CH3: Statistics

Continuous scale

Theoretically possible to divide any values of the scale (e.g., height, depression).

Discrete scales

Categorical values (e.g., male or female).

Error

Collective influence of all factors on a test score beyond those specifically measured by the test.

Nominal Scales

Involve classification or categorization based on one or more distinguishing characteristics (e.g., DSM-4 diagnoses, degree program).

Ordinal Scale

Involve classifications like nominal scales but allow rank ordering (e.g., Olympian medalists, Likert scales).

Interval Scale

Contain equal intervals between numbers; each unit on the scale is equal to any other unit (e.g., IQ scores, temperature).

Ratio Scale

Interval scales with a true zero point; zero represents something (e.g., height & weight, reaction time).

Ordinal, Interval

Psychological disorders are naturally _ but are treated as _

Distributions

A set of test scores arrayed for recording or study.

Raw score

Straightforward, unmodified accounting of performance, usually represented by a number.

Histogram

A graph with vertical lines drawn at the true limits of each test score forming a series of contiguous rectangles.

Y-axis, X-axis

In a Bar graph, numbers of indicative frequency appear on the _ and reference to some categorization appears on _

J shaped curve

Identify the type of distribution.

Bimodal distribution

Identify the type of distribution

Positively skewed distribution

Identify the type of distribution.

Negatively skewed distribution

Identify the type of distribution.

Rectangular distribution

Identify the type of distribution.

Central Tendency

A statistic that indicates the average or midmost score between extreme scores in a distribution.

Mean

Sum of observations divided by the number of observations.

Median

Middle score in a distribution.

Mode

Most frequently occurring score in a distribution.

Variability

Indication of the degree to which scores are scattered or dispersed in a distribution.

Range

Difference between the highest and lowest scores.

Interquartile range

Difference between 3rd and 1st quartile.

Semi-Interquartile Range

Interquartile range divided by 2.

Variance

Arithmetic mean of the squares of the differences between the scores in a distribution and their mean.

Standard deviation

The square root of the average squared deviations about the mean.

Kurtosis

Steepness of a distribution in the center.