3.2 Sampling & Data Collection

Population vs. sample

The population is everyone your question concerns; a sample is the subset you actually study. A representative sample lets you generalize more confidently.

Sampling methods

Random sampling gives everyone an equal chance and reduces bias; convenience sampling (whoever's available) is easier but can skew results. Note your sampling's limits.

Collecting data

Design instruments carefully: clear, unbiased survey questions; consistent interview protocols; systematic observation. Avoid leading questions that push a particular answer.

Key terms

Population

everyone your question concerns

Sample

the subset you actually study

Random sampling

equal chance for all — reduces bias

Convenience sampling

whoever's available — can skew results

Leading question

pushes a particular answer — avoid it

Try an AP-style question

A random sample helps…

1. guarantee a large and clear effect
2. avoid the need for informed consent
3. shorten the length of the study
4. reduce bias and represent the population