Lecture 5

We discussed normal plots for assessing normality of data. Normal probability plots are under Stat > Basic Statistics > Normality Test.

From the shape of the plot, you can tell if your data are normal, right-skewed, or heavy-tailed.

Often, for right-skewed data, a log-transformation of the data is helpful. We discuss the transformation, the change from a multiplicative to an additive scale, and the interpretation of results after a log-transformation.

Data: Originally from Kapitulnik at al. 1976, used in Biostatistics by van Belle et al. The data are the rate of metabolism (nmol 3H₂O formed/g per hour) of the drug zoxazolamine in the placentas of women who smoked and who didn't smoke during pregnancy.

NonSmoker	Smoker
0.18	0.66
0.36	0.60
0.24	0.96
0.50	1.37
0.42	1.51
0.36	3.56
0.50	3.36
0.60	4.86
0.56	7.50
0.36	9.00
0.68	10.08
	14.76
	16.50