advanced applied science: GCE A2 UNITS
© The Nuffield Foundation 2008
FACT SHEET
Choosing a statistical test
Introduction
From Fact sheet: Background to statistics:
‘Statistics’ include a broad range of methods for manipulating, presenting and interpreting
data. Professional scientists of all kinds need to be proficient in the use of statistics: they
must be able to recognise and communicate what their data show.
The fact sheet summarises the usefulness of statistics. If you do not have a copy, ask your
teacher for one.
Scientists have a number of statistical tests to choose from. Use the table on the next page
to choose a test appropriate to your data investigation. Then, where possible, use Excel to
help you to make the calculations.
How to use the table

Start on the left and work your way across the table until you find Test to choose.

Look in the Excel column to see if there is a statistical function that you can use.

Look in the p < 0.05 column to see what a probability of less than 1 in 20 means for
your conclusions.
Choosing a statistical test: page 1 of 2
advanced applied science: GCE A2 UNITS
© The Nuffield Foundation 2008
Type of data
Frequencies
(counts of
categories)
Type of test
Test to choose
Compares observed and expected values
Large samples
(>30)
Differences
between
means of
normal data
(parametric)
Measurements
(continuous
interval scale)
2 sets of data
Small (>5)
or large
samples
2
Standard error of the
difference
ANOVA
Differences between medians of non-normal
data (non-parametric)
Testing for a relationship
Finding how
factors are
related
Choosing a statistical test: page 2 of 2
p < 0.05
Hypothesis
predicts
numbers
=CHITEST()
Difference
between
counts
Association
No Excel function but can be
calculated*
reject hypothesis
significant difference
significant association
significant difference
*=SQRT((VAR(range 1)/COUNT(range 1))+VAR((range 2)/COUNT(range 2))
Paired data
significant difference
(type1)
t-test
=TTEST()
Unpaired data significant difference
(type2)
More than
2 sets of data
Testing for
correlation
Excel
Tools>Data
analysis>Anova
significant difference
Mann-Whitney U-test
No Excel function
significant difference
Pearson’s correlation
coefficient
=PEARSON()
Tests for zero
correlation
significant correlation
Spearman’s correlation
coefficient
Use =PEARSON()
on ranked data
Tests for zero
correlation
significant correlation
Linear regression
Use trendline and
Gives slope
and intercept
(not a probability test)
display equation