W12 non-parametric tests Flashcards
(16 cards)
if assumptions violated: not normally distributed…
use non-parametric
Null vs alternate hypothesis for CORRELATIONS
pearsons r null = no relationship
alternate =there is relationship
non-parametric pros + cons
pros = robust, ease of interpretation
cons = less power, limited precision
NON-PARAMETRIC tests include:
Chi-square = for t-test, ANOVA
Spearman’s Rho = correlation
z,t,ANOVA rely on PARAMETRIC assumptions like:
- continuous - interval or ratio
- normally distributed
- homogeneity (levenes) or sphericity (muachelys)
Assumptions are violated if…
- non-normally dist (skewed, bimodal)
- categorical (nominal or ordinal)
- variances wildly dissimilar across IV
Violating assumptions = bad because…
- not real result – false positive type 1 error
- miss a result – false negative type 2 error
- unreliable pvalue/intervals
Chi-Square Xsquared
tests if theres a significant difference in frequency we’d expect, and observe to happen
Two types of Chi Square
- Goodness of fit - if single cate variable fits in expected distribution
- test of independence - if 2 categorical variables are related
Chi Square
goodness of fit H0 and H1
H0 null is observed = expected
H1 is observed is NOT = expected
GOOD FIT formula
find value of xsquared then go to table
df = k(number of groups) -1
df on side column, 0.05on row
if obtained is bigger, reject null hypothesis
INDEPENDENCE
when you know observed but not expected – need to calculate it
row total x column total
divided by
grand total all cells
Assumptions for Chi Square:
- categorical data
- independence of observation - each participant appear once
- expected frequencies (at least 5 each cell)
- sample size - large
Spearmans’ Rho
- nonparametric
- measure strength, direction of association between 2 variables
- data = ranked Ordinal likert scales
- range -1 to 1
RULES: When to use spearman’s rho
- at least one variable is ordinal
- data not normally distributed or has outliers
- relationship is non-linear
non-linear monotonic relationship is
- moves in one direction (not at constant rate)