Glossary
Categorical Variables
Variables that place individuals into categories or groups based on attributes or labels.
Example:
A survey asking about a person's 'preferred mode of transportation' (e.g., car, bus, bike) collects categorical variables.
Continuous Variable
A type of quantitative variable that can take any value within a given range.
Example:
A person's 'height' is a continuous variable because it can be 170 cm, 170.5 cm, 170.53 cm, and so on, within a range.
Data
The values that variables take on for each individual.
Example:
If we record the heights of 20 students, the list of 20 height measurements constitutes the data.
Discrete Variable
A type of quantitative variable that can only take on a finite number of values or a countably infinite number of values, often whole numbers.
Example:
The 'number of pets' a household owns is a discrete variable because you can have 0, 1, 2 pets, but not 1.5 pets.
Distribution
The pattern of variation of a variable, showing what values the variable takes and how often it takes them.
Example:
A histogram showing the frequency of different exam scores illustrates the distribution of scores.
Individuals
The objects or people described by a set of data.
Example:
In a study about student performance, each student surveyed is an individual.
Interval
A level of measurement for quantitative data where differences between values are meaningful, but there is no true zero point, meaning zero does not indicate the absence of the quantity.
Example:
Temperature measured in Celsius or Fahrenheit is an interval variable; 0°C doesn't mean no temperature, and 20°C is not 'twice as hot' as 10°C in terms of absolute energy.
Nominal
A level of measurement for categorical data where categories have no inherent order or ranking.
Example:
Classifying students by their 'favorite color' (e.g., blue, red, green) is at the nominal level because there's no natural order.
Ordinal
A level of measurement for categorical data where categories have a meaningful order or ranking, but the differences between categories are not quantifiable.
Example:
Rating a movie on a scale of 'Poor, Fair, Good, Excellent' is an ordinal variable because there's an order, but the 'distance' between Poor and Fair isn't necessarily the same as between Good and Excellent.
Quantitative Variables
Variables that represent numerical values that can be measured or counted.
Example:
The 'number of text messages sent per day' is a quantitative variable because it's a numerical count.
Ratio
A level of measurement for quantitative data where differences are meaningful, and there is a true zero point, indicating the complete absence of the quantity.
Example:
A student's 'score on a test' (e.g., 0 to 100) is a ratio variable because a score of 0 means no correct answers, and a score of 80 is twice as many correct answers as 40.
Variable
A characteristic that can vary from one individual to another.
Example:
When studying a class, 'favorite subject' is a variable because it differs among students.