statistical tests Flashcards
define null hypothesis
this is the prediction you want to test
you assume the null hypothesis is true
define significance level
this is the level of proof you are looking at before you read into your results
the smaller the significance level, the stronger the evidence you’re looking for that your results are not just down to chance
if the probability of your results being a fluke is less than the significance level…
you can suggest that your null hypothesis was not true. you can then assume that the difference between groups was down to the change you made in your independent variable.
you reject the null hypothesis and assume your alternative hypothesis is true.
your results are therefore statistically significant
if the probability of your results being a fluke is more than the significance level…
you accept the null hypothesis and reject the alternative hypothesis as it means that your results could have occurred by chance.
assumptions of the sign test
- test of difference
- repeated measures
- nominal data (categories)
how to carry out the sign test
- Calculate difference between before and after.
- Add up positive signs and negative signs, ignore no change.
- The smallest one is the observed value.
what key pieces of information do you need for the sign test?
- significance level desired
- number of participants (N value)
- identify whether its a two-tailed or one-tailed test
assumptions of the Mann Whitney test
- test of difference
- independent groups
- ordinal data (scores)
how to carry out the Mann Whitney U test?
- rank both sets of data together (1 being the lowest)
- add up the sum of both groups
- work out value of U –> U = sum - (N(N+1))/2
- use smallest value
- use critical value table to find critical value
- draw conclusion: if the U value > critical value = must accept null hypothesis
what key pieces of information do you need for the sign test?
- no. of participants for both groups
- value of U
- critical value table
assumptions of the Wilcoxon test
- test of difference
- repeated measures
- ordinal data
how to carry out the Wilcoxon test?
- calculate the difference before and after
- rank the absolute difference (leaving out differences of 0)
- calculate value of T –> T = sum of the less frequent sign
- draw conclusions: T value < critical value = accept the null hypothesis
what key pieces of information are needed to carry out the Wilcoxon test?
- critical value table
- table of results
- significance level
- one or two tailed tests
- no. of participants
assumptions of spearman’s rho
- test of relationship/ association
- ordinal data
- correlation
how to calculate spearman’s rho?
- rank both columns from N (no of participants) - 1 (1 being the largest)
- calculate the difference between the two and square each value
- find the sum of D^2
- calculate value of Rho –> Rho = (1-6Σd^2)/ (N^3-N)
- draw conclusions: Rho > critical value = data is significant
