Maths: Collecting Data (GCSE, Edexcel)

Primary Data

Primary Data

Information you yourself collect, by asking people, measuring, or carrying out experiments.

Secondary Data

Information that has been collected already, such as from books or the internet.

Qualitative Data

Data that is descriptive and opinion-based and thus cannot be quantified.

Quantitative Data

Data that can be quantified and shown in a diagram such as measurements and figures.

Discrete Data

Numerical data that can’t be shown in decimals.

Continuous Data

Numerical data that can be shown in decimals.

Sample

Part of the data

Population

All of the data

Data collection cycle

• Specify the problem

• Collect data

• Process and represent data

• Interpret data

Appropriation formula

(data point / sample size) x population size

The assumption made when appropriating

The sample is representative of the population.

Random sampling

When each piece of data has an equal chance of being selected.

Random sampling methods

• Assign every piece of data a number. Pick the numbers at random (e.g. out of a hat)

• Assign every piece of data a number. Use the random number generator on your calculator to pick a number at random.

Stratified sampling

Dividing the population into groups (stratas) so that when a sample is taken, the number of data points taken from each group is proportional to their strata size.

Strata sample size formula

(size of strata / total population) x total sample size

Capture-recapture strategy

The fraction of (tagged on recapture / total recapture amount) is equivalent to (original tagged amount / total population)

Assumptions made when using capture-recapture

• The population did not change between capture and recapture

• No marks/tags were removed

• The marked group mixed thoroughly with the population