Published 3 September 2008, doi:10.1136/bmj.a196
Cite this as: BMJ 2008;337:a196

Endgames

Statistical question

Continuous variables

John Fletcher, clinical epidemiologist

1 BMJ, London WC1H 9JR

jfletcher@bmj.com

The first 150 words of the full text of this article appear below.

How would you best begin to explore the distribution of a continuous variable?

a) Scatter plot
b) Box plot
c) Histogram
d) Hypothesis test

c—A histogram displays the frequency of all the data divided into suitable intervals.

A histogram is perhaps the most commonly used graphical method of displaying either continuous data, such as height, or discreet data, such as mortality. The horizontal axis displays the limits that are used for each interval. For each interval a rectangular column centred on the midpoint is drawn rising from the horizontal axis. The vertical axis measures the number of values that fall within each interval or, if desired, the percentage of values that fall within each interval.

Scatter plots usually display the relation between two continuous variables plotted on the x and y axes. A one way scatter plot may be used to display a single continuous variable, but a disadvantage . . . [Full text of this article]


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