Anecdotal evidence: individual cases that are striking in some way and occur rarely that needs not to be represented for any large group of cases. Ex: friends are big fans the show barney , this cant be generalized to a larger population. This is because any group of friends cannot be used as a representative for all college students. Available data: data produced in the past for some other purpose but may help answer a present question. Statistical designs for producing data rely on either sampling or experiments. The idea of sampling is to study a part (sample) in order to gain information about the whole (population) Data are often produced by sampling a population of people or things. Census attempt to contact every individual in the entire population. Carefully conducted sample is better than a census. Observational study: individuals are observed and variables of interest are measured but do not attempt to influence the responses.