Biostats Final Exam Review | Complete Solution

Question 1
The following data were collected in a clinical trial to compare a new drug to a placebo for its effectiveness in a lowering total serum cholesterol. Generate a 95% confidence interval for the difference in mean total cholesterol levels between treatments.
    New Drug (n=75)    Placebo (n=75)    Total sample (n=150)
Men (SD) Total Serum Cholesterol     185.0 (24.5)    204.3 (21.8)    194.7 (23.2)
% patients with Total Cholesterol < 200    78.0%    65.0%    71.5%

A. Upper limit
B. Lower limit
C. Based on the confidence interval which of the following is (are) true? (a) There is significant evidence, alpha = 0.05, to show that there is a difference in total serum cholesterol between treatments New Drug and Placebo (b) There is not significant evidence, alpha = 0.05, to show that there is a difference in total serum cholesterol between treatments New Drug and Placebo (c) The difference between total cholesterol between treatments New Drug and Placebo is essentially 0 (d) b and c.
Question 2
A study is designed to investigate whether there is a difference in response to various treatments in patients with rheumatoid arthritis. The outcome is patient’s self-reported effect of treatment. The dada are shown below. Are symptoms independent of treatment? Conduct a ChiSquare test at a 5% level of significance.
    Symptoms Worsened     No Effect    Symptoms Improved    Total
Treatment 1    22    14    14    50
Treatment 2    14     15    21    50
Treatment 3    9    12    29    50

A. df
B. critical value
C. computed statistics
Based on comparing the computed statistics to the critical value which of the following is (are) true? (a) There is significant evidence, alpha = 0.05, to show that treatment and response are not independent (b) there is not significant evidence, alpha = 0.05, to show that treatment and response are not independent (c) there is significant evidence, alpha = 0.05, to show that treatment and response are independent (d) b and c
Question 3
An investigator conducts a study to investigate whether there is a difference in means PEF in children with chronic bronchitis as compared to those without. Data on PEF are collected and summarized below. Based on the data, is there statistical evidence of a lower mean PEF in children with chronic bronchitis as compared to those without? Apply the two sample t test at alpha = 0.05.
Group    Number of children    Mean PEF    Std Dev PEF
Chronic Bronchitis     25    281    68
No chronic bronchitis     25    319    74

1. z 95% confidence interval =
2. Upper limit 95% CI =
3. Lower limit CI 95% =
4. Based on comparing the critical the upper and lower limits of the confidence interval for the mean of PEF for children with no Chronic Bronchitis to the mean PEF for children with bronchitis which of the following is (are) true? (a) There is statistical evidence of a lower mean PEF in children with chronic bronchitis as compared to those without (b) There is NOT statistical evidence of a lower mean PEF in children with chronic bronchitis as compared to those without (c) The confidence interval contains the mean PEF for the No chronic bronchitis group (d) a and c
Question 4
The following are body mass index (BMI) scores measured in 12 patients who are free of diabetes and particularly in a study of risk factors for obesity. Body mass index is measured as the ratio of weight in kilograms to height in meters squared. Generate a 95% confidence interval estimate of the true BMI. 25, 27, 31, 33, 26, 28, 38, 41, 24, 32, 35, 40
Upper limit of CI =
Lower limit of CI =
8. Which of the following is true?
a. if a 90% CI for the mean is (75.3 to 80.9), we would reject HO: Mean=70 in favor of H1; Mean ≠70 at alpha= 0.05 (b) If a test is run and p=0.0356, then we can reject HO at alpha = 0.01 (c) If a 95% CI for the difference in two independent means is (-4.5 to 2.1), then the point estimate is -2.1 (d) If a 95% CI for the difference in two independent mean is (2.1 to 4.5), there is no significant difference in means (e) The margin of error is always greater than or equal to the standard error
Question 5
A randomized controlled trial is run to evaluate the effectiveness of a new drug for asthma in children. A total of 250 children are randomized to either the new drug or placebo (125 per group). There are 63 boys assigned to the new drug group and 58 assigned to the placebo. Is there a statistically significant difference in the proportion of the boys assigned to the treatments? Apply the appropriate test at a 5% level of significance (1) Critical value = +/- (2) computed statistics (3) Based on comparing the computed statistics to the critical value which of the following is (are) true? (a) There is significant evidence, alpha =0.05, that there is a difference in the proportions of boys assigned to the treatments (b) There is not significant evidence, alpha =0.05, that there is a difference in the proportions of boys assigned to the treatments (c) Statistically speaking the difference in the proportions of boys assigned to the treatment is 0 (d) b and c.
Question 6
A clinical trial is conducted to investigate the effectiveness of an experimental drug in reducing preterm delivery to a drug consigned standard care and to placebo. Pregnant women are enrolled and randomly assigned to receive either the experimental drug, the standard drug or placebo. Women are followed through delivery and classified as delivery preterm (>37 weeks) or not The data are shown below.
Is there a statistically significant difference in the proportions of women delivery preterm among the THREE treatments groups? Apply the test of 5% level of significance.
1 df =
2. critical value =
3. computed value =
4. based on comparing the computed chi square with the critical values for the Chi square which of the following is (are) true?
(a) there is statistically significant difference in the proportions of women delivering preterm among the three treatments groups (b) there is not statistically significant difference in the proportions of women delivering preterm among the three treatments groups (c) the proportion are statistically the same (d) a and c
Preterm delivery     Experimental drug     Standard drug    Placebo
Yes    17    23    35
No    83    77    65

Question 7
The table below summarizes baseline characteristics of patients participating in a clinical trial. Which, if any, baseline characteristics are significantly different (at the 0.05 level of significance) between treatment groups (a) age (b) Total cholesterol (c) Diabetes (d) % female (e) a and b (f) c and d
Characteristic    Placebo (n=125)    Experimental (n=125    P
Men (+ - SD) age    54 + - 4.5    53 + - 4.9    0.7856
%female    39%    52%    0.0289
% less than high school education    24%    22%    0.0986
%  completing high school    37%    36    
% completing some college     39%    42%    
Mean (+ - SD) Systolic blood pressure    136 + - 13.8    134 + - 12.4    0.4736
Mean (+ - SD) total cholesterol     214 + - 24.9    210 +- 23.1     0.8954
% current smokers     17%    15%    0.5741
% with diabetes     8%    3%    0.0438

Question 8
An investigator conducts a study to investigate whether there is a difference in mean PEF in children with chronic bronchitis are compared to those without. Data on PEF are collected and summarized below. Based on the data, is there statistical evidence of a lower mean PEF in children with chronic bronchitis as compared to those without? Apply the appropriate test at alpha = 0.05
1. critical value =
2. computed t =
3. Based on comparing the critical t value to the computed t value which of the following is (are) true? (a) There is statistical evidence of a lower mean PEF in children with bronchitis as compared to those without (b) There is NOT statistical evidence of a lower mean PEF in children with bronchitis as compared to those without (c) There are not enough data points to reach a conclusion (d) b and c.
Group     Number of children    Mean PEF    STD Dev PEF
Chronic Bronchitis    25    281    68
No chronic bronchitis     25    319    74

Question 9
Peak expiratory flow (PEF) is a measure of a patient’s ability to expel air from the lungs. Patients with asthma or other respiratory conditions often have restricted PEF. The mean PEF for children free of asthma is 306. An investigator wants to test whether children with chronic bronchitis have restricted PEF. A sample of 40 children with chronic bronchitis are studied and their means PEF is 279 with a standard deviation of 71. Is there statistical evidence of a lower mean PEF in children with chronic bronchitis? Apply the appropriate test at alpha = 0.05
1. critical value =
2. computed z =
3. based on comparing the critical z value to the computed z value which of the following is (are) true? (a) There is statistically significant evidence at alpha = 0.05 to show a lower mean PEF in children with chronic bronchitis (b) There is NOT statistically significant evidence at alpha = 0.05 to show a lower mean PEF in children with chronic bronchitis (c)There are not enough data points to reach a conclusion (d) b and c
Question 10
The line of best fit can be defined as:
 A. a line through a scatterplot that maximizes the distance from the line and the individual scatter plot points.
B a line through a scatterplot that minimizes the distance from the line and the individual scatter plot points.
 C A scatter plot of the results of substituting independent variables into the regression equation
 D a and a
 E b and c
Question 11
An investigator wants to assess whether the use of a specific medication given to infants born prematurely is associated with developmental delay, fifty infants who were given the medication and fifty comparison infants who were also born prematurely but not given the medication will be selected for the analysis. Each infant will undergo extensive testing at age 2 for various aspects of development. Identify the type of study