Measurement Concepts & Variable Types
The variable manipulated or controlled in a study.
Independent Variable
Categories with no order (e.g., types of fruit).
Nominal Measurement
Numbers that describe the basic features of data.
Descriptive Statistics
The spread of values in a dataset.
Dispersion
Shows how often each value occurs in a dataset.
Frequency Distribution
The outcome measured based on changes to the independent variable.
Dependent Variable
Categories with a ranked order (e.g., 1st, 2nd, 3rd).
Ordinal Measurement
Describes the center or average of a dataset.
Central Tendency
Difference between the highest and lowest values.
Range
A measure of asymmetry in a distribution.
Skew
Variables with distinct groups or categories (e.g., gender, color).
Categorical Variables
Ordered with equal intervals, but no true zero (e.g., temperature in °C).
Interval Measurement
The arithmetic average
Mean
Average of the squared differences from the mean.
Variance
A measure of whether data are heavy-tailed or light-tailed.
Kurtosis
Variables with numeric values along a scale (e.g., height, income).
Continuous Variables
Ordered, equal intervals, with a meaningful zero (e.g., weight, age).
Ratio Measurement
The middle value when data is ordered
Median
A measure of how much values deviate from the mean.
Standard Deviation
A bell-shaped, symmetrical distribution of data.
Normal Distribution
Describes how data is categorized or measured.
Measurement Level
The most frequent value in a dataset.
Mode
The total of each data point’s squared difference from the mean.
Sum of Squares