PY 211: Chapter 1

For students in Gayle Faught's statistics class. Compatible with Statistics for Psychology published by Pearson.

Statistics

A branch of mathematics that focuses on the organization, analysis, and interpretation of a group of numbers.

Descriptive Statistics

Procedures for summarizing a group of numbers or otherwise making them more understandable.

Inferential Statistics

Procedures for drawing conclusions based on the numbers collected in a research study but going beyond them.

Variable

A characteristic that can have different values.

Value

The possible number or category that a score can have (just a number).

Score

A particular person’s value on a variable.

Numeric Value

Variable whose values are numbers (a.k.a quantitative variable).

Equal-Interval Variable

Variable in which the differences between adjacent numbers stand for approximately equal amounts of what is being measured.

Rank-Order Variable

Numeric variable in which the values are ranks such as places in a race (a.k.a ordinal variable).

Nominal Variable

Variable with values that are categories (a.k.a categorical variable).

Levels of Measurement

Types of underlying numerical information provided by a measure.

Discrete Variable

A variable that has specific values and that cannot have values between these specific values.

Continuous Variables

Variable for which, in theory, there are an infinite number of values between any two values.

Frequency Table

An ordered listing of the number of individuals having each of the different values for a particular variable.

Interval

The range of values in a grouped frequency table that are grouped together.

Grouped Frequency Table

A frequency table in which the number of individuals (frequency) is given for each interval of values.

Histogram

A bar-like graph of a frequency distribution in which the values are plotted along the horizontal axis and the height of each bar is the frequency of that value.

Frequency Distributions

A pattern of frequencies over the various values of a given variable; a graph that represents the values taken from a frequency table.

Unimodal Distribution

A frequency distribution with one value clearly having a larger frequency than any other.

Bimodal Distribution

A frequency distribution with two approximately equal frequencies, each clearly larger than any of the others.

Multimodal Distribution

A frequency distribution with two or more high frequencies separated by a lower frequency.

Rectangular Distribution

A frequency distribution in which all values have approximately the same frequency.

Symmetrical Distribution

A distribution in which the pattern of frequencies on the left and right side are mirror images of each other.

Skewed Distribution

A distribution in which the scores pile up on one side of the middle and are spread out on the other side.

Positively Skewed

Distribution that is skewed to the right.

Negatively Skewed

Distribution that is skewed to the left.

Floor Effect

A situation in which many scores pile up at the low end of a distribution because it is not possible to have any lower score.

Ceiling Effect

A situation in which many scores pile up at the high end of a distribution because it is not possible to have any lower score.

Normal Curve

Specific, math-defined, bell-shaped distribution that is symmetrical and

Kurtosis

The extent to which a frequency distribution deviates from a normal curve in terms of whether its curve in the middle is more peaked or flat than the normal curve.