Glossary

Coefficient of correlation: A number that represents the direction and strength of a correlation.

Coefficient of determination: The percentage of variation accounted for in one variable by knowing the value of another variable.

Correlational statistics: Statistics that determine the relationship between two variables.

Dependent variable: The variable assessed by the experimenter to determine whether there is a difference due to the independent variable.

Descriptive statistics: Statistics that summarize research data.

Frequency distribution: A list of the frequency of each score or group of scores in a set of scores.

Frequency histogram: A graph that displays the frequency of scores as bars.

Frequency polygon: A graph that displays the frequency of scores by connecting points representing them above each score.

Independent variable: Typically a variable of interest which the experimenter manipulates.

Inferential statistics: Statistics used to determine whether changes in a dependent variable are caused by an independent variable.

Line graph: A graph used to plot data showing the relationship between independent and dependent variables in an experiment.

Mean: The arithmetic average of a set of scores.

Median: The middle score in a set of scores that have been ordered from lowest to highest.

Mode: The score that occurs most frequently in a set of scores.

Negative skew: A graph that has scores bunching up toward the positive end of the abscissa.

Normal curve: A bell-shaped graph representing a hypothetical frequency distribution for a given characteristic.

Normal distribution (bell-shaped curve): This graph shows the normal distribution of IQ scores as measured by the Wechsler Adult Intelligence Scale. The normal distribution is a type of bell-shaped frequency polygon in which most of the scores are clustered around the mean. The scores become less frequent the farther they appear above or below the mean.

Null hypothesis: The prediction that the independent variable will have no effect on the dependent variable in an experiment.

Pearson’s product-moment correlation: Perhaps the most commonly used correlational statistic.

Percentile: The score at or below which a particular percentage of scores fall.

Pie graph: A graph that represents data as percentages of a pie.

Positive skew: A graph that has scores bunching up toward the negative end of the abscissa.

Range: A statistic representing the difference between the highest and lowest scores in a set of scores.

Scatter plot: A graph of a correlational relationship.

Standard deviation: A statistic representing the degree of dispersion of a set of scores around their mean.

Statistical significance: A low probability (usually less than 5 percent) that the results of a research study are due to chance factors rather than to the independent variable.

Statistics: Mathematical techniques used to summarize research data or to determine whether the data support the researcher’s hypothesis.

Variance: A measure of variability indicating the average of the squared deviations from the mean.