4 mistakes learners make with sampling and data collection, each one named and explained.
A sample tells you about the population only if the way it was chosen gave everyone a fair chance of being in it.
You ask: do you agree that too much homework is unfair?
The question reads naturally, because it is phrased the way you already think.
Question. Is this a fair survey question: do you agree that too much homework is unfair?
A common answer. yes, it offers agree or disagree
The answer. no. It suggests the answer before asking
Why. Too much and unfair are the writer's opinion, and asking do you agree invites a yes.
Read it back as if you disagreed. If that feels awkward, rewrite it.
You say a survey of the school football team represents the whole school, because they are all pupils at the school.
Everyone asked really is part of the population, so the sample looks fair by definition.
Question. A survey about sport asks the football team. Is that a fair sample of the school?
A common answer. yes, they are all pupils at the school
The answer. no. People who chose football are not like everyone else on this question
Why. Coming from the population is not enough. Everyone has to have had a fair chance of being asked.
Ask who could never have been picked. They are the ones the sample will miss.
You say data is primary because nobody else has collected it.
Primary sounds like first and therefore only, and secondary sounds like second hand.
Question. What makes data primary?
A common answer. that nobody else has collected it
The answer. that you collected it yourself for your own question
Why. Two people can collect the same measurements. It is primary for whoever gathered it.
Ask who did the collecting, not how rare the data is.
You offer 0 to 10, 10 to 20, 20 to 30, so someone who is exactly 10 can tick two boxes.
The numbers look tidy and continuous, and the join is the only place it goes wrong.
Question. Boxes read 0 to 10, 10 to 20, 20 to 30. What is wrong?
A common answer. nothing, they cover every value
The answer. someone with exactly 10 fits two boxes
Why. Every value must fit exactly one box, so write 0 to 9, 10 to 19, 20 to 29, or use a clear inequality.
Test the joins. Put each boundary number through and count the boxes it fits.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.