Chi squared and Wilcoxon rank sum test Flashcards
when is chi squared test used
when comparing population proportions in a contingency table
what is fo
observed frequency
what is fe
expected frequency
when to reject null hypothesis in chi squared test for equal proportions
if chi squared stat > level of significance
what is overall proportion (p hat)
(x1 + x2)/(n2 + n1)
how to get expected frequencies
total amount x expected proportion
how to calculate chi squared stat for equal proportion
sum of all (observed frequency - expected frequency)^2 / fe
degrees of freedom for chi squared
(r-1)x(c-1)
fe for chi squared test for independence
(row total x col total)/n
what are the two versions of the wilcoxon rank test
when samples are less than 10 and greater than 10
steps in wilcoxon rank sum test (n < 10)
- Assign ranks to combined sample observation
- Assign average rank for ties
- Sum the ranks in each sample
- Obtain test stat from smaller sample
- Reject null hypothesis if smaller sum is between the upper and lower limit
what does wilcoxon rank test test for
equal medians
what test can be used to test the equality of more than 2 population medians
kruskal wallace rank test
steps in kruskal wallace rank test
- obtain ranking
- sum rankings
- compute the H stat
excel formula to get chi squared critical value
CHISQ.INV.RT(lvl of sig, deg freedom)
if chi sqaured stat > chi squared critical value reject null hopthesis
