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.
Random Effects Model
A random effects model is a statistical model (e.g., regression or analysis of variance) that assumes the independent variable(s) are random. Used when the levels of the variable(s) in the data are a subset of all possible values of the variable(s) (e.g., household income and children's height and weight in inches and ounces). In contrast, a fixed effects model assumes that all the levels of the variable(s) of interest are in the data (e.g., children's race/ethnicity or sex).
Random Error
Error in measurement that is due to factors that cannot not be controlled. Random errors are always present and are unpredictable. Sources of random error in measurement include fluctuations in the values obtained by an instrument (e.g., small differences in children's weight when measured twice using the same scale) and changes in what is being measured.
Random Sampling
A sampling technique in which individuals are selected from a population at random. Each individual has a chance of being chosen, and each individual is selected entirely by chance.
Random Selection
Random selection refers to the process of selecting individuals (schools,programs, classrooms) from the population to participate in a study. In random selection, each individual is chosen by chance and has a fixed and known probability of selection into the study sample.
Random Variable
A variable that numerically measures some characteristic of a sample, or population (e.g., height). The value of the variable will differ depending on which individual is measured (i.e., people are of different heights). The variable is said to be random because the variation in the value of the variable is due, at least in part, to chance (i.e., some people are just taller than other people).
Randomization
Assigning individuals in a sample to either an experimental group or a control group at random.
Range
A measure of how widely the data (values) for a specific variable are dispersed or spread. The larger the range the more dispersed the data. The range is calculated by subtracting the value of the lowest data point from the value of the highest data point. For example, in a sample of children between the ages of 2 and 6 years the range would be 4 years. When reporting the range, researchers typically report the lowest and highest value (Range = 2 - 6 years of age).
Rank Order Scale
A set of behaviors, objects or statements presented to research subjects which they are asked to rank (put them in some order) according to a specific criterion (e.g., size, importance, frequency). For example, parents may be presented with a number of factors that may affect their choices of child care and asked to order them in their importance.
Rating Scale
A rating scale is a measuring instrument for which judgments are made in order to rate a subject or case at a specified scale level with respect to an identified characteristic or characteristics.
Ratio
A ratio is a relationship between the number in two groups of objects. It tells us how many times the number in the first group contains the number in the second group. For example, if we have a 10 elementary schools and 3 middle schools in a community, the ratio of elementary to middle schools is 10 to 3 (10:3), or roughly 3 elementary schools to every 1 middle school.