Lecture 4 Normal distribution? Sample data at :

List of nice things Equal variance Normal distribution Independent variables Linear relationship

Example 1 Is there a relation between the number of apples given to a teacher and the grade given by a teacher? Normality? –Standadized residuals –P-P plots (Q-Q plots) –Does it look nice?

Kolmogorov-Smirnov test Tests if a sample of variables are normal. Tests if the observed distribution function S(x) is significantly different from a hypothetical distribution function F(x). Lilliefors modification because F(x) is estimated from S(x).

Example 2 Is there a relation between the number of muffins given to a teacher and the grade given by a teacher?

Transformations Most statistical models are linear. Equal variance. c = 1: No transformation c = -1: reciprocal c = ½ : square root c = 0: logarithmic

Outliers Tjeck the data Tjeck the labbook Trimmed mean Common sense and your vast experience