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Flashcards in Statistics and Ethics Exam Questions Deck (20):
1

The results of a study undertaken to determine the utility of urinary leukocyte dipstick testing in the diagnosis of urinary tract infections (UTI) in febrile children is shown below.

Number with UTI  Number without UTI
Leukocyte test positive   70    10
Leukocyte test negative   30    90

In this study, the negative predictive value of the leukocyte dipstick test is:
A. 35%
B. 70%
C. 75%
D. 90%
E. 95%

Answer C. 75%

NPV = d/c+d = 90/120 = 75%
(test outcome negative/true negative)

2

The following results were obtained from a randomised controlled trial of a new artificial surfactant
called "S".

 

The number of babies that you would need to treat with “S” to prevent one case of chronic lung
disease is:
A. 5
B. 10
C. 15
D. 20
E. 30
 

Answer B. 10

NNT= 1/ARR
ARR=CER-EER
CER= CE/CS
EER=EE/ES

so NNT = 1/CER-EER
1/ 0.8-0.7 = 10

NNT= number needed to treat
ARR = absolute risk reduction
CER = control event rate
EER = experiment event rate
CE = control event
EE = experiment event
CS = control subjects (sum of)
ES = event subjects (sum of)

3

A new screening test is developed for Condition X. It is trialled in a population of 1100 children, of whom 100 have Condition X and the remainder do not. Of the 200 children who screen positive, 50 have Condition X.  
What is the specificity of the screening test?

A. 0.15.
B. 0.25.
C. 0.50.
D. 0.85.
E. 0.94

Answer D. 0.85

Sn = a/a+c
Sp = d/b+d

4

The major objective of a phase III clinical trial is to determine which one of the following?

A. Cost effectiveness.
B. Efficacy of an experimental therapy. 
C. Efficacy of a standard therapy. 
D. Maximum tolerated dose. 
E. Toxicity profile. 

Answer B. Efficacy of an experimental therapy

Phase I Clinical Trial

Phase I clinical trials are done to test a new biomedical intervention for the first time in a small group of people (e.g. 20-80) to evaluate safety (e.g. determine a safe dosage range and identify side effects).

Phase II Clinical Trial

Phase II clinical trials are done to study an intervention in a larger group of people (several hundred) to determine efficacy (whether it works as intended) and to further evaluate its safety.

Phase III Clinical Trial

Phase III studies are done to study the efficacy of an intervention in large groups of trial participants (from several hundred to several thousand) by comparing the intervention to other standard or experimental interventions (or to non-interventional standard care) as well as to monitor adverse effects and to collect information that will allow the intervention to be used safely.

Phase IV Clinical Trial

Phase IV studies are done after an intervention has been marketed. These studies are designed to monitor the effectiveness of the approved intervention in the general population and to collect information about any adverse effects associated with widespread use over longer periods of time.

Other Clinical Trials

Researchers may also conduct exploratory studies, sometimes referred to as ‘Phase 0 trials’ or ‘pilot studies’ that come before Phase I trials and are used to test how the body responds to an experimental drug.  In these studies, small doses of the new drug are given once or for a short time to a very limited number of people.

5

A test has a sensitivity of 95% and a specificity of 90%.  It is used to screen the general population for a condition that has a prevalence of 1 in 100,000. 

What will the positive predictive value be nearest to?

A. 0.01%.
B. 0.05%.
C. 0.1%.
D. 0.5%.
E. 1%.

6

The major objective of a phase III clinical trial is to determine which one of the following?

A. Cost effectiveness.
B. Efficacy of an experimental therapy.
C. Efficacy of a standard therapy.
D. Maximum tolerated dose.
E. Toxicity profile. 

Answer B. Efficacy of an experimental therapy

Phase I Clinical Trial

Phase I clinical trials are done to test a new biomedical intervention for the first time in a small group of people (e.g. 20-80) to evaluate safety (e.g. determine a safe dosage range and identify side effects).

Phase II Clinical Trial

Phase II clinical trials are done to study an intervention in a larger group of people (several hundred) to determine efficacy (whether it works as intended) and to further evaluate its safety.

Phase III Clinical Trial

Phase III studies are done to study the efficacy of an intervention in large groups of trial participants (from several hundred to several thousand) by comparing the intervention to other standard or experimental interventions (or to non-interventional standard care) as well as to monitor adverse effects and to collect information that will allow the intervention to be used safely.

Phase IV Clinical Trial

Phase IV studies are done after an intervention has been marketed. These studies are designed to monitor the effectiveness of the approved intervention in the general population and to collect information about any adverse effects associated with widespread use over longer periods of time.

Other Clinical Trials

Researchers may also conduct exploratory studies, sometimes referred to as ‘Phase 0 trials’ or ‘pilot studies’ that come before Phase I trials and are used to test how the body responds to an experimental drug.  In these studies, small doses of the new drug are given once or for a short time to a very limited number of people.

7

The parents of a child in the Intensive Care unit with a terminal illness make a choice not to pursue further treatment for their child's condition. Medical advice has been that there is little hope that any intervention would prolong the child's life. In this situation, which of the following should not be withheld?

A. Adequate sedation and analgesia.
B. Antibiotics.
C. Artificial hydration and nutrition.
D. Ionotrophic medications.
E. Red Cell transfusion. 

Answer A. Adequate sedation and analgesia.

8

The following table shows the results of the primary endpoint of a study of a new treatment for asthma, “Micoffstop”. Patients were recruited in a tertiary referral hospital after Intensive Care Unit admission.

If the same treatment and endpoint was used in a trial in a group of patients with non-ICU hospital admission for asthma, which of these measures of treatment effect is most likely to remain approximately the same?

A. Absolute risk reduction.
B. Cost-benefit analysis.
C. Number needed to treat.
D. Relative risk reduction.
E. Risk-benefit analysis.

9

You admit an eight-year-old girl to the Intensive Care Unit with septic shock. A randomised controlled trial recently showed that a new drug reduces mortality. In the study, 33 of 110 control patients (30%) died, compared to 30 of 120 (25%) in the treatment group. It costs $2,000 per treatment course. In order to save one life using this new drug, about how much would your hospital have to spend?

A. $2,500
B. $40,000
C. $50,000
D. $60,000
E. $66,000

Answer B. $40,000

NNT = 1/ARR

ARR = CER- EER

CER = 30% (30/100)

EER = 25% (25/100)

ARR = 30/100 - 25/100 = 5/100

NNT = 1/5/100 = 100/5 = 20

Each treatment costs $2000 so NNT x $2000 = $40,000

10

A test has a sensitivity of 95% and a specificity of 90%. It is used to screen the general population for a condition that has a prevalence of 1 in 100,000.
What will the positive predictive value be nearest to?

A. 0.01%.
B. 0.05%.
C. 0.1%.
D. 0.5%.
E. 1%.

11

The principle of informed consent relates to which ethical standard?

A. Autonomy.
B. Beneficence.
C. Justice.
D. Non-maleficence.
E. Privacy.

Answer A. Autonomy

  • Autonomy - Patients right to choose or refuse treatment
  • Beneficence - Taking actions that serve the best interests of the patient
  • Justice - fairness and equality of treatment
  • Non-maleficence - First, do no harm

 

12

Serum IgA antigliadin antibody testing is used to screen for coeliac disease in 1000 otherwise healthy relatives of patients with the condition. The test results are shown below.

The positive predictive value of the test is calculated as:

A. 120 / 880 = 14%.
B. 160 / 1000 = 16%.
C. 100 / 160 = 63%.
D. 120 / 160 = 75%.
E. 100 / 120 = 83%. 

Answer C. 100/160
PPV = a/a+b

13

Which one of the following steps in the design of a clinical trial of a new therapeutic agent most reduces the chance of a type II error?

A. Blinded assessment of outcomes.
B. Intention to treat analysis.
C. Random allocation.
D. Sample size calculation.
E. Stratification of major risk factors. 

Answer D. Sample size calculation.

Increasing sample size reduces the number of false negatives.

Type I Error - False positive

Type II Error - False negative

14

The impact of an intervention in clinical trials and in systematic reviews can be expressed in a number of ways.  One increasingly used format is the number needed to treat (NNT) which indicates how many patients have to be treated with the intervention of interest compared to the control intervention in order to achieve one successful outcome. 

In a systematic review of optimal home-management for asthma, the intervention was found to produce a 50% reduction in hospitalisation for asthma.  Approximately 10% of patients in the control group required hospitalisation compared to approximately 5% of those who received optimal home-management.

Which one of the following is the best estimate of the NNT for this intervention?

A. 2.
B. 5.
C. 10.
D. 20.
E. 50.

Answer D. 20

NNT = 1/ARR
ARR = CER-EER
CER = 10% (=10/100)
EER = 5% (=5/100)

ARR = 10/100 - 5/100
= 5/100 = 1/20
NNT = 1/ARR = 1/1/20 = 20/1 =20

15

From around what age can most children demonstrate a capacity to comprehend and offer an informed assent to medical procedures and medications that involve potentially lethal side effects?

A. 7-8 years.
B.  9-10 years.
C. 11-12 years.
D. 13-14 years.
E. 15-16 years. 

Answer C. 11-12 years

16

To minimise the risk of human immunodeficiency virus (HIV) transmission by blood transfusion, which of the following is the most important property of a blood screening test?

A. Accuracy.
B. Positive likelihood ratio.
C. Positive predictive value.
D. Sensitivity.
E. Specificity. 

Answer D. Sensitivity

"A negative test rules it out"

17

A disease has an annual incidence of 15 cases per 100,000.  The mean survival after diagnosis is five years.

What is the best estimate of the prevalence of this disorder?

A. 3 per 100,000.
B. 15 per 100,000.
C. 30 per 100,000.
D. 45 per 100,000.
E. 75 per 100,000.

Answer E. 75 per 100,000

15 cases per year, so including current year and previous four years, 75 current cases out of 100,000.

18

The need for informed consent before enrolling a patient in a clinical trial investigating a novel treatment is primarily based on the principle of:
A. autonomy.
B. beneficence.
C. justice.
D. nonmaleficence.
E. risk management. 

Answer A. autonomy.

19

Which one of the following steps in the design of a clinical trial of a new therapeutic agent most reduces the chance of a type II error?

A. Blinded assessment of outcomes.
B. Intention to treat analysis.
C. Random allocation.
D. Sample size calculation.
E. Stratification of major risk factors. 

Answer D. Sample size calculation.

Increasing sample size decreases type II (false negative) errors.

20

A new diagnostic test for a certain disease has been evaluated. Compared with the definitive diagnostic standard, this test has a sensitivity of 100% and a specificity of 95%. The prevalence of the disorder in the population to be tested is 0.1%.

What is the best estimate of the positive predictive value of the new test?
A. <1%.
B. 2%.
C. 5%.
D. 10%.
E. 25%.

Answer B. 2%

Prevalence is 0.1%, ie. 0.1 in 100, or 1 in 1000.

To use the percentages given (sensitivity 100%), a=100, c=0, b = 5000 and d = 95000 to make a total of 100000 subjects. 

a/a+b = 100/5100 = 1/51 = (1/50 to make calculation easier) = .02

To make this a percentage, multiply by 100 = 2%