
Glossary
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 bellshaped graph representing a hypothetical frequency distribution for a given characteristic. Normal distribution (bellshaped 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 bellshaped 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 productmoment 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. 