Planning & Data Collection

This unit covers the statistical enquiry cycle, writing hypotheses, types of data, populations and samples, sampling methods, questionnaire design, controlling variables, cleaning data and the capture-recapture method at Higher tier.

It is the least mathematical unit on the course and the most frequently underestimated. Marks come from precision of language: qualitative and quantitative, discrete and continuous, primary and secondary are all used exactly in mark schemes. Sampling methods need learning with an advantage and a disadvantage each, and questions usually ask you to justify a choice for a specific situation rather than to define a term. Bias is the concept students handle least well — a larger sample reduces random variation but does not remove bias, and stating that clearly earns marks that vague answers about fairness do not.