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.
Stratified sampling
A type of probability sample where the units in a population of interest are divided into mutually exclusive and collectively exhaustive groups or strata. A probability sample (e.g., simple random sample) is then drawn from each stratum. Stratified sampling provides greater precision than a simple random sample of the same size. It is also used to ensure representation of different groups (e.g., programs in different regions of the country) in the sample.
Stratified Sampling
A statistical method for testing different theorized models, including the "structures" of relationships among the observed indicators and their underlying concepts.
Structural Model
A theoretical model assumed to underlie the data that expresses the relationship between the dependent variable and the independent variables.
Structured Interview
The interviewer asks respondents the same questions using a predetermined series of interview questions. Deviations from the predetermined series of questions are not allowed in the interview process.
Structured Observation
Structured observation (or systematic observation) is a data collection method in which researchers gather data by observing the actions of individuals alone or during interactions with others. Research specifies in advance which behaviors are to be observed and how they are to be classified. Observers typically note the occurrence and frequency of the behaviors. Structured observations often are conducted in laboratory settings, but can be done in natural settings (e.g., children's homes) as well.
Subjectivity
A reflection of the person's mind, or thoughts, which is the result of his/her experiences, moods or attitudes.
Subjects
Those who participate in research and from whom data are collected.
Subsample
A sample selected from a larger sample. Subsamples are often selected to control data collection costs. For example, in a longitudinal study, the original (larger) sample may be divided into groups based on the per unit cost of data collection and a subsample (smaller sample) of high cost units (e.g., cases that have been difficult to complete in prior rounds or cases that entail high travel costs) selected.
Survey Research
A research approach designed to systematically collect data about a group of individuals. Data are obtained through direct questioning, using a written questionnaire (e.g., mail and online surveys) or interview (e.g., phone and in-person interviews). Data can be collected at a single point in time (cross-sectional survey) or from the same participants at multiple time points (longitudinal survey). While survey research most often involves collecting data from a sample of the population, population surveys or census surveys use survey methods (e.g., questionnaires, interviews).
Systematic Bias
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.