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.
A scale where the number of favorable and unfavorable categories is not the same.
A statistic that is free of systematic bias. Systematic bias occurs when the recorded data from a sample is systematically higher or lower than the true data values within the population. Systematic bias can occur as a result of sampling bias or measurement bias. Sampling bias is an error in sampling when some subgroup of the target population is unintentionally left out of the sampling process. Measurement bias is an error in data collection when some occurrence distorts the responses in the same way (e.g., a test is administered in a noisy classroom). Bias is a serious error in data collection and should be handled through a researcher's careful attention to sources of bias.
Unconditional Longitudinal Models
When modeling change or growth over time and its relationship to one or more predictor variables, researchers first test several models that include either no predictors or that include only time as a fixed effect. These unconditional models are used to initially identify the amount of variation in the outcome variable and the variation in outcome growth rates that is due to interindividual differences.
Unequal Variances (Heteroscedasticity)
Heteroscedasticity refers to values on a variable (dependent) that are unequally spread (unequal variances) across the values on a second, predictor (independent) variable. Heteroscedasticity is the absence of homoscedasticity (equal variance in the dependent variable across values/levels of the independent variable), which is a key assumption of linear regression analysis.
Unfolding questions include a sequence of questions designed to yield more complete and accurate data than would a single question on the same topic. They are used by survey researchers in an attempt to reduce missing data and measurement error. For example, asking respondents who are unwilling or unable to provide their exact household a set of follow-up questions designed to identify within which of a narrower set of income categories their income falls has been shown to significantly reduce the amount of missing income data.
Unit of Analysis
The individuals, groups of people, or objects that are being analyzed in a study. For example, if an analysis examines children's well-being, children are the unit of analysis. If an analysis examines family income, families are the unit of analysis. For some analyses, classrooms (the mean quality of early childhood classrooms) and programs (percentage of programs offering before- and after-care) are the units of analysis.
Examination of the properties of one variable only and not the relationship between variables. Generally univariate analysis is performed by examining frequencies of response or values (counts and frequency distribution), one or more measures of central tendency (mode, mean and median) and the spread of responses or values (range, variance, standard deviation).
An interview in which the researcher asks open-ended questions. The researcher aims to give respondents the latitude to talk freely on a topic and to influence the direction of the interview. There is no predetermined plan about the specific information to be gathered from these types of interviews.