Statistical tests

Test types

measurements → collecting data that are measurements

→ Correlation - looking for relationship between measurements

→ Student T test - differences between measured data

Frequencies

→ Chi squared test - collecting data about the number of individuals in particular categories

Student t test

Mean of group 1 values - mean of group 2 values / (standard deviation/number in sample of 1) + (standard deviation/number of sample 2)

degrees of freedom is (number in sample 1 -1) + (number in sample 2-1)

Comparing stat test to critical value

Test statistic is more than crit value → reject null hypothesis → less then 0.05 probability that it’s due to chance → significant difference between…

Test stat is less than crit value → accept null hypothesis → more than 0.05 probability its due to change → no significant difference between…

Correlation

Spearman’s rank

1-( 6 x sum of difference in ranks between data pairs / total number of pairs (total number of pairs squared -1)

Chi squared

x squared = (frequencies observed - frequencies expected) squared / frequencies expected