Biostatistics

Question 1

Sensitivity

Answer 1

Sensitivity is thought of as the probability that a symptom is present given that the person has the disease.

Sensitivity is the proportion of patients with the disease who have a positive test result.

Question 2

Specificity

Answer 2

Specificity can be thought of as the probability that the symptom is not present given that a person does not have a disease.

Specificity is the proportion of patients without the disease who have a negative test result.

Question 3

incidence

Answer 3

The incidence of a disease is the probability that a person with no prior disease will develop a new case of the disease over a specific time period.

Question 4

p value

Answer 4

The p value for any hypothesis test is the level at which we would be indifferent between accepting or rejecting the null hypothesis given the sample data at hand. It can also be thought of as the probability of obtaining a test statistic as extreme or more extreme than the actual test statistic obtained, given that the null hypothesis is true.

Question 5

Positive predictive value

Answer 5

Positive predictive value refers to the proportion of patients who have a positive test result who actually have the disease.

The positive predictive value increases with increasing disease prevalence

Question 6

Negative predictive value

Answer 6

Negative predictive value refers to the proportion of patients with a negative test result who truly do not have the disease.

Negative predictive value increases with lower disease prevalence.

Question 7

Likelihood ratio (LR)

Answer 7

likelihood ratio (LR) is a statistical indicator of how much the result of a diagnostic test will increase or decrease the pretest probability of a disease in a specific patient.

A clinical rule of thumb is that LR(+) values of 2, 5, and 10 correspond to an increase in disease probability by 15%, 30%, and 45%, respectively. With a pretest probability of 50%, a positive echocardiographic stress test would increase the likelihood of disease by approximately 45%, leading to a posttest probability in the range of 95%, which would be very useful clinically in making further treatment decisions.

Question 8

NNT

Answer 8

It is actually the reciprocal of absolute risk reduction.

ie: (1% − 2%) = 1% or 0.01

NNt = 1/.01 = 100