An introduction to statistics

An introduction to everyday statistics—2

P Driscoll, F Lecky, M Crosby

Accident and Emergency Department, Hope Hospital, Salford M6 8HD

Correspondence to:
Correspondence to: Mr Driscoll, Consultant in A&E Medicine (pdriscoll@hope.srht.nwest.nhs.uk)

• Describe central tendency and variability
  
• Summarising datasets containing two variables
  

In covering these objectives we will deal with the following terms:

• Mean, median and mode
  
• Percentiles
  
• Interquartile range
  
• Standard deviation
  
• Standard error of the mean
  

In the first article of this series, we discussed graphical and tabular summaries of single datasets. This is a useful end point in its own right but often in clinical practice we also wish to compare datasets. Carrying this out by simply visually identifying the differences between two graphs or data columns lacks precision. Often therefore the central tendency and variability is also calculated so that more accurate comparisons can be made.

It is usually possible to add to the tabular or graphical summary, additional information showing where most of the values are and their spread. The former is known as the central tendency and the latter the variability of the distribution. Generally these summary . . . [Full text of this article]

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