Statistics in Psychology

Population

the entire group of interest.

Sampling Error

a naturally occurring discrepancy or error between a sample statistic and the corresponding population parameter.

Nominal Scale

a scale of measurement that consists of a set of categories that have different names

it labels and categorizes observations, but cannot make any quantitative distinctions between those observations.

only occasionally represented by numbers.

Ordinal Scale

a scale of measurement that consists of a set of categories that are organized in an ordered sequence.

it ranks observations in terms of size or magnitude

it shows a directional relationship between categories; can show the difference between 2 categories, but not the size of the difference.

Interval Scale

a scale of measurement that consists of ordered categories that are all intervals of exactly the same size.

as a rule, equal differences between numbers on a this scale reflect equal differences in magnitude.

has a point ‘0’ that is arbitrary and does not indicate a ‘0 amount’—or absence—of the variable being measured.

Ratio Scale

a scale of measurement that consists of an interval scale with the additional feature of an absolute 0 point.

as a rule, the ratios of the numbers do reflect ratios of magnitude.

nominal

A sample is given a packet of M&M’s and is told to randomly draw from the package. The frequency of each drawn candy is categorized by color. This example shows the _________ scale of measurement.

ordinal

A sample is asked to share the various t-shirt sizes they prefer and the results are collected and organized by increasing size. This example shows the _________ scale of measurement.

interval

A sample is measured for their individual body heat levels in degrees Celsius. When collecting the measurements, the researchers create a table of their results with categories of equal size, ranging from 0-100^o. This example shows the _______ scale of measurement.

ratio

A sample is asked to individually add up the amount of cash in their pockets, wallets, and purses. Each member’s amount is then measured in ordered, equal categories starting at $0. This example shows the _______ scale of measurement.

∑X or sum of X

adding all the X-value scores.

∑X² or the sum of X squared

squaring all the X-value scores, then adding them together.

(∑X)² or squaring the sum of X

adding all the X-value scores, then squaring the result.