic. Some examples would include high school graduate (yes/no), preschool enrollment (enrolled, not enrolled), and program type (publicly funded/private). Also referred to as a dummy variable and are often used in regression analysis.
Indirect Effect
A condition where one variable affects another indirectly through an intervening variable. For example, parental income may have an indirect effect on children's school readiness skills if income affects the quality of child care a child receives which in turn affects the child's early reading, math and social skills. Also referred to as mediation.