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Year 8AC9M8ST04

Planning a Fair Investigation

Plan and conduct statistical investigations involving samples of a population; use ethical and fair methods to make inferences about the population and report findings, acknowledging uncertainty.

An investigation is only as honest as its weakest step. Ethics and uncertainty are part of the method, not an afterthought.

Builds onYr 8 · Random and Non-Random Sampling

Method

Write the question so it can be answered
Name the population, the variable and the measure.
Choose a fair sampling method and say why
The method must be stated, not assumed.
Report uncertainty
A sample gives an estimate, never a fact about the whole population.
Ethics: consent, privacy, honest reporting
Do not identify individuals. Do not hide results you dislike.

Worked example

e.g. Investigate how long Year 8 students at your school spend on homework.\text{Investigate how long Year 8 students at your school spend on homework.}
  1. Write the question precisely.minutes of homework per school night, Year 8, this school\text{minutes of homework per school night, Year 8, this school}
  2. Decide the sampling method and justify it.random names from the Year 8 roll\text{random names from the Year 8 roll}
  3. Say how you will measure and record.nearest 5 minutes, anonymous form\text{nearest 5 minutes, anonymous form}
  4. Collect, then check the data before using it.look for impossible values\text{look for impossible values}
  5. Analyse, and report centre and spread.median and range\text{median and range}
  6. State the uncertainty and the limitations.one year level, one school, n=40\text{one year level, one school, } n = 40

Practice

Judge the plan, not the arithmetic.

1
Why report the range as well as the median?\text{Why report the range as well as the median?}
AnswerTwo groups can share a median and differ hugely in spread.\text{Two groups can share a median and differ hugely in spread.}
2
You sample 40 of 180 students. Can you state a fact about all 180?\text{You sample 40 of 180 students. Can you state a fact about all 180?}
AnswerNo. You can estimate, with uncertainty.\text{No. You can estimate, with uncertainty.}
3
Why keep responses anonymous?\text{Why keep responses anonymous?}
AnswerPrivacy, and people answer more honestly.\text{Privacy, and people answer more honestly.}
4
Your result disagrees with what you expected. What now?\text{Your result disagrees with what you expected. What now?}
AnswerReport it. Discarding it would be dishonest.\text{Report it. Discarding it would be dishonest.}
5
Name one thing that must appear in every report.\text{Name one thing that must appear in every report.}
AnswerHow the sample was chosen.\text{How the sample was chosen.}
6
Is a sample of your five friends acceptable?\text{Is a sample of your five friends acceptable?}
AnswerNo. It is neither random nor large enough.\text{No. It is neither random nor large enough.}
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