Making and justifying an inference

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Worksheet with answersDownload PDF

What this lesson covers

  • Answer the question in its own words.
  • Use the interval, with units.
  • Discuss the sampling and sources of error.
Key idea

The structure

  • Say what you estimate or claim, about which population.
  • Give the interval with units.
  • Explain the evidence from the graphs.
  • Discuss how the sample was taken and what could affect it.
Worked example

A model answer

  • Sample of 36 students, median 52 minutes, interval 47.5 to 56.5.
PartSentence
ClaimI estimate the median travel time for Year 12 students at this school is between 47.5 and 56.5 minutes.
EvidenceThe sample median is 52 minutes and the middle half of times span 18 minutes.
TrustThe sample was random, so it should represent the year, though 36 students gives a fairly wide interval.

Common mistakes

  • Writing about the sample median as the answer.
    State the likely range for the population.
  • Saying the sample was big enough with no reason.
    Link sample size to the width of the interval.

Your turn

  • 1. What are the four parts of a strong conclusion?
  • 2. How could you make the interval narrower?
Show answer

1. Claim, interval, evidence, and comments on the sampling 2. Take a larger sample

Summary

What to take away

  • Claim, interval, evidence, trust.
  • Always write about the population.

More in AS 91264

Sampling and the enquiry cycleNotesBox plots and informal confidence intervalsNotesComparing two samplesNotesMaking and justifying an inferenceNotes

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