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biostatistics

Questions and Answers of Biostatistics

Conclusion Given the body temperatures in the table, what issue can be addressed by conducting a statistical analysis of the data?
Source The listed body temperatures were obtained from Dr. Steven Wasserman, Dr.Philip Mackowiak, and Dr. Myron Levine, who were researchers at the University of Maryland.Is the source of the data
Context of the Data Refer to the table of body temperatures. Is there some meaningful way in which each body temperature recorded at 8 AM is matched with the 12 AM temperature?
Systolic Blood Pressure High systolic blood pressure is 140 mm Hg or higher. (Normal values are less than 120 mm Hg, and prehypertension levels are between 120 mm Hg and 139¤mm Hg.) Subjects with
Gender Selection In a study of the Gender Aide method of gender selection used to increase the likelihood of a baby being born a girl, 2000 users of the method gave birth to 980¤boys and 1020 girls.
There is a 0.3% chance of getting those results by chance. Does the course appear to be effective?
MCAT The Medical College Admissions Test (MCAT) is commonly used as part of the decision-making process for determining which students to accept into medical schools. To test the effectiveness of the
Diet and Exercise Program In a study of the Kingman diet and exercise program, 40 ¤subjects lost an average of 22 pounds. There is about a 1% chance of getting such results with a program that has
Health In a survey of 3014 randomly selected U.S. adults, 45% reported that they have at least one chronic health condition, such as diabetes or high blood pressure. The survey was conducted by
NHANES Examinations In a recent year, the National Health and Nutrition Examination Survey (NHANES), sponsored by the National Center for Health Statistics, selected more than 9000 subjects who were
Clinical Trials Researchers at Yale University conduct a wide variety of clinical trials by using subjects who volunteer after reading advertisements soliciting paid volunteers.
Nuclear Power Plants In a survey of 1368 subjects, the following question was posted on the USA Today website: “In your view, are nuclear plants safe?” The survey subjects were Internet users who
Chocolate An article in Journal of Nutrition (Vol. 130, No. 8) noted that chocolate is rich in flavonoids. The article notes “regular consumption of foods rich in flavonoids may reduce the risk of
Brain Size A data set in Appendix B includes brain volumes from 10 pairs of monozygotic(identical) twins. The data were collected by researchers at Harvard University, Massachusetts General Hospital,
Arsenic in Rice Amounts of arsenic in samples of rice grown in Texas were measured by the Food and Drug Administration (FDA).
Physicians Committee for Responsible Medicine The Physicians Committee for Responsible Medicine tends to oppose the use of meat and dairy products in our diets, and that organization has received
Correlation One study showed that for a recent period of 11 years, there was a strong correlation(or association) between the numbers of people who drowned in swimming pools and the amounts of power
Statistical Significance Versus Practical Significance When testing a new treatment, what is the difference between statistical significance and practical significance? Can a treatment have
Reported Versus Measured In a survey of 1046 adults conducted by Bradley Corporation, subjects were asked how often they wash their hands when using a public restroom, and 70% of the respondents said
Online Medical Info USA Today posted this question on its website: “How often do you seek medical information online?” Of 1072 Internet users who chose to respond, 38% of them responded with
For the data in Exercise 15.11:a. Compute the mean survival time for males using all the observations (including the censoring times).b. Repeat part a for the females.c. Compute the mean survival
Listed below in units of months are the survival and censor times (censoring denoted by a superscripted plus sign) for six males and six females.Males: 1, 3, 4+, 9, 11, 17 Females: 1, 3+, 6, 9, 10,
Using a chi-square test, formally test the goodness of fit of the negative exponential distribution obtained in Exercise 15.9. Test at the 0.05 level of significance.
Again using the data in Exercise 15.7, fit a negative exponential model.Compare it to the Kaplan–Meier curve at the event times 3, 4.5, 11.0, 20.0, and 36.0 months, and decide whether or not the
Using the data in Exercise 15.7, construct a Kaplan–Meier estimate of the survival distribution.
Again, we use the data from Exercise 15.5, but we assume that 6.0, 18.5, and 28 are censor times.a. Estimate the median survival time.b. Why would an estimate of the mean survival time based on
Using the data in Exercise 15.5,a. Calculate a Kaplan–Meier curve for the survival distribution.b. Fit a negative exponential survival model to the data.c. Compare the fitted exponential to the
Suppose the survival times (in months since transplant) for eight patients who received bone marrow transplants are 3.0, 4.5, 6.0, 11.0, 18.5, 20.0, 28.0, and 36.0. Assume no censoring.a. What is the
If the survival times in months for one group are {7.5, 12, 16, 33+, 55, 61}and {31, 60, 65, 76+, 80+, 92} for the second group, apply the chi-square test to see if the survival curves are
If the survival function S(t) = 1 – t/b for 0 t b for a fixed positive constantb, calculate the hazard function h(t) for 0 t b. Recall that F(t) = 1– S(t) and f (t) is the derivative of F
For a negative exponential survival function S(t), recall that S(t) = exp(t), where is the rate parameter or hazard rate function. Consider the conditional probability that the survival time is T
Give definitions of the following terms in your own words and indicate when it is appropriate to use each of them.a. Life tablesb. The Kaplan–Meier curvec. The negative exponential survival
Recall the Lady Tasting Tea example. Suppose that instead of being given four cups with milk poured first and four cups with tea poured first, the lady was given five cups with milk poured first and
Using the modified aggressiveness scores with the aid of the table below, determine Spearman’s rank order correlation for the twins. Aggressiveness Scores for 12 Sets of Identical Twins Twin #1
Apply the sign test to the data in Exercise 14.7. Does the result change?What is the p-value?
Use the modified aggressiveness scores for twins (given in the table below)to apply the Wilcoxon signed-rank test. What is the p-value? Twin #1 (First Born) Twin Set Aggressiveness Twin #2 (Second
Based on the temperature data in Exercise 14.3, use the day pairing to compute a Spearman rank order correlation between the two cities.
Suppose we compare four instructors for consistency of grading. Use the following table to apply the Kruskal–Wallis test to determine whether there is a difference among instructors. Grade Counts
Apply the sign test to the above example. Did the results change? Which test is more powerful, the sign test or the Wilcoxon signed-rank test? Why?
Using the following modification of the city data, apply the Wilcoxon signed-rank test to determine whether there is a difference in average temperature between the two cities. Compare your results
Apply the Wilcoxon rank-sum test in the following case to see if schizophrenia is randomly distributed across the seasons: Season of Birth Among 100 Schizophrenic Patients Season Fall Observed Number
Apply the Wilcoxon rank-sum test to the following problem; we have modified the data from the pig blood loss experiment:Do the results differ from the standard two-sample t test with pooled
The following table shows the home run production of five of baseball’s greatest sluggers over a period of 10 years. Each has hit at least 56 home runs in a season and all but Griffey have had
Analysis of variance may be used in an industrial setting. For example, managers of a soda-bottling company suspected that four filling machines were not filling the soda cans in a uniform way. An
A botanist wants to determine the effect of microscopic worms on seedling growth. He prepares 16 identical planting pots and then introduces four sets of worm populations into them. There are four
Four brands of cereal are compared to see if they produce significant weight gain in rats. Four groups of seven rats each were given a diet of the respective cereal brand. At the end of the
Researchers studied the association between birth mothers’ smoking habits and the birth weights of their babies. Group 1 consisted of nonsmokers.Group 2 comprised smokers who smoked less than one
Using the data from the example in Exercise 13.6 and the ANOVA table from that exercise, determine the p-value for the test (use the F statistic and the appropriate degrees of freedom based on the
Five individuals were selected at random from three communities, and their ages were recorded in the table below. The investigator was interested in determining whether these communities differed in
Using the data from the example in Exercise 13.4 and the ANOVA table from that exercise, determine the p-value for the test (use the F statistic and the appropriate degrees of freedom based on the
Samples were taken of individuals with each blood type to see if the average white blood cell count differed among types. Ten individuals in each group were sampled. The results are given in the
Why does one use a Tukey’s HSD rather than a t test when comparing mean differences in ANOVA?
When a regression model is nonlinear or the error terms are not normally distributed, the standard hypothesis testing methods and confidence intervals do not apply. However, it is possible to solve
Give an example of a logistic regression problem. How is logistic regression different from multiple linear regression?
Discuss the regression toward the mean phenomenon. Give a simple reallife example.
What is stepwise regression? Why is it used?
What is multicollinearity? Why does it occur in multiple regression problems?
When one of the five predictor variables in the preceding example is eliminated from the analysis, the value of R2 drops from 0.75 to 0.71. What does this tell us about the variable that was dropped?
A regression problem with five predictor variables results in an R2 value of 0.75. Interpret the finding.
How does the multiple correlation coefficient R2 for the sample help us interpret a multiple regression problem?
Give an example of a multiple regression problem and identify the terms in the equation.
What is the difference between a simple and a multiple regression equation?
In a study on the elimination of a certain drug in man, the following data were recorded:Intermediate calculations show X = 21, Y = 2.74, X2 = 60.5, Y2 = 0.8526, and X Y = 4.535.a. Plot the scatter
What is logistic regression? How is it different from ordinary linear regression?How is it similar to ordinary linear regression?
Provide the following information regarding outliers.a. What is the definition of an outlier?b. Are outliers indicators of errors in the data?c. Can outliers sometimes be errors?d. Give an example of
An investigator studying the effects of stress on blood pressure subjected mine monkeys to increasing levels of electric shock as they attempted to obtain food from a feeder. At the end of a 2-minute
In the text, a correlation matrix was described. Using your own words, explain what is meant by a correlation matrix. What values appear along the diagonal of a correlation? How do we account for
An experiment was conducted to study the effect on sleeping time of increasing the dosage of a certain barbiturate. Three readings were made at each of three dose levels:Sleeping Time (Hrs) Dosage
Refer to Table 12.14:a. Create a scatter diagram of the relationships between age (X) and cholesterol(Y), age (X) and blood sugar (Y), and cholesterol (X) and blood sugar(Y).b. Calculate the
Refer to Table 12.1 in Section 12.3. Calculate r between systolic and diastolic blood pressure. Calculate the regression equation between systolic and diastolic blood pressure. Is the relationship
A psychiatric epidemiology study collected information on the anxiety and depression levels of 11 subjects. The results of the investigation are presented in Table 12.13. Perform the following
Some epidemiologic studies have reported a negative association between moderate consumption of red wine and coronary heart disease mortality.To what extent does this correlation represent a causal
In a study of coronary heart disease risk factors, an occupational health physician collected blood samples and other data on 1000 employees in an industrial company. The correlations (all
List the criteria that need to be met in order to apply correctly the formula for the Pearson correlation coefficient.
Research papers in medical journals often cite variables that are correlated with one another.a. Using a health-related example, indicate what investigators mean when they say that variables are
Give in your own words definitions of the following terms that pertain to bivariate regression and correlation:a. Correlation versus associationb. Correlation coefficientc. Regressiond. Scatter
A multiphasic health examination was administered to 1000 employees of a pharmaceutical firm. 50% of these employees had elevated diastolic blood pressure and 45% had hypoglycemia. A total of 37% of
In the community health survey, the investigators studied the relationship between alcohol drinking status (defined according to four categories) and smoking status (defined according to three
In the same community health survey, the investigators wanted to know whether smoking status varied according to race/ethnicity. Race was measured according to five categories (African American,
In the community health survey described in the previous exercise, respondents’smoking status was classified into three categories (smoker, quitter, never smoker). Table 11.17 shows the results for
In a community health survey, individuals were randomly selected for participation in a telephone interview. The study used a cross-sectional design.Table 11.16 shows the results for the
Researchers at an academic medical center performed a clinical trial to study the effectiveness of a new medication to lower blood sugar. Diabetic patients were assigned at random to treatment and
A hospital accrediting agency reported that the survival rate for patients who had coronary bypass surgery in tertiary care centers was 93%. A sample of community hospitals had an average survival
State in your words definitions of the following terms:a. Chi-squareb. Contingency table (cross-tabulation)c. Correlated proportionsd. Odds ratioe. Goodness of fit testf. Test for independence of two
An epidemiologic study examined risk factors associated with pediatric AIDS. In a small study of 30 cases and 30 controls, a positive history of substance abuse occurred among 11 of the cases and 6
A longitudinal study of occupational status and smoking behavior among women reported at baseline that 170 per 1000 professional/managerial women were nicotine dependent. The corresponding rate among
In a British study of social class and health, a total of 171 out of 402 lower social class persons were classified as overweight. The percent of overweight persons in the general population was 39%.
For the data in Exercise 10.5, compute a 99% confidence interval using the normal approximation with continuity correction. Is the result close to the exact interval found in Exercise 10.6? Explain
Calculate an exact 95% confidence interval for the proportion of edentulous persons in the Latin American village (refer to Exercise 10.5.)
A dental researcher investigated the occurrence of edentulism (defined in the research study as loss of two or more permanent teeth, not including loss of prophylactically extracted wisdom teeth) in
Referring to Exercise 10.2, construct an approximate 95% confidence interval for the difference between the proportions of patients affected by peripheral neuropathy in the control group and in the
Construct exact 95% confidence intervals for the proportion of patients with peripheral neuropathy in the medication group and the proportion of patients in the control group in the previous
Peripheral neuropathy is a complication of uncontrolled diabetes. The number of cases of peripheral neuropathy among a control group of 35 diabetic patients was 12. Among a group of 11 patients who
Give definitions of the following terms in your own words:a. Sample proportionb. Population proportionc. Binomial variabled. Bernoulli triale. Continuity correctionf. Confidence interval for a
Here are some questions about hypothesis testing:a. Describe the one sample test of a mean when the variance is unknown and when the variance is known.b. Describe the use of a two-sample t test
Define sensitivity and specificity. How do they relate to the type I and type II errors in hypothesis testing?
Why can missing data be a problem in data analysis? What is imputation?
How do Bayesians treat parameters? How do frequentists treat parameters?Are the two approaches different from one another?
What is Bayes’ theorem? Define prior distribution. What is a posterior distribution?
What is a meta-analysis? Why are meta-analyses performed?

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