I have been discussing this topic all week with people in my department and I can't seem to get a straight answer. I was taught long ago that you should not necessarily transform a variable if the population distribution is expected to be skewed (for use in regression analysis). For example, symptom measures (e.g., posttraumatic stress symptoms, depression symptoms) expected to have a positively skewed distribution in the general population and this is typically what we see in sample data. So, if the population distribution is suppose to be positively skewed and your sample data has the expected positive skew, should you transform that variable? Any clarification on this issue would be greatly appreciated!