Psychometric Terms

Correlation

The degree to which two sets of data are linked together

Decile

Any of the nine values that divide the sorted data into ten equal parts, so that each part represents 1/10 of the sample or population

Distribution

How data is spread out

False Negative

Given a result of negative when it should be positive.

False Positive

Given a result of positive when it should be negative.

Frequency Distribution

values and their frequency (how often each value occurs)

Mean

the average

Median

the middle of a sorted list of numbers

Mode

the most frequently occurring number in a set of numbers

Percentile

the value below which a percentage of data falls

Predictor

Other variables in the experiment that affect the response

Regression to the mean

phenomenon where if one sample of a random variable is extreme, the next sampling of the same random variable is likely to be closer to its mean, can mistakenly appear as meaningful change over time

Nominal scale

does not really have any evaluative distinction, one value is really not any greater than another (i.e. sex)

Ordinal scale

type of measurement scale used in market research that categorizes data into finite number of ordered levels or rankings. With ordinal scales, we only know that 2 is better than 1 or 10 is better than 9; we do not know by how much

Interval scale

Gives information about more or betterness as ordinal scales do, but have an equal distance between each value

Standard deviation

a measure of how spread out numbers are, measured by taking the mean, taking the distance of each value from the mean, squaring, adding them together, then taking the mean of that

Standard error of measurement

a statistical value that estimates how much an individual's observed test score might fluctuate from their hypothetical "true" score due to random error

True negative

Given a result of negative when it is in fact negative.

True positive

Given a result of positive when it is in fact positive.

Variance

A measure of how spread out numbers are

Z-score

How many standard deviations a value is from the mean