Data Types, Planning and Primary/Secondary Sources

Start with good data 📊

Before you can draw a chart or work out an average, you must **collect data well**. Choosing the right type, source and plan is what makes a statistical enquiry trustworthy. This module covers the types of data, where it comes from, and how to plan an investigation.

Qualitative and quantitative 🔢

The first split is whether the data is in **words** or **numbers**: - **Qualitative** data describes qualities in words (eye colour, favourite sport). - **Quantitative** data is **numerical** (height, number of pets).

What type is it?

A survey records each person's eye colour. What type of data is this?

• Qualitative
• Quantitative
• Discrete
• Continuous

Discrete and continuous 📏

Quantitative data splits again: - **Discrete** data can only take **separate, countable** values (number of goals, shoe count). - **Continuous** data is **measured** and can take any value in a range (height, time, mass).

Match each example to its data type

Which is continuous?

Select the THREE examples of continuous data.

• The height of each student
• The time taken to run 100 m
• The mass of each parcel
• The number of goals scored
• The number of pets owned
• Favourite colour

Primary and secondary sources 📚

Data also differs by **who collected it**: - **Primary** data is collected by **you**, for **your** purpose (a survey or experiment you run). - **Secondary** data was collected by **someone else** (a census, published statistics, a website). It must be **acknowledged**, and you should check its reliability and accuracy.

Primary or secondary?

For your project you use figures from a published government census. What kind of data is this?

• Secondary data
• Primary data
• Continuous data
• Qualitative data

Reliability and validity 🎯

Two words examiners define precisely: - **Reliability** is the extent to which **repeated measurements yield similar results**. - **Validity** is the extent to which a test **measures what was intended**. A bathroom scale that always reads 2 kg heavy is reliable (consistent) but not valid (wrong value).

Match each term to its meaning

Planning an enquiry 📝

A statistical enquiry starts with a **hypothesis**: a testable statement you set out to investigate. You then plan how to collect the right data to test it. Good planning weighs up **constraints**: time, cost, ethical issues, confidentiality and convenience.

What is a hypothesis?

In a statistical enquiry, what is a hypothesis?

• A testable statement or prediction the investigation sets out to test
• The final conclusion after collecting data
• A type of graph
• The average of the data

Plan an investigation

An interactive activity.

Data collection summary

Numerical data is _____, while descriptive data is qualitative. Data you collect yourself is _____, while data from someone else is secondary. _____ is the extent to which repeated measurements agree. A testable prediction is called a _____.