Sophia Introduction to Statistics Unit 1 Milestone 1

Several scientific and statistical studies have been done to determine whether or not pollutants in soil increase the incidence of cancer. A study based on many previous studies summarizes that there is no link between pollutants in soil and cancer. This kind of statistical study is called a __________. Clinical trial Prospective study Matched-pair design Retrospective study RATIONALE Since the data has already been collected it is called a retrospective study design. CONCEPT Prospective and Retrospective Studies 2 The blood bank at a hospital has 1,200 units of blood, out of which 37% units are of blood group B+. A clinical researcher randomly selects 300 units of blood and finds that 33% of those are of blood group B+. To test his result, he randomly selects 200 units of blood and finds that 40% of those are of blood group B+. Which of the following is the reason there is a difference between the two percentages selected by the researcher? Random error; the numbers were different due to variability inherent in sampling. Both samples suffered from non-response bias. The samples were not random samples. The sample sizes were both too small. RATIONALE