lesson 10 - Factors Affecting Choice Of Statistical Tests Flashcards
What are descriptive statistics
Descriptive statistics can give summaries of data that we have collected from our research; and an indication of what the statistical that we can correctly select the most appropriate statistical test to analyse our results
analysis might reveal about our results. Levels of Measurement are used to try to categorise our data into one of four types, so
Nominal data
The data consists of the numbers of participants that might fall into different categories, and a person can be placed in one category only and not the other
Eg How many people in your sample are either male or female
Ordinal data
The data can be placed in rank order from lowest to highest. The ordinal scale can consist of measurements that are of unequal intervals e.g. 1.20, 1.25, 1.27.
The data is concerned with the order that the data can be presented in.
Eg The order from lowest to highest in terms of how quickly participants finished a 100 metre
swimming race, 1st, 2nd, 3rd etc.
Interval data
The data has fixed and even intervals (and this differs from ordinal data). The units of data are fixed (and have the same distance) throughout the range.
Eg Examples include height and weight which all have fixed intervals between each unit of measurement
What are the non parametric tests
Chi squared
2) Spearman’s Rho
3) Mann Whitney
4) Wilcoxon
What are the parametric test
Pearson sr
6) Related t-test
7) Unrelated t-test
What are parametric tests
Parametric tests are more robust and powerful than non-parametric tests. They rely on the actual data collected rather than just examining the rank order of the data. Parametric tests are also more likely to detect if the data is significant or not.
What are the 3 factors that mean a parametric test can be conducted
Interval level of measurement:
The data must be interval rather than ordinal in terms of level of measurement
b) Normal distribution:
The data collected should be taken from a population that shows a normal distribution curve rather than a skewed distribution
c) variance of data
The data should have similar variance or spread of scored. This can be examined by looking at the dispersion of data and the standard deviations for both conditions and seeing if they are similar
What are the three questions you ask to decide which test to use
Does the research involve a correlation, a test of difference, or an association?
If using a correlation then you should use Spearman’s Rho or Pearson’s r
If looking for a test of difference, then you should use one of these tests Mann Whitney, Chi Squared, Wilcoxon, Unrelated t-test, or Related t-test
• •If looking for an association between variables then you would use Chi squared
2) Which research design is being used?
•••
Independent measures
Repeated measures or
Matched participants design
3) Which level of measurement is being used in the research?
• Decide between nominal, ordinal and interval
When would you use each of the tests
Chi squared - test of difference, independent measures, nominal, non parametric
Mann Whitney U test - test of difference, independent measures, ordinal, non parametric
Unrelated T test - test of difference, independent measures, interval, parametric
Sign test - test of difference, repeated measures/mayched pps design, nominal, non parametric
Wilcoxon- test of difference, repeated measures/mayched pps design, ordinal, non parametric
Related T test - test of difference, repeated measures/mayched pps design, interval, parametric
If it’s a test of association use chi squared
If it’s correlation us spearman’s rho if ordinal data and pearsons r if interval data
