Continuous scale
"Theoretically possible to divide any values of the scale
Height, depression"

Discrete scales
"Categorical values
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
DSM-4 diagnoses
Degree program"

Ordinal Scale
"Involve classifications like nominal scales but allow rank ordering
Olympian medalists
Likert scales"

Interval Scale
"Contain equal intervals between numbers. Each unit on the scale is equal to any other unit
IQ scores
Temperature"

Ratio Scale
"Interval scales with a true zero point. Zero represents something
Height & Weight
Reaction time"

Ordinal → Interval
Psychological disorders are naturally ordinal but are treated as interval.

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

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

J shaped curve
"Identify the type of distribution"
![J curve]

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