Psychology Statistics

Sampling Error

Naturally occuring discrepancy between a sample statistic and the corresponding population parameter

Construct

Internal attribute that cannot be directly observed but is useful for describing and explaining behavior

Operational Definition

Procedure for measuring external behavior wherein the resulting measurements measure a hypothetical construct

Continuous Variable

Value which is divisible into an infinite number of fractional parts

Real Limit

Boundary of intervals for scores that are represented on a continuous number line

Upper Real Limit

Boundary at the top of the interval

Discrete Variable

Value consisting of separate, indivisible categories, wherein no values can exist between two neighboring categories

Lower Real Limit

Boundary at the bottom of the interval

Nominal Scale

Set of categories that have different names

Ordinal Scale

Set of categories that are unorganized in an ordered sequence

Experimental Method

Manipulating one variable while another variable is observed and measured

Control Condition

Group that either recieves no treatment or receives a neutral, placebo treatment

Experimental Condition

Group that receives the experimental treatment

Nonequivalent Groups Study

Score comparison method where the researcher does not control which participants go into which group

Quasi-independent Variable

Value that is used to create the different groups of scores

Pre-post Study

Method of using the passage of time to create the groups of scores

Statistics

Value that describes a sample, usually derived from measurements of the individuals in the sample

Descriptive Statistic

Procedure used to summarize, organize, and simplify data

Sample

Set of individuals selected to represent the population in a research study

Data Set

Collection of measurements or observations

Data

Measurements or observations

Inferential Statistics

Technique that allows one to make generalizations about the populations from which samples were selected

Symmetrical Distributions

Distribution in which one side is a mirror image of the other

Postiive Skew

Distribution wherein the tail points toward the right end of the X-axis

Negative Skew

Distribution wherein the tail points toward the left end of the X-axis

Frequency Distribution

Organized tabulation showing number of individuals located in each category on the scale of measurement

Grouped Frequency Distribution Table

Table presenting groups of scores rather than individual values

Class Interval

Group of scores in a grouped frequency distribution table

Apparent Limit

Value that appears to form the upper and lower boundaries for the class interval

Histogram

Graph with a bar drawn above each score and with no space between adjacent bars

Polygon

Graph with a dot centered above each score according to the frequency of each score

Bar Graph

Diagram with a rule drawn above each score with spaces left between adjacent bars

Relative Frequency

Estimated number of occurrences of score

Skewed Distribution

Graph in which scores pile up toward one end of the scale and taper off

Tail

Distribution section where scores taper off toward one end of a distribution

Mean

For distribution is the sum of the scores divided by the number of scores

Median

Midpoint in a list of scores listed in order from smallest to largest

Population Mean

Formula where in all scores in the population are added, and then divided by N

Sample Mean

Formula with symbols to signify population subset values

Weighted Mean

Formula combining multiple sets of scores and dividing to find overall mean for combined group

Central Tendency

Statistical measure to determine a single score that defined the midpoint of a distribution

Mode

Score or category that has the greatest frequency in a frequency distribution

Bimodal

Distribtuion with two scores with greatest frequency

Multimodal

A distribution with more than two scores with greatest frequency

Major Mode

Taller peak when two scores with greatest frequency have unequal frequencies

Minor Mode

Shorter peak when two scores with greatest frequency have unequal frequencies

Line Graph

Diagram used when values on horizontal axis are measured on an interval or ratio scale

Sample Variance

Population Variance

Population Standard Deviation

Sample Standard Deviation