A hasty generalization is a conclusion based on a small sample size, rather than looking at statistics that are much more in line with the typical or average situation.
A sample of hasty generalization is when FDR says in his speech that the attack yesterday on the Hawaiian Islands has caused severe damage to American naval and military forces. I regret to tell you that very many American lives have been lost. FDR based this conclusion on what probably was told but not even the military at Pearl Harbor knew the exact numbers of deceased but several day later.