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Principles of Research and Application of Research Methods

Levels of Measurement: interval data and ratio data

  • 3 things to know
  • AS Unit 2

Overview

Recall questions on interval data and ratio data.

What you need to know

Answer each one before you reveal it.

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Key term

Why is it a mistake to calculate a mean from ordinal data?

Key term

Define ratio data.

Key term

What property does interval data have that ordinal data lacks?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What property does interval data have that ordinal data lacks?

    Model answer

    Interval data are measured on a scale with equal, fixed intervals, so the difference between any two adjacent points is the same size.

  2. 2

    State one example of interval data used in psychology.

    Model answer

    A score on a standardised intelligence test.

  3. 3

    Why is an interval scale said to have no true zero?

    Model answer

    Its zero point is arbitrary rather than meaning a complete absence of the quality being measured, so a score of zero does not mean the person has none of it.

  4. 4

    Define ratio data.

    Model answer

    Ratio data are measured on a scale with equal intervals and a true zero point, so zero means that none of the quantity is present.

  5. 5

    Give two examples of ratio data from psychological research.

    Model answer

    Reaction time in seconds and the number of words recalled from a list.

  6. 6

    Why can you say a reaction time of 0.8 s is twice as long as one of 0.4 s, but not that a test score of 140 shows twice the intelligence of a score of 70?

    Model answer

    Reaction time is ratio data with a true zero, so ratios are meaningful, whereas the test score is interval data with an arbitrary zero and cannot be compared as a multiple.

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Psychology Past to Present — The Five Approaches
Contemporary Debates
Principles of Research and Application of Research Methods
Mathematical Requirements for Psychology (Appendix A: AS Unit 2 and A2 Unit 4)

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