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Lecture 8

PSYC 305 Lecture Notes - Lecture 8: Null Hypothesis, Random Assignment, Type I And Type Ii Errors

Course Code
PSYC 305
Heungsun Hwang

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PSYC305 Lecture 8 - Feb. 1
One-Way ANOVA:
Assume all three populations all have the same variances
Assessing Normality:
Look at descriptive statistics
Skewness 0
> 0 - positively/right skew
< 0 - negative/left skew
Look at their standard errors
If it is normally distribution, there is no skewness
If it is skewed, technically you can’t apply the one-way ANOVA
Construct charts
Separate histograms for each group to assess normality
It doesn’t have to be perfect, just roughly symmetric
Evaluate a normal quantile plot (or normal probability plot)
Sort observations from smallest to largest
Calculate the z-scores of the sorted observations
Plot the observations against the corresponding z-scores
If the data are closed to normal, then the points will lie close to some straight
Statistical tests of normality:
The Kolmogorov-Smirnov (K-S) test
The Shapiro-Wilk test
Compares sample scores to a set of scores generated from a normal distri-
bution with the sample means and standard deviation
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