26. Missing values
Remove the cases with unknowns
Fill in the unknown values by exploring the properties of the variable
Fill in the unknown values by exploring the correlations between
variables
Fill in the unknown values by exploring the similarity between cases
27. Transformations of the response
and explanatory variables
Linearize the relationship between the response and the explanatory
variables
logy against x for exponential relationships;
logy against logx for power functions;
expy against x for logarithmic relationships;
1/y against 1/x for asymptotic relationships;
logp/1−p againstx for proportion data.
Other transformations are useful for variance stabilization:
√y to stabilize the variance for count data;
arcsin(y) to stabilize the variance of percentage data.