P-values and confidence intervals Practice Questions

Question 1

A scientist in Chicago is studying a new blood test to detect Ab to EBV with increased sensitivity and specificity. So far, her best attempt at creating such an exam reached 82% sensitivity and 88% specificity. She is hoping to increase these numbers by at least 2 percent for each value. After several years of work, she believes that she has actually managed to reach a sensitivity and specificity much greater than what she had originally hoped for. She travels to China to begin testing her newest blood test. She finds 2,000 patients who are willing to participate in her study. Of the 2,000 patients, 1,200 of them are known to be infected with EBV. The scientist tests these 1,200 patients' blood and finds that only 120 of them tested negative with her new exam. Of the patients who are known to be EBV-free, only 20 of them tested positive. Given these results, which of the following correlates with the exam's specificity?

Accepted Answer

98%

Answer

82%

Answer

90%

Answer

84%

Answer

86%

Question 2

A randomized control double-blind study is conducted on the efficacy of 2 sulfonylureas. The study concluded that medication 1 was more efficacious in lowering fasting blood glucose than medication 2 (p ≤ 0.05; 95% CI: 14 [10-21]). Which of the following is true regarding a 95% confidence interval (CI)?

Accepted Answer

If the same study were repeated multiple times, approximately 95% of the calculated confidence intervals would contain the true population parameter.

Answer

The 95% confidence interval is the probability chosen by the researcher to be the threshold of statistical significance.

Answer

When a 95% CI for the estimated difference between groups contains the value ‘0’, the results are significant.

Answer

It represents the probability that chance would not produce the difference shown, 95% of the time.

Answer

The study is adequately powered at the 95% confidence interval.

Question 3

A surgeon is interested in studying how different surgical techniques impact the healing of tendon injuries. In particular, he will compare 3 different types of suture repairs biomechanically in order to determine the maximum load before failure of the tendon 2 weeks after repair. He collects data on maximum load for 90 different repaired tendons from an animal model. Thirty tendons were repaired using each of the different suture techniques. Which of the following statistical measures is most appropriate for analyzing the results of this study?

Accepted Answer

ANOVA

Answer

Chi-squared

Answer

Wilcoxon rank sum

Answer

Pearson r coefficient

Answer

Student t-test

Question 4

You are reading through a recent article that reports significant decreases in all-cause mortality for patients with malignant melanoma following treatment with a novel biological infusion. Which of the following choices refers to the probability that a study will find a statistically significant difference when one truly does exist?

Accepted Answer

Power

Answer

Type II error

Answer

Type I error

Answer

Confidence interval

Answer

p-value

Question 5

A medical research study is beginning to evaluate the positive predictive value of a novel blood test for non-Hodgkin’s lymphoma. The diagnostic arm contains 700 patients with NHL, of which 400 tested positive for the novel blood test. In the control arm, 700 age-matched control patients are enrolled and 0 are found positive for the novel test. What is the PPV of this test?

Accepted Answer

400 / (400 + 0)

Answer

700 / (700 + 300)

Answer

400 / (400 + 300)

Answer

700 / (700 + 0)

Answer

700 / (400 + 400)

Question 6

A study is being conducted on depression using the Patient Health questionnaire (PHQ-9) survey data embedded within a popular social media network with a response size of 500,000 participants. The sample population of this study is approximately normal. The mean PHQ-9 score is 14, and the standard deviation is 4. How many participants have scores greater than 22?

Accepted Answer

12,500

Answer

175,000

Answer

17,500

Answer

160,000

Answer

25,000

Question 7

A pharmaceutical corporation is developing a research study to evaluate a novel blood test to screen for breast cancer. They enrolled 800 patients in the study, half of which have breast cancer. The remaining enrolled patients are age-matched controls who do not have the disease. Of those in the diseased arm, 330 are found positive for the test. Of the patients in the control arm, only 30 are found positive. What is this test’s sensitivity?

Accepted Answer

330 / (330 + 70)

Answer

330 / (330 + 30)

Answer

370 / (30 + 370)

Answer

370 / (70 + 370)

Answer

330 / (400 + 400)

Question 8

You are currently employed as a clinical researcher working on clinical trials of a new drug to be used for the treatment of Parkinson's disease. Currently, you have already determined the safe clinical dose of the drug in a healthy patient. You are in the phase of drug development where the drug is studied in patients with the target disease to determine its efficacy. Which of the following phases is this new drug currently in?

Accepted Answer

Phase 2

Answer

Phase 4

Answer

Phase 1

Answer

Phase 0

Answer

Phase 3

Question 9

In a randomized controlled trial studying a new treatment, the primary endpoint (mortality) occurred in 14.4% of the treatment group and 16.7% of the control group. Which of the following represents the number of patients needed to treat to save one life, based on the primary endpoint?

Accepted Answer

1/(0.167 - 0.144)

Answer

1/(0.144 - 0.167)

Answer

1/(0.300 - 0.267)

Answer

1/(0.267 - 0.300)

Answer

1/(0.136 - 0.118)

Question 10

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

Accepted Answer

"Can you tell me more about the symptoms you have been experiencing?"

Answer

"Does the diarrhea typically precede the constipation, or vice-versa?"

Answer

"Is the diarrhea foul-smelling?"

Answer

"Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"

Answer

"Are the symptoms worse in the morning or at night?"

P-values and confidence intervals

Study Resources

Lessons

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Lessons

Definition and interpretation of p-values

Common misinterpretations of p-values

Confidence interval construction

Relationship between CIs and hypothesis testing

Multiple comparison problem

Correction methods (Bonferroni, FDR)

One-sided vs two-sided tests

Clinical vs statistical significance

Effect sizes and confidence intervals

Bayesian alternatives to p-values

Reporting standards in medical journals

P-value controversy and alternatives

Confidence intervals for non-parametric tests

Practice Questions

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