Chapter Problems: Power Sample Size & Multivariate

20 questions, 30 points

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Chapter 8 Chapter 9

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Chapter 08

Multiple Choice

  1. A researcher is conducting a study to determine the mean trough dosage of medication for a population. Assuming a previous study was conducted for the same medication and the mean trough dose was found to be 490 mg with a standard deviation of 50 mg, calculate the margin of error for a 95% confidence interval assuming the previous study enrolled 600 individuals.
    A) E = ± 4.19
    B) E = ± 63.57
    C) E = ± 4.00
    D) E = ± 0.27
  2. A researcher is conducting a study to determine the mean trough dosage of medication for a population. Assume a previous study was conducted for the same medication and the mean trough dose was found to be 300 mg with a standard deviation of 30 mg. If the researcher wants to be 95% confident the true mean trough dosage of the medication is within 10 mg of the true mean trough dosage, what sample size is needed?
    A) n = 35
    B) n = 23
    C) n = 47
    D) n = 62
  3. A researcher is conducting a study to determine the mean trough dosage of medication for a population. Assume a previous study was conducted for the same medication and the mean trough dose was found to be 490 mg with a standard deviation of 30 mg. If the researcher wants to be 95% confident the true mean trough dosage of the medication is within 10 mg of the true mean trough dosage, what sample size is needed if the study is predicted to have an 76% retention rate?
    A) n = 50
    B) n = 71
    C) n = 47
    D) n = 104
  4. A researcher wants to calculate the prevalence of Alzheimer’s among members of a specific community who are 65 years of age and older. The researcher needs to know how many individuals who are 65 years of age or older need to be recruited for the study to ensure the estimated prevalence will be within 1.0% of the true proportion. Calculate the sample size needed by the researcher if a national study has shown 10.73% of individuals 65 years of age have Alzheimer’s based on a 95% CI of the true proportion.

A) n = 152
B) n = 1010
C) n = 2673
D) n = 3680

  1. A clinical trial is being conducted in order to determine the efficacy of a new drug that will be used to treat rheumatoid arthritis. The efficacy of the medication will not only be determined by the physical improvement of symptoms but will also be determined by using a blood test to examine the concentration of C-reactive protein (an inflammatory marker) in an individual’s blood. If the researcher wants a margin of error for the level of C-reactive protein to be less than or equal to 1.5 mg/d and if the standard deviation for C-reactive protein concentrations among arthritis patients was previously documented at 6 mg/dL, how many patients should be recruited for each group of individuals in the study, assuming a 95% confidence interval will be used to quantify the mean differences between the control group and the treatment group?
    A) n for the treatment group = 95 and n for the control group = 95
    B) n for the treatment group = 123 and n for the control group = 123
    C) n for the treatment group = 47 and n for the control group = 48
    D) n for the treatment group = 48 and n for the control group = 47

True/False

  1. True or False? To calculate the finalized n for a study, one should take the total number of participants needed to ensure the desired confidence interval and divide it by the proportion of individuals expected to be retained throughout the course of the study.
  2. True or False? A researcher wants to be sure the mean difference in the change in blood pressure has a margin of error no more than 5 points and the difference in the standard deviation between the mean blood pressure points from the first medication used to treat high blood pressure and the second medication used to treat high blood pressure is 14 points. The desired sample size required to ensure a 95% confidence interval for the proposed study used to compare the efficacy of two medications used to treat high blood pressure during a cross-over trial is n = 31.
  3. True or False? A researcher wants to estimate the impact prenatal care during pregnancy can have on premature deliveries by conducting a retrospective case-control study on new moms. If the prevalence of premature births is approximately 10.9%, the researcher should enroll a total of 586 women in the study if the researcher wants to construct a 90% confidence interval for the difference in proportions that has a margin of error of no more than 3%.
  4. True or False? It is not important for researchers to account for attrition or loss of participants during follow-up.
  5. True or False? The effect size is the difference in the parameter of interest that represents a clinically meaningful difference (in standard deviation units).

Chapter 09

Multiple Choice

  1. A specific medication used to prevent strokes, heart attacks, and blood clots requires a different dosage of medication for members of the African American population than the Caucasian population because a specific gene affects the way the drug is metabolized within the body. This is an example of which of the following?
    A) Confounding
    B) Selection bias
    C) Differential bias
    D) Effect modification
  2. A new and relatively expensive medication is released into the population to treat type II diabetes. A doctor notices that poor patients are less likely to see effects from the medication than more wealthy patients, but after conducting a survey the doctor finds the poor patients are less likely to fully comply with their medication regimen because they cannot afford to take the medication on a regular basis. This is an example of which of the following?
    A) Statistical interaction
    B) Confounding
    C) Selection bias
    D) Recall bias
  3. Research has found that circumcision has a protective effect and helps prevent HIV in men who have sex with women, but circumcision does not seem to have the same protective effect helping to prevent HIV in men who have sex with men. This is an example of which of the following?
    A) Confounding
    B) Selection bias
    C) Effect modification
    D) Recall bias
  4. A study is conducted in patients with HIV. The primary outcome is CD4 cell count, which is a measure of the stage of the disease. Lower CD4 counts are associated with more advanced disease. The investigators are interested in the association between vitamin and mineral supplements and CD4 count. A multiple regression analysis is performed relating CD4 count to use of supplements (coded as 1 = yes, 0 = no) and to duration of HIV, in years (i.e., the number of years between the diagnosis of HIV and the study date). For the analysis,
    Y ̂ = CD4 count. Y ̂= 501.41 + 12.67 Supplements – 30.23 Duration of HIV
    What is the expected CD4 count for a patient not taking supplements who has had HIV for 5 years?

A) 350.26
B) 67.82
C) 302.47
D) 1

  1. The data presented is a multiple logistic regression analysis and the models are shown below. In the models below, the data are coded as follows: p = the proportion of children with a diagnosis of ADHD, Child Exposed and Father’s Diagnosis are coded as 1 = yes and 0 = no. What is the odds ratio adjusted for father’s diagnosis? (Hint: Use only the appropriate model to find the odds ratio)
    (1) “ln” (p ̂/((1-p ̂)))= –2.216 + 1.480 Child exposed

(2) Father with diagnosis: “ln” (p ̂/((1-p ̂)))= –1.665 + 1.297 Child exposed

(3) Father without diagnosis: “ln” (p ̂/((1-p ̂)))= –2.343 + 0.823 Child exposed

(4) “ln” (p ̂/((1-p ̂)))= –2.398 + 1.501 Child exposed + 0.906 Father’s diagnosis

A) 4.49
B) 7
C) 2.88
D) 1.501

True/False

  1. True or False? An r value of –0.3 indicates a strong negative association.
  2. True or False? An r value of 0.5 indicates a positive moderate correlation.
  3. True or False? A linear regression equation and multiple linear regression equations can be used to calculate y if one is given the x values. However, a logistic regression equation cannot be used to calculate y when one is given x value.
  4. True or False? Multiple logistic regression analysis applies when there is a single dichotomous outcome and only one independent variable.
  5. True or False? Multivariable methods include a number of specific procedures to simultaneously assess the relationships between several exposure or risk factor variables and a single outcome.

Sample Solution

ACED ESSAYS