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.
Skewness
The tendency of the distribution of a statistic to depart from symmetry. Distributions can be skewed with more values to the right (positive) or to the left (negative). When the distribution is skewed, the median is a better measure of the midpoint of the distribution than the mean.
Slope
The coefficient of the independent variable indicating the change in dependent variable per unit change in the independent variable.
Snowball Sampling
A strategy used to gather a sample for a research study in which study participants give the researcher referrals to other individuals who fit the study criteria. Snowball samples cannot be generalized to the population because they are not selected randomly. Snowball samples are usually used to investigate groups that have some unique, rare, or unusual quality and groups where members know each other through an organization or common experience. For example, snowball samples might be used to identify parents who homeschool their children and attend local support groups.
Social Desirability
The tendency for respondents to give answers that are socially desirable or acceptable, but may not reflect their actual attitudes or behavior.
Social Network Analysis
Social network analysis (SNA) is the process of investigating social structures by mapping and measuring the relationships between people individually or in groups. Some examples of SNA include the study of friendship and acquaintance networks, family networks, and service delivery networks. SNA provides both a visual and a mathematical analysis of human relationships.
Sociogram
A display of networks of relationships among variables, designed to enable researchers to identify the nature of relationships that would otherwise be too complex to understand well enough to be able to describe.
Spurious Relationship
A statistical association between two variables that is produced by a third variable rather than by a causal link between the two original variables. For example, American children start school at the same time of year that the leaves begin to fall from the trees. This does not mean that leaves falling from trees affects when children start school or vice versa, instead both leaves falling from trees and children starting school occur during autumn.
Standard Deviation
A measure of variability or dispersion of a set of data. The standard deviation (SD) is the square root of the variance. It is calculated based on the difference between each individual observation and the mean observation.
Standard Error
A measure of the extent to which the sample mean fluctuates. The standard error is the standard deviation (SD) of the sample means. Conceptually, the standard error of the mean would be calculated by selecting multiple samples at random from a population, calculating the mean for each of the samples, then calculating the standard deviation of these sample means. Because only one sample is generally drawn from a population for a research study, the standard error is calculated by dividing the sample deviation by the number of the observations in the sample. Generally speaking, the larger the sample, the smaller the standard error.
Standard Score
An indicator of the relative standing of a score within a normal distribution of scores, defined by its mean and standard deviation. It is calculated by subtracting the mean score from each score and dividing by the standard deviation of the scores in the distribution. The standard score, also known as the Z-score, tells us where a score lies in relation to the mean. Scores above the mean have a positive Z-score value and those below the mean have a negative value. Standard scores are used in norm-referenced assessment to compare one student's performance on a test to the performance of other students in the same age group or grade. Standard scores estimate whether a student's scores are above average, average, or below average compared to peers.