Sample Questions from the Biostatistics Q-Bank


Sample Question 1

A group of investigators have designed a study to determine if ezetimibe (Zetia) was more effective than cholestyramine (Questran) for the treatment of hyperlipidemia. They designed the study so that 500 patients would be randomly assigned to one of 2 groups: ezetimibe 10 mg once daily or cholestyramine 4 g by mouth twice a day with meals. At baseline, patients had fasting lipid profile done. These patients were then prospectively followed for 6 months.  At the end of the study (6-months) the patients had a follow up visit where fasting lipid profiles completed. The primary endpoint was to determine the change in LDL-c (mg/dL) from baseline. The secondary endpoints included: 1-The proportion of patients developing cholestasis or needing a cholecysectomy.  Which of the following statistical tests would you recommend for answering the primary objective (assume sample or population studied is normally distributed)? 

     a.     Student's t-test
     b.     Paired t-test
     c.     Chi Square
     d.     ANOVA

Correct Answer = a

Rationale Provided:

The best way to figure this is to do the following:  First ask, "How many groups (or samples) does this study have?" = 2.  Second, "Are these two groups (or samples) related (i.e., same patient) or independent (i.e., not the same patients in both groups)? = Independent.  Third, now determine the endpoint, "What is the endpoint?" In this case, the investigators specifically want to know the change in LDL-c or the amount of lowering in the LDL-c in mg/dL.  This is a concentration and thus each mg/dL is the same in magnitude and thus considered to be continuous (note: the change can be to infinity, there is no ranking or scale here).

Thus, a study using 2 independent groups evaluating a continuous data variable (with normal distribution), the correct statistical test would be a Student's t-test.  A paired t-test would have been used if the two groups were related (not independent).  A chi-square is used for assessing nominal or categorical data (i.e., an endpoint that causes you to have answer a "yes" or "no" question.  An ANOVA is used when there are 2 or more independent groups being evaluated.

Sample Question 2

When calculating power, the reduction in Beta (β) will likely result in what type of change to the sample size needed? 

     a.     Increase
     b.     Decrease
     c.     No change
     d.     Beta is not used in the calculation of Power

Correct Answer = a

Rationale Provided:

Since Beta (β) by definition is the probability of a Type II error, then Power = 1-Beta is the probability of NOT making a Type II error. Note: the larger the Beta the lower the power of study and greater chance of making a Type II error.  Therefore, the smaller the Beta the larger the power and less chance of making a type II error, results in the study that needs more patients or larger sample size in order to find a difference if it in fact does exist.  Type II error occurs when a study states there is no difference between the groups assessed but in reality there is a difference.  Any time a study fails to find a statistical difference between two groups the greater the chance that a Type II error has occurred.

Sample Question 3

A patient is seen in the Emergency Center with an acute gastrointestinal bleed secondary to dabigatran (Pradaxa), a new drug that was approved by the FDA within the last 2 years. Where should this adverse event be reported?

  1. Centers for Disease Control
  2. MedWatch
  3. National Institutes of Health
  4. Hospital administrator

Correct answer:  b

Rationale provided: 

MedWatch is the FDA's safety information and adverse event reporting program where anyone can voluntarily report an adverse event that is suspected to be associated the use of an FDA-regulated drug, biologic, medical device, dietary supplement or cosmetic.  Centers for Disease Control is a United States federal agency whose purpose is to protect public health through health promotion, disease prevention, and preparation for new threats.  The National Institutes of Health is the medical research agency for the United States, funding much of the medical research in the world.  Hospital administrators are more focused on the global aspects of managing a health care and would delegate the responsibility of adverse reaction reporting to the hospital pharmacy director.

 

Sample Question 4

A patient is seen in the Emergency Center with an acute gastrointestinal bleed secondary to dabigatran (Pradaxa), a new drug that was approved by the FDA within the last 2 years. Where should this adverse event be reported?

      a.    Centers for Disease Control
      b.    MedWatch
      c.    National Institutes of Health
      d.    Hospital administrator

Correct Answer = b

Rationale provided: 

MedWatch is the FDA's safety information and adverse event reporting program where anyone can voluntarily report an adverse event that is suspected to be associated the use of an FDA-regulated drug, biologic, medical device, dietary supplement or cosmetic.  Centers for Disease Control is a United States federal agency whose purpose is to protect public health through health promotion, disease prevention, and preparation for new threats.  The National Institutes of Health is the medical research agency for the United States, funding much of the medical research in the world.  Hospital administrators are more focused on the global aspects of managing a health care and would delegate the responsibility of adverse reaction reporting to the hospital pharmacy director.