Data collection

A useful conclusion starts with a clear question and a sound way to collect evidence.

Work through twelve lessons on populations, sampling methods, data types and weather records. Finish with an original spreadsheet investigation and mixed practice.

Populations, samples and censusesDefine the population you want to study, distinguish a sample from a census, and see why sample estimates vary. Original examples, a manual model and worked practice.
Sampling frames and biasCheck who a sampling frame includes, spot coverage and response problems, and explain why a larger sample does not automatically remove bias. Original scenarios and worked practice.
Simple random samplingSelect a fixed number of distinct units fairly, handle repeated random labels, and understand what makes a sample simple random. Original examples and worked practice.
Systematic samplingCalculate a sampling interval, choose a random start and select a fixed-size sample. Explore how repeating patterns in a list affect systematic samples.
Stratified samplingDivide a population into non-overlapping strata, allocate a proportional sample, handle rounding and select randomly within each group. Original examples and worked practice.
Quota and opportunity samplingDistinguish opportunity, quota and stratified random sampling. Explain practical advantages, identify selection bias and improve survey plans with original worked examples.
Types of dataDistinguish qualitative and quantitative variables, discrete and continuous measurements, and the underlying quantity from its rounded record. Original examples and worked practice.
Class boundaries and midpointsRead grouped classes correctly, account for recording precision, and calculate widths and midpoints. Original examples, a manual interval model and worked practice.
Large data set: weather contextUnderstand the places, dates and limits of the Pearson Edexcel weather large data set. Choose a meaningful population and interpret seasonal comparisons.
Trace, missing data and weather samplesDistinguish trace rainfall, measured zero and missing data. Compare cleaning decisions with an original synthetic table and explain their effects on means and sample size.
Plan a data collection investigationPlan a sampling investigation, calculate estimates from an original small dataset and judge the design. Includes a learner-operated comparison and downloadable spreadsheet.
Data collection: mixed practiceOriginal cumulative questions on sampling designs, bias, data types, grouped measurements and weather records, with separate hints and worked solutions.