Attrition
A threat to internal validity caused by differential dropout rates across conditions.
Bar graph
A graph for nominal or ordinal data where bars do not touch, representing discrete categories.
Between-subject design
An experimental design where different participants are assigned to each condition.
Central tendencies
A statistical measure to determine a single score that defines the center of a distribution. The goal is to find the single score that is most typical or representative of the entire group.
Cluster Sampling
A probability sampling method where entire groups (clusters) are randomly selected, and all members of the selected groups are used.
Cohen’s d
A measure of effect size that expresses the difference between two group means in standard deviation units.
Continuous variable
A variable for which there are an infinite number of possible values between any two observed values (e.g., height, time).
Convenience Sampling
A non-probability sampling method where available and willing participants are selected.
Correlational Design
A non-experimental design that examines the associations between variables as they naturally occur, without manipulation.
Cronbach’s Alpha
A measure of internal consistency reliability, indicating how well items within a scale measure the same construct.
Cumulative Frequency (cf)
The sum of the frequencies at a particular score plus all the frequencies below it.
Dependent Variable
The variable that is the measured outcome in a study.
Descriptive Stats
Statistical procedures used to summarize, organize, and simplify data.
Discrete Variables
A variable consisting of separate, indivisible categories. No values can exist between two neighboring categories.
Effect Size
A measure of the magnitude of a research finding, indicating how large the effect is.
Experimental Design
A research design characterized by random assignment, manipulation of an independent variable, and control of extraneous variables, allowing for causal inference.
External Validity
The degree to which the results of a study can be generalized to other participants, settings, and times.
Frequency (f)
The count of scores in each category of a measurement scale.
Frequency Distribution
An organized tabulation showing the number of individuals located in each category on the scale of measurement.
Frequency Polygon
A graph for interval or ratio data where dots are placed above the center of each interval and connected by lines to show the shape of the distribution.
Histogram
A graph for interval or ratio data where the height of each bar corresponds to the frequency and the width corresponds to the real limits of the score, with bars touching.
History
A threat to internal validity where external events occurring between measurements affect the outcomes.
Hypothesis Testing
A statistical framework for using sample data to evaluate a hypothesis about a population.
Independent Variable
The variable that is manipulated by the researcher.