A Level Biology Practice Exam 2026 – All-in-One Study Guide to Excel in Your A Levels!

Stratified sampling involves dividing a population into distinct sub-groups, known as strata, based on specific characteristics relevant to the research question. This method ensures that each subgroup is adequately represented in the overall sample, therefore reducing bias and increasing the validity and reliability of the results. For instance, if researchers were studying the dietary habits of high school students, they might stratify the population by grade level, ensuring that each grade is represented in the sample. This approach allows for more precise comparisons and insights regarding the various strata within the population, leading to conclusions that better reflect the diversity present in the entire group.