Statistics - Assignment Example

13-6) a) This an observational study. The reason for this is that the researchers don’t assigned choices, they simply observed users. b) The variableis contribution for coffee.c) Increased significantly means in a statistical sense that there is very less probability (Type I error) that the average contribution did not increase above the well-stablished standard.13-16)a) It was an observational study. Because the researchers did not assign women to live near the site of industrial explosion, they simply observed (identified) women who lived near the site of industrial explosion and were under age 40 at that time.b) It was retrospective study.

Because researchers identified subjects who lived near the site of industrial explosion and were under age 40 at that time and collected data on breast cancer developed or not.c) The subject studied were women who lived near the site of industrial explosion and were under age 40 at that time. They were identified.d) The parameter of interest is increase in the incidence of breast cancer in Italy to dioxin released by an industrial accident in 1976.e) The nature and scope of the conclusion the study can reach is that women who lived near the site of industrial explosion and were under age 40 at the time of accident had heightened concentrations of dioxin in their blood and that each tenfold increase in dioxin level was associated with a doubling of the risk of breast cancer.13-38)a) In any experiments, it is required to select sample randomly.

If the subjects were not assigned to the diets randomly instead of letting people pick what they wanted to eat, than there may be possibility of adding another factor (in this case subject’s choice) introduced to the experiments. Thus, it will be difficult to say which factor influenced blood pressure more effectively, subject’s choice what they wanted to eat or diet type. Randomization allows us to equalize the effects of unknown or uncontrollable sources of variation. It does not eliminate the effects of these sources, but it spreads them out across the treatment levels so that we can see past them.b) The meals prepared by the dieticians so that every subject in each group eats same type of diet.c) The researchers need the control group because than they will be able to compare the blood pressure of groups based on different diet only.

If the DASH diet group’s mean blood pressure was lower at the end of the experiment than at the beginning that would only mean that DASH diet lowered the blood pressure. This will not mean how much effective DASH diet is compared to other diets. Further, in an experiment it is required to control sources of variation other than the factors we are testing by making conditions as similar as possible for all treatment groups.d) We would need additional information standard error of difference (or sample standard deviations and sizes for DASH diet group and control group) in order to decide whether an average reduction in blood pressure of 6.

7 points was statistically significant.