Psychology: Statistical Significance

Experimental Group

Participants in a group who receive the treatment level of the independent variable

Correlation Coefficient

A statistic that indicates the precise numerical relationship between two variables; r can range from -1.0 to +1.0 . A correlation of 0 indicates no relationship.

Null Hypothesis

A statistical assumption about the absence of an effect (typically, no difference between two values)

Effect Size

A calculated number that indicates the size of a difference between two values; not affected by sample size

Random Assignment

In an experiment, assigning participants to experimental and control conditions by chance, to minimize preexisting differences between the different groups

Error Bars

Lines that indicate the amount of variability or uncertainty around a point on a graph of research results

Inferential Statistics

Numbers that are calculated from a distribution of scores to provide evidence supporting or opposing a hypothesis

Descriptive Statistics

Numbers that are calculated from a distribution of scores, indicating the central tendency (average) and the variability (amount of scatter around the average).

p-level

The probability of finding a difference that is equal to or greater than what was actually measured, assuming that the null hypothesis is true; also called probability level. ** typically, if the p-level is less than 0.05 percent, the result is considered statistically significant

Population

A group of people (or animals) whose behavior is of interest to researchers. From this group, one or more samples are selected for measurement

Standard Deviation

A measure of variability, indicating how tightly the scores are clustered around the mean

Confidence Interval

A range of scores calculated such that there is a specific probability (usually .95) that the value of interest (such as the estimated mean of a population) actually falls within that range

Sample

A set of measurements from a group of people (or animals) selected from a larger population of interest

Hypotheses

A testable prediction, typically derived from a theory

Null Hypothesis Significance Testing (NHST)

An approach to evaluating research results that compares the observed outcome to what would be expected if the null hypothesis is true

Control Group

Participants in an experiment who do not receive the treatment

Statistical Significance

Whether a research result differs sufficiently from what would be expected from chance alone, due to random variations in behavior. A result is statistically significant if there is a low probability that the result is as due to chance factors.