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Collecting data: samples, questionnaires and class intervals

Population and sample, good questionnaires, class intervals and stem-and-leaf displays. Read one part at a time and tap “I know this”. Then test yourself in the quiz.

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Collecting data

  • A population is the whole group; a sample is a smaller group that represents the whole.
  • A good questionnaire has clear, fair questions without bias.
  • Group large data sets in class intervals: 0–9, 10–19, 20–29.
  • Sources of data: classmates, family, newspapers, books and the internet.
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Questionnaires

  • Yes/no questions: “Do you have a pet?” Yes / No.
  • Multiple-choice questions: “How do you get to school? A. walk B. bus C. car D. bicycle”.
  • Avoid a leading question such as “Don’t you agree that soccer is the best sport?”: it pushes people towards one answer.
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Tally marks, frequency tables and stem-and-leaf

Organise data with tally marks and a frequency table (how many times each value or interval occurs).

In a stem-and-leaf display the stem is the tens digit and the leaf is the units digit; write the leaves in order. Data 23, 25, 31, 36, 36, 42:

StemLeaves
23 5
31 6 6
42

Key: 2 | 3 = 23.

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Remember this and test yourself

Remember this: your summary
  • Sample = smaller group from the population.
  • Questionnaire questions must be clear and fair: yes/no or multiple choice.
  • Class intervals group data.
  • Stem-and-leaf: stem = tens, leaf = units.
  • Avoid leading questions.

Write these points in your book. Read them again the night before the test.

Memory trick

Taste the pot of soup with one spoon: that is a sample.

Flash cards · Tap to turn over

Important words

First say the answer yourself, then turn the card over.

Test yourself · Part 2

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