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Choosing a statistical test
If the study was investigating a correlation then the spearman's rank test
should be used. If the study was investigating a significance difference
between two groups then the level of data used in the investigation must be
If the data used in the investigation was nominal then Chi squared must be
used. Nominal data is data grouped into categories. The scores of each
category are described as frequencies.
The other type of data that could be used is ordinal which is data in the
form of ratings and rankings and anything that can be put in a position. As
spearman's rank requires the data to be ranked that too is also ordinal data.
Any investigation using ordinal data will either use a Wilcoxon T test or a
Mann Whitney U test as they both are used for ordinal data. To decide
which test to use for ordinal data the experimental design used in the
investigation must be considered. If a repeated measures design is used
then the Wilcoxon T test is used and if an independent groups design is used
then the Mann Whitney U test is used.
The correlation co-efficient which is called Rho; this is between +1 and -1. To see
if it is significant, a significance table is used along with two other pieces of
information which are the number of participants (N) and the type of hypothesis
(one or two tailed). To be significant, Rho needs to be the same or greater than
the critical value. In order to find the critical value the Rho, number of
participants and the type of hypothesis is needed. The + or symbol in the value
of Rho (e.g. +0.58 or -0.58) is ignored when finding if Rho is significant.
Chi squared test
Used when the data is nominal and when we are looking for a difference between
two groups. The calculated value of chi squared needs to be compared to the
critical value. If chi is greater than the critical value or the same as the critical
value then we reject the null hypothesis and say there is a significant difference.
Findings from an investigation involving chi squared as a statistical test are
presented in a contingency table. To calculate the degree of freedom the number
of rows minus one is multiplied by the number of columns minus one. This is then
used to find out the critical value by referring
to a critical value table and then if the critical
value is the same as or greater than the chi
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value then there is a significant difference between the two groups tested.
Mann Whitney U test
Used in an experiment as we are looking for differences between two variables
and is used with ordinal data, when an independent sample design is used. A value
for U is calculated.…read more