Types of Data and Sampling

Categorical vs. Quantitative Data

Data can be classified into two main types:

Categorical (Qualitative) Data describes qualities or characteristics. Examples include eye color, zip code, or political party. Categorical data can be:

• Nominal: No natural ordering (e.g., blood type: A, B, AB, O)
• Ordinal: Has a natural order (e.g., satisfaction: low, medium, high)

Quantitative (Numerical) Data represents measurable quantities. It can be:

• Discrete: Countable values (e.g., number of siblings: 0, 1, 2, 3…)
• Continuous: Any value in a range (e.g., height: 5.7 ft, weight: 150.3 lbs)

Individuals and Variables

• Individuals are the objects described by a set of data (people, animals, things)
• Variables are characteristics of an individual

Levels of Measurement

| Level | Description | Example | |-------|-------------|---------| | Nominal | Categories with no order | Gender, color | | Ordinal | Categories with order | Grade level, ranking | | Interval | Ordered, equal spacing, no true zero | Temperature (°F) | | Ratio | Ordered, equal spacing, true zero | Weight, height |

Key Vocabulary

• Population: The entire group of interest
• Sample: A subset of the population used to draw conclusions
• Parameter: A number that describes the population (usually unknown)
• Statistic: A number computed from a sample (used to estimate a parameter)

AP Tip: The AP exam frequently tests your ability to classify data types and identify appropriate displays for each type.