What you’ll learn
Judge whether samples represent populations.
Key idea
A proportionally stratified design matches a measured population feature; it still needs an appropriate chance mechanism inside each grade.
Matching one demographic proportion does not prove unbiasedness for every trait; preserve subgroup eligibility and within-stratum selection.
Worked example
Enter the exact value or ordered values in the format requested below.
A school is 20% Grade7 and 80% Grade8. Plan 60 sampled pupils matching this grade mix, chosen randomly within each grade. Enter required Grade7 count.
- Grade7 is 20% and Grade8 is 80% of this school.
- A matching 60-pupil mix is 12 Grade7 and 48 Grade8; random selection within each grade addresses selection bias, while matching grade mix alone does not prove representation on every trait.
Answer: 12
Quick Check
Interpret the result of 'Judge whether samples represent populations' in the data-generating context, including units and population limits.
Population grade mix is 50% Grade7 and 50% Grade8. For 10 pupils compare A:(5,5), B:(6,4), C:(4,6), in Grade7,Grade8 order. Interpret which matches this demographic feature, without assuming all traits are represented.