Posted by Anonymous on Thursday, November 16, 2006 at 10:56pm.
1)A nutritionist wants to study the effect of storage time (6, 12, and 18 months) on the amount of vitamin C present in freeze dried fruit when stored for these lengths of time. Vitamin C is measured in milligrams per 100 milligrams of fruit. Six fruit packs were randomly assigned to each of the three storage times. The treatment, experimental unit, and response are respectively:
(a) A specific storage time, amount of vitamin C, a fruit pack
(b) A fruit pack, amount of vitamin C, a specific storage time
(c) Random assignment, a fruit pack, amount of vitamin C
(d) A specific storage time, a fruit pack, amount of vitamin C
(e) A specific storage time, the nutritionist, amount of vitamin C 2.
We wish to investigate if a new medicine is effective in reducing the length and severity of the flu. We take the next 20 patients that come to the walk-in clinic complaining of flu and, after a medical exam to verify that the patients do have the flu, we give them the new medicine and tell them about the new drug we are giving them. One week later, the patients are contacted and 15 patients state the new remedy was helpful in reducing the severity and length of the illness. Which of the following is not correct?
(a) This is a poor experiment because there is no control group. We do not know how many would feel better in a week without treatment.
(b) This is a poor experiment because it is not double-blinded. The patients may feel relief because they thought the drug should work.
(c) This is a poor experiment because a convenience sample was selected. Patients who come to the walk-in clinic may have more severe flu than people who do not.
(d) This is a poor experiment because we didn't give the remedy to people without the flu to assess its effect in a control group.
(e) This is a poor experiment because the sample size is likely to be too small to detect anything but a gross improvement in measuring the proportion of people reporting an improvement.
3. An experiment to measure the effect of giving growth hormones to girls affected by Turner’s Syndrome was carried out recently in Vancouver. All 34 girls in the study were given the growth hormone and their heights were measured at the time the hormone was given and again one year later. No measurements were made on their final adult heights. Which of the following is not a problem with this experiment:
(a) There was no blinding
(b) There was no control group
(c) Nonresponse bias
(d) There was insufficient attention to the placebo effect
(e) Because final heights were not measured, it would be impossible to tell if the hormone affected final height or only accelerated growth and made no difference to final height.
4. A survey is to be undertaken of recent nursing graduates in order to compare the starting salaries ofwomen and men. For each graduate, three variables are to be recorded (among others) sex, startingsalary, and area of specialization.
(a) Sex and starting salary are explanatory variables; area of specialization is a response variable.
(b) Sex is an explanatory variable; starting salary and area of specialization are response variables.
(c) Sex is an explanatory variable; starting salary is a response variable; area of specialization is a possible confounding variable.
(d) Sex is a response variable; starting salary is an explanatory variable; area of specialization is a possible confounding variable.
(e) Sex and area of specialization are response variables; starting salary is an explanatory variable.
5. A researcher wishes to compare the effects of 2 fertilizers on the yield of a soybean crop. She has 20 plots of land available and she decides to use a paired experiment — using 10 pairs of plots. Thus, she will:
(a) Use a table of random numbers to divide the 20 plots into 10 pairs and then, for each pair, flip a coin to assign the fertilizers to the 2 plots.
(b) Subjectively divide the 20 plots into 10 pairs (making the plots within a block as similar as possible) and then, for each pair, flip a coin to assign the fertilizers to the 2 plots.
(c) Use a table of random numbers to divide the 20 plots into 10 pairs and then use the table of random numbers a second time to decide upon the fertilizer to be applied to each pair.
(d) Flip a coin to divide the 20 plots into 10 pairs and then, for each pair, use a table of randomnumbers to assign the fertilizers to the 2 plots.
(e) Use a table of random numbers to assign the 2 fertilizers to the 20 plots and then use the table of random numbers a second time to place the plots into 10 pairs.
7. A properly conducted random survey selected 1000 Canadians (from a total population of about 30 million) and 1000 Americans (from a total population of about 300 million). Which of the following is false?
(a) Randomization ensures that both samples are representative of their respective populations.
(b) The precision is determined by the ratio of the sample size to the total population size.
(c) A smaller proportion of the American population has been chosen. Therefore, a particular person has a smaller chance of being selected in America than in Canada.
(d) A potential stratification variable for both countries could be location — eastern, middle, or western continental.
(e) Random digit dialing to select people for the survey could induce biases in the results if the characteristic of interest for the survey is related to income.
8. Consider an experiment to investigate the efficacy of different insecticides in controlling pests and their effects on subsequent yield. What is the best reason for randomly assigning treatment levels (spraying or not spraying) to the experimental units (farms)?
(a) Randomization makes the experiment easier to conduct since we can apply the insecticide in any pattern rather than in a systematic fashion.
(b) Randomization will tend to average out all other uncontrolled factors such as soil fertility so that they are not confounded with the treatment effects.
(c) Randomization makes the analysis easier since the data can be collected and entered into the computer in any order.
(d) Randomization is required by statistical consultants before they will help you analyze the experiment. (e) Randomization implies that it is not necessary to be careful during the experiment, during data collection, and during data analysis.
1) I would go with d)
2) Is "all of the above" an option?
3) I would go with c) also.
4) I would go with c) also.
5) Im not sure what the question is asking, and I, quite frankly, do not see the difference between some of the answers. A coin flip and a table of random numbers should be equally random, and therefore statistically equivalent.
7) Tough one. They all seem true. I would go with b). Precision is also related to the underlying variance of the population. I suggest you research this one a little more.
8) I too would go with b)
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