Answer:
D) An observational study based on available data.
Step-by-step explanation:
This is an observational study based on available data.
If it had been on a sample, he would take a sample of a few pitchers, and not studied the statistics of all major league pitchers during those seasons.
It is not an anecdotal evidence, because an anecdotal evidence is something without study, just an impression.
It is not an experiment, because he just studies(observes, that is why it is an observational study) the data, he does not change anything about the pitchers.
So the correct answer is:
D) An observational study based on available data.