Which type of inferential test should be used?

What is the criteria that it depends on? whether the researcher is testing for differences between groups (experiment) or a correlation between two co- variables. Level of measurement (nominal, ordinal interval) Experimental design (independent groups, matched pairs, repeated measures)

Can you remember the 7 statistical tests? The seven tests that you can be asked about (but won’t have to calculate) in the exam: Chi-squared (χ2) Wilcoxon T Mann-Whitney U Spearman’s Rho Unrelated t-test Related t-test Pearson’s r How do you know which test to use? You need to learn the following criteria, but there is no need for you to understand why this is the case

LOOKING FOR A CORRELATION REPEATED MEASURES DESIGN What test to use? Looking for a difference LOOKING FOR A CORRELATION DATA LEVEL INDEPENDENT GROUPS DESIGN REPEATED MEASURES DESIGN   NOMINAL Chi-square Sign Test Chi square ORDINAL Mann-Whitney U test Wilcoxon test Spearman’s rho INTERVAL OR RATIO Unrelated t test Related t test Pearsons r

Test of difference or correlation At Interval level At Interval level Nominal or at least ordinal level data? At ordinal level Pearson’s r Repeated measures Independent groups design Spearman’s Rho Related t test Chi square Chi can also be association. Correlation between chewing gum and having nice breadth. independent groups design? Repeated measures/matched pairs or independent groups design? Mann-Whitney U Test Wilcoxon T Related t test

Chi-Squared Chi-Squared = nominal data = independent groups design

Independent groups Design Mann-Whitney U Test- Independent women Rank first in the charts Independent groups Design Ordinal data

Wilcoxon T Test Wilcoxon T Test Repeated measures- At least ordinal (1st in the race) Cok sits at the front. Repeating movement. Want to come first.

Spearmans Rho There is a correlation between spearmints chewing gum and fresh breath

Unrelated t-test When you are single, you are independent and Unrelated to a partner, so you have an interval from household chores

Related t-test Back with your partner…. The interval is over… Being related to someone else means…. Repeatedly having to do the household chores

Pearson’s r Brighton Pear is correlational to the west pier. The interval between is made up of a pebbly beach and too many tourists in the summer.

Test of difference or correlation At Interval level At Interval level Nominal or at least ordinal level data? At ordinal level Pearson’s r Repeated measures Independent groups design Spearman’s Rho Related t test Chi square Chi can also be association. Correlation between chewing gum and having nice breadth. independent groups design? Repeated measures/matched pairs or independent groups design? Mann-Whitney U Test Wilcoxon T Related t test

Which test to choose. Activity Have a go at trying to draw the diagram yourself on mini whiteboard.

See handout… What test to use? Looking for a difference Looking for a correlation Independent groups design   Nominal Not possible Interval or Ratio Unrelated t test Pearsons r

LOOKING FOR A CORRELATION REPEATED MEASURES DESIGN What test to use? Looking for a difference LOOKING FOR A CORRELATION DATA LEVEL INDEPENDENT GROUPS DESIGN REPEATED MEASURES DESIGN   NOMINAL Chi-square Sign Test Chi square ORDINAL Mann-Whitney U test Wilcoxon test Spearman’s rho INTERVAL OR RATIO Unrelated t test Related t test Pearsons r

Now you need to justify each test Fill in the gaps The Spearman’s Rho was used because the data can be treated as at least 1)_______________ and the researchers were studying a possible 2)_________________ between two co-variables 1 = Ordinal 2 = Correlation (or relationship)

Now you need to justify each test Fill in the gaps The Chi-Square test was used because the data can be treated as 1)_______________ and the researches had hypothesised that there will be 2)___________________ between conditions when using the 3) _________________________ design. 1 = Nominal 2 = a difference 3 = Independent groups (please note that the Chi-square is also used as a test of association)

Now you need to justify each test Fill in the gaps The Wilcoxon T test was used because the data can be treated as 1)_______________ and the researches had hypothesised that there will be 2)___________________ between conditions when using the 3) _________________________ design. 1 = ordinal 2 = a difference 3 = Repeated Measures (please note that the Wilcoxon T is also used for a matched-pairs design)

Now you need to justify each test Fill in the gaps The Mann-Whitney U test was used because the data can be treated as 1)_______________ and the researches had hypothesised that there will be 2)___________________ between conditions when using the 3) _________________________ design. 1 = ordinal 2 = a difference 3 = independent groups

Test your understanding! Using your newly found knowledge identify the test that would be suitable for the following: An experiment with nominal data and an independent groups design Ordinal data on both measures in a study to see if two measures are associated An experiment with and independent groups design in which the DV is measured on a ordinal scale A study using a correlational technique in which one measure is interval and the other is ratio. An experiment in which all participants were tested with alcohol and without alcohol on a memory test An experiment in which reaction time was tested using an independent subject design

ANSWERS An experiment with nominal data and an independent groups design chi-squared test Ordinal data on both measures in a study to see if two measures are associated Spearman’s rank correlation / Rho An experiment with and independent groups design in which the DV is measured on a Ordinal scale Mann-Whitney U test A study using a correlation technique in which one measure is interval and the other is ratio Pearsons r An experiment in which all participants were tested with alcohol and without alcohol on a memory test Wilcoxon’s T test An experiment in which reaction time was tested using an independent subject design Unrelated T-Test

Which test to choose. Activity Complete the exam questions on your hand out.