Authoring a PhD Thesis How to Plan, Draft, Write and Finish a Doctoral Dissertation by Patrick Dunleavy

180 ◆AUTHORING A PHD

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45

40

Customer satisfaction (%)

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30

25

20

15

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02 46

Flights delayed (%)

8101214

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(h) Scatterplot or ‘X and Y’ graph

The relationship between flight delays and customer
satisfaction levels, airports in USA 2000 (hypothetical)

Use an ‘X and Y’ chart or scatterplot whenever:

• you want to show how the level of a dependent
  variable (shown on the vertical Y axis) varies
  depending on the level of an independent variable
  (shown on the horizontal X axis).

Don’t use an ‘X and Y’ chart if:

• the two variables are not meaningfully associated or
  you are not positing a causal link from the X variable
  to the Y variable.

Points to watch:

• make sure that the variables are the right way round: the
  dependent (influenced) variable must always be on
  the Y axis, and the causing or influencing variable on
  the X axis, or otherwise readers will be deeply confused;


• adding a regression line (or line of ‘best fit’) will help
  readers see the nature of the association more clearly.
  This line is the one which minimizes the vertical
  distances from the line of the data points above and
  below the line.