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Principles of Research and Application of Research Methods

Descriptive Statistics: the range, the standard deviation and choosing a measure

  • 3 things to know
  • AS Unit 2

Overview

When the mode is the only measure available, the range and the standard deviation calculated and compared, and choosing a measure to suit the level of measurement.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Numbers

When is the mode the only measure available, what is the mode of 2, 3, 3, 5, 7, 7, 7 and 9, and what problem can the mode have?

Key term

What does a measure of dispersion tell you?

Key term

Give one problem with using the mode.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    When is the mode the only measure of central tendency available?

    Model answer

    When the data are nominal, because categories can be counted but not ordered or averaged.

  2. 2

    Give one problem with using the mode.

    Model answer

    A set of data may have two modes or none at all, and the mode can shift a long way when only a few scores change.

  3. 3

    What does a measure of dispersion tell you?

    Model answer

    How spread out the scores are around the central value, and therefore how varied or consistent the participants were.

  4. 4

    How is the range calculated?

    Model answer

    By subtracting the lowest score in the set from the highest.

  5. 5

    The fastest participant completed a task in 12 s and the slowest took 47 s. State the range.

    Model answer

    The range is 35 s.

  6. 6

    Why is the range a crude measure of dispersion?

    Model answer

    It uses only the two most extreme scores, so a single unusual participant can make a tightly clustered set of data look widely spread.

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