Which type of inferential test should be used

Which type of inferential test should be used?

What is the criteria that it depends on? 1. whether the researcher is testing for differences between groups (experiment) or a correlation between two covariables. 2. Level of measurement (nominal, ordinal interval) 3. 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

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

Test of difference or correlation At Interval level Nominal or at least ordinal level data? At ordinal level Repeated measures Independent groups design Spearman’s Rho Related t test Chi square independent groups design? Related t test Repeated measures/matched pairs or independent groups design? Wilcoxon T Mann-Whitney U Test Pearson’s r

Chi-Squared = nominal data = independent groups design

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

Wilcoxon T Test Repeated measures. At least ordinal (1 st in the race)

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 Nominal or at least ordinal level data? At ordinal level Repeated measures Independent groups design Spearman’s Rho Related t test Chi square independent groups design? Related t test Repeated measures/matched pairs or independent groups design? Wilcoxon T Mann-Whitney U Test Pearson’s r

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 Independent groups design Looking for a correlation Not possible Nominal Unrelated t test Interval or Ratio Pearsons r

What test to use? Looking for a difference DATA LEVEL INDEPENDENT GROUPS DESIGN REPEATED MEASURES DESIGN NOMINAL Chi-square Sign Test ORDINAL Mann-Whitney U test INTERVAL OR RATIO Unrelated t test LOOKING FOR A CORRELATION Chi square Wilcoxon test Spearman’s rho 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: 1. An experiment with nominal data and an independent groups design 2. Ordinal data on both measures in a study to see if two measures are associated 3. An experiment with and independent groups design in which the DV is measured on a ordinal scale 4. A study using a correlational technique in which one measure is interval and the other is ratio. 5. An experiment in which all participants were tested with alcohol and without alcohol on a memory test 6. An experiment in which reaction time was tested using an independent subject design

ANSWERS 1. An experiment with nominal data and an independent groups design chi-squared test 2. Ordinal data on both measures in a study to see if two measures are associated Spearman’s rank correlation / Rho 3. An experiment with and independent groups design in which the DV is measured on a Ordinal scale Mann-Whitney U test 4. A study using a correlation technique in which one measure is interval and the other is ratio Pearsons r 5. An experiment in which all participants were tested with alcohol and without alcohol on a memory test Wilcoxon’s T test 6. 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.