In the following observational studies, describe changes that could be made to the data collection process that would result in an experiment rather than an observation study. Also, offer suggestions about unseen biases or lurking variables that may be present in the studies as they are described here.
a. In a sample of 50 members of a local health club you find that 12 of these members meet weekly with a physical fitness trainer and that the average body mass index (BMI ) of these 12 members is less than the average BMI of the other 38 club members in your sample.
b. In a sample of 12 bank tellers at a local branch office, the 7 tellers who have completed the advanced training program offered by the bank have a lower average error rate in the processing of transactions than the remaining 5 tellers.