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a branch of mathematics that involves the collection, analysis, and organization of data

descriptive statistics

procedures used to summarize data

inferential statistics

procedures used to analyze data after an experiment is completed in order to determine whether the IV had a significant effect


the assignment of symbols to events according to a set of rules

scale of measurement

a set of measurement rules

nominal scale

a scale in which the events are assigned to categories (i.e. left-handed vs right-handed)

ordinal scale

a scale that permits events to be rank ordered without necessarily having equal distance between points

interval scale

a scale that permits rank ordering with the assumption of equal intervals between adjacent events (no true zero)

ratio scale

a scale of measurement that permits rank ordering, equal distance, and a true zero point


the score that occurs most often


the number that divides a distribution in half


the mathematical average

pie chart

graphical representation of the percentage allocated to each alternative as a slice of a circular pie


A graph of vertical bars representing the frequency distribution of a set of data, the bars touch, generally intervals

bar graph

a graph in which the frequency of each category of a qualitative variable is represented as a vertical column, bars do not touch.

frequency polygon

type of line graph that shows frequency distributions; made by placing a dot on each bar of a histogram, connecting the dots, and removing the bars

line graph

a graph that uses line segments to show how data changes


vertical or y-axis of a graph


horizontal or x-axis of a graph


the extent to which scores are spread out around the mean


a measure of variability that is computed by subtracting the smallest score from the largest score


a single number that represents the total amount of variation in a distribution, also the square of the standard deviation

standard deviation

square root of the variance, has important relations to the normal curve

normal distribution

a symmetrical, bell-shaped distribution having half the scores above the mean and half the scores below the mean (bell curve)

correlation coefficient

a single number representing the degree of relation between two variables

null hypothesis

the claim that the relationship proposed between two variables does not exist, or that the difference in data was due to chance (not the operation of the IV)

t test

an inferential statistical test used to evaluate the difference between two means

degrees of freedom

the ability of a number in a specified set to assume any value

type I error

accepting the experimental hypothesis when the null hypothesis is true

type II error

accepting the null hypothesis when the experimental hypothesis is true

effect size

the magnitude or size of the experimental treatment

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