Types of Data

Data is information we collect to answer a question. There are two main types: categorical and numerical.

Categorical Data

Data that falls into categories or groups. It describes qualities, not quantities.

Favourite sport (cricket, netball, soccer)
Eye colour (brown, blue, green)
Transport type (bus, car, walk)

Numerical Data

Data that is counted or measured. It can be discrete or continuous.

Discrete: number of siblings (0, 1, 2, 3...)
Continuous: height in cm (167.3 cm)
Continuous: time in seconds

Tip: Discrete data is counted (whole numbers only). Continuous data is measured and can take any value within a range.

Designing Surveys

A survey is a set of questions used to collect data from people. Good survey questions are clear, unbiased, and easy to answer.

Poor Survey Question

"Don't you think our school canteen sells unhealthy food?"

Problem: biased — it leads the respondent to a particular answer.

Good Survey Question

"How would you rate the healthiness of the school canteen food?"

This is neutral and gives the respondent a fair choice.

Tips for Good Survey Design

✓ Use clear and simple language
✓ Ask one thing at a time
✓ Avoid leading or biased wording
✓ Provide suitable response options

Sampling Methods

A population is the entire group we want to study. Because it is often too large to survey everyone, we take a sample — a smaller group chosen to represent the whole.

Random Sampling

Every person in the population has an equal chance of being selected. Example: names drawn from a hat. Least biased method.

Stratified Sampling

The population is divided into groups (strata) and a sample is taken from each. Example: surveying equal numbers of boys and girls.

Convenience Sampling

Surveying whoever is easiest to reach. Example: asking only your friends. This can introduce bias.

Frequency Tables

A frequency table organises data by listing each category or value alongside the number of times it occurs (its frequency). Tally marks help count raw data.

Favourite Sport	Tally	Frequency
Cricket	\|\|\|\| \|	6
Netball	\|\|\|\|	4
Soccer	\|\|\|\| \|\|\|	8
Basketball	\|\|	2
Total		20

Key Vocabulary

Population

The entire group a researcher wants to gather information about.

Sample

A smaller group selected from the population to represent it in a study.

Frequency

The number of times a particular value or category appears in a data set.

Bias

A tendency to favour certain outcomes, making the data unfair or unrepresentative.

Worked Examples

1

Classify each as categorical or numerical: (a) number of books read, (b) hair colour, (c) temperature in Celsius.

(a) Number of books read — Numerical (discrete)

(b) Hair colour — Categorical

(c) Temperature in Celsius — Numerical (continuous)

2

The following scores were recorded: 3, 5, 3, 4, 5, 3, 4, 5, 5, 3. Complete a frequency table.

Score	Frequency
3	4
4	2
5	4

3

Identify the sampling method: A teacher randomly selects 5 students from each of 4 classes to survey about homework habits.

The population is divided into groups (classes) and samples are taken from each group. This is stratified sampling.

Knowledge Check

Select the correct answer for each question.

Question 1

Which of the following is an example of categorical data?

Number of goals scored Weight in kilograms Temperature in degrees Favourite subject at school

Question 2

The number of pets owned by students (0, 1, 2, 3...) is an example of which type of numerical data?

Discrete Continuous Categorical Biased

Question 3

A student surveys only their friends about their favourite food. What type of sampling is this?

Random sampling Convenience sampling Stratified sampling Population survey

Question 4

In a frequency table, the data values 3, 3, 4, 5, 3, 4 are recorded. What is the frequency of the value 3?

2 4 3 6

Question 5

Which survey question is the most unbiased?

"Don't you think we need more sport at school?" "Sport is boring, isn't it?" "Everyone agrees sport is great — how often do you play?" "How many hours of sport per week do you prefer?"

Data Collection