Inferential statistical testing

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Psychology unit 4 research methods revision
Inferential statistical testing
Used to determine if your results are significant or due to chance. Each test looks
at the sample and the size of the difference between the 2 groups to estimate if
they are different or linked. The accepted level of significance is 5% which means
95% of the time the results are significant and it is possible that the results are
due to chance and not the manipulation of the IV.
Choosing a statistical test
Spearman's rank is used if the study is investigating a correlation. If a
difference was investigated then the level of data (ordinal or nominal).
Chi squared is used if the study is looking for a difference and if the level
of data is nominal (named categories). The score of each category is
described as frequencies.
Mann Whitney U test is used if the study is looking for a difference, if the
level of data used was ordinal and if the type of experimental design used
was independent groups.
Wilcoxon T test is used if the study looks for a difference, if the level of
data is ordinal and if the type of experimental design was repeated
measures.
Spearman's rank: looks at a correlation co-efficient called Rho which is between
+1 and -1. To see if Rho is significant, a significance table is used along with the
number of participants (N) and the type of hypothesis (one or two tailed). To be
significant, Rho needs to be greater than the critical value which means that we
can then reject the null hypothesis and accept the alternate hypothesis and the
significance of the results. The + and ­ symbol in the value of Rho is ignored when
finding if Rho is significant or not (e.g. +0.58 or -0.58).
Chi squared: the calculated value of chi needs to be greater than the critical value
in order to be significant and therefore reject the null hypothesis and accept the
alternate hypothesis. Findings from an investigation involving chi squared are
presented in a contingency table. To calculate the degree of freedom the number
of rows (minus 1) is multiplied by the number of columns (minus 1). This is used to
find the critical value by referring to a critical value table to see if the critical
value is greater than the chi value. If it is then there is a significant difference
between the 2 groups.
Mann Whitney U test: a value for this is calculated. The sample sizes of the 2
groups are needed along with the type of hypothesis to look up the critical value
to see if there is a significant difference. In order to be significant, the value of
U must be lower than the critical value.

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Psychology unit 4 research methods revision
Wilcoxon T test: the value of T is calculated. The sample size (N) is needed along
with the type of hypothesis. To be significant the value of T needs to be the same
or lower than the critical value.…read more

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