A summary of how often various scores occur in a sample of scores. Score values are arranged in order of magnitude, and the number of times each score occurs is recorded.

A symmetrical distribution forming a bell-shaped curve in which the mean, median, and mode are all equal and fall in the exact middle.

A finding that two factors vary systematically in opposite directions, one increasing as the other decreases.

The sum of a set of scores in a distribution divided by the number of scores; the mean is usually the most representative measure of central tendency.

Failing to find a significant effect that does, in fact, exist.

A measure of variability; the highest score in a distribution minus the lowest score.

The score that divides a frequency distribution exactly in half so that the same number of scores lie on each side of it.

A measure of variability; expressed as the square root of the sum of the squared deviations around the mean divided by the number of scores in the distribution.

A graph that represents the relationship between two variables.

Mathematical methods used to determine how likely it is that a study’s outcome is due to chance and whether the outcome can be legitimately generalized to a larger population.

An asymmetrical distribution; more scores occur on one side of the distribution than on the other. In a positively skewed distribution, most of the scores are low scores; in a negatively skewed distribution, most of the scores are high scores.

A single number that presents information about the spread of scores in a distribution.

Mathematical methods used to organize and summarize data.

The relationship between two variables.

A finding that two factors vary systematically in the same direction, increasing or decreasing together.

A way of graphically representing a frequency distribution; a type of bar chart that uses vertical bars that touch.

Test used to establish whether the means of two groups are statistically different from each other.

A distribution in which scores fall equally on both sides of the graph. The normal curve is an example of a symmetrical distribution.

A branch of mathematics used by researchers to organize, summarize, and interpret data.

Erroneously concluding that study results are significant.

A number, expressed in standard deviation units, that shows a score’s deviation from the mean.

A complete set of something—people, nonhuman animals, objects, or events.

A numerical indication of the magnitude and direction of the relationship (the correlation) between two variables.

A subset of a population.

A way of graphically representing a frequency distribution; frequency is marked above each score category on the graph’s horizontal axis, and the marks are connected by straight lines.

The most frequently occurring score in a distribution.

A single number that presents some information about the “center” of a frequency distribution.