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Among a group of disabled women aged 65 and older who were tracked for several years, those who had a vitamin B12 deficiency were twice as likely to suffer severe depression as those who did not. Which statement is true?This is a completely randomized experiment.This is a randomized blocked experiment.This is an example of a surveyThis is an observational study.A farmer wishes to determine which of two brands of baby pig pellets, Kent or Moormans, produces better weight gains. Two of his sows each give birth to litters of 10 pigs on the same day, so he decides to give the baby pigs in litter A only Kent pellets, while the pigs in litter B will get only Moormans pellets. After four weeks, the average weight gain for pigs in litter A is greater than the average weight gain for pigs in litter B. What does the brand of pellets represent? *an extraneous variablea dependent variablethe response variablethe factorSome medical investigations have indicated that nonsmokers are more likely to develop Alzheimer's disease than smokers. Assuming these investigations were carefully done, what is the most reasonable conclusion? *These were probably observational studies; therefore, no conclusion about smoking providing protection against Alzheimer's is proper.Given that these were carefully done, they probably were experiments and thus they do show that smoking provides protection against Alzheimer's.Without information about use or nonuse of randomization, no conclusion about cause and effect is possible.No matter how carefully the investigation were done, no conclusion is possible without knowing the sample size. ...