# S1 Statistics Revision - Chapter 4 Notes

Chapter 4 - Methods of summarising data (dispersion)

- Created by: Megan Wilkinson
- Created on: 17-05-12 17:59

First 195 words of the document:

AS Statistics Revision

Statistics 1 Chapter 4

Methods of summarising data (dispersion)

Key points to remember

Range = the value obtained when the smallest observation in

a

data set is subtracted from the largest one.

Interquartile range (IQR) = the value obtained when the

lower

quartile is subtracted from the upper quartile.

IQR = Q3 Q1

Outlier = an extreme value which does not fit into the main

body

of the data. Any rules to identify outliers will be specified in

the

S1 question paper. The usual equation tends to be either

For the lower outlier limit = LQ (1.5 x IQR)

For the upper outlier limit = UQ + (1.5 x IQR)

Variance = the variance of a population of observations. This

is

the standard deviation squared.

i.e. (fx² ÷ n) x²

Standard deviation = (fx² ÷ n) x²

Skewness = an indicator of the shape of a distribution.

Symmetrical: mode = median = mean

Positive Skew: mode < median < mean

or Q2 Q1 < Q3 Q2

Negative Skew: mean < median < mode

or Q2 Q1 > Q3 Q2

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