Biostats

Question 1

The probability that disease is present given a positive result

Answer 1

Positive predictive value

Question 2

The probability that disease is absent given a negative result

Answer 2

Negative predictive value

Question 3

A ratio representing the likelihood of having the disease given a positive result

Answer 3

Positive likelihood ratio

LR+ = Sensitivity ÷ (1 − Specificity)

Question 4

A ratio representing the likelihood of having the disease given a negative result

Answer 4

Negative likelihood ratio

LR− = (1 − Sensitivity)
÷ Specificity

Question 5

Correlation coefficient (r) values range from -1 to 1

The closer the r value is to its margins [-1, 1], the ______ the association.

Answer 5

stronger

• ie: if the correlation coefficient (r = -0.39) and is statistically significant (p = 0.005), the association is weak because its value is closer to 0 than to 1.

Question 6

_______ is a measure of effect used in survival analysis (or time-to-event analysis).
What is the null value?

Answer 6

Hazard Ratio

The null value for HRs is 1.00:

HR = 1.00 means that there is no difference in risk between the 2 groups.

HR <1.00 indicates a protective effect, whereas HR >1.00 indicates a detrimental effect.

Question 7

_________ of a medication is a measure of its possible BENEFIT minus its possible HARM.

Answer 7

net clinical benefit

For example, in patients with refractory or untreatable cancer, chemotherapy treatment leading to significant clinical improvement might result in a favorable NCB despite substantial toxicity of the medication.

Question 8

The basic premise of the ________ principle is that participants in trials should be analyzed in the groups to which they were randomized, regardless of whether they received or adhered to the allocated intervention and regardless of whether they withdrew from treatment.

Answer 8

intention-to-treat

holds that randomization is of paramount importance and that deviation from the original randomized groups can contaminate the treatment comparison.

Question 9

_____ quantifies the proportion of risk reduction attributable to a specific intervention or exposure as compared to a control

Answer 9

Relative risk reduction

RRR = (risk in unexposed − risk in exposed) / (risk in unexposed)

Question 10

The ____ usually indicates how high or low the risk for disease is among the exposed compared to the unexposed group.

Answer 10

Relative risk

RR = Risk of disease in exposed group / risk of disease in unexposed group

Question 11

The________ is a quantitative measure of inter-rater reliability (sometimes referred to as inter-rater concordance). It reflects the extent to which inter-rater agreement represents an improvement on chance agreement alone.

Answer 11

kappa statistic

Kappa values range from -1 (perfect disagreement) to +1 (perfect agreement), with kappa = 0 suggesting agreement due to chance

Question 12

The probability of a diseased person testing positive

- (probability of detecting the disease if it is present)

Answer 12

Sensitivity

Question 13

The probability of a nondiseased person testing negative

Answer 13

Specificity

Question 14

A ____ test can test the difference between 2 paired means; patients serve as their own control (eg, mean blood pressure before and after treatment in the same subjects).

Answer 14

paired t-test

Question 15

_____ test is best suited for a scenario where the mean values of a continuous variable in several groups (categorical variable) are being compared.

Answer 15

ANalysis Of VAriance (ANOVA)

Question 16

A funnel plot is helpful in assessing ______

Answer 16

publication bias
- 95% of studies should lie within the triangle centered on the summary estimate and extending 1.96 standard errors on either side

Question 17

________ occurs when the magnitude or direction of the effect of the independent variable on the dependent variable (outcome) varies depending on the level of a third variable.
- Separate (stratified) analyses should be conducted for each level of the effect modifier.

Answer 17

Effect modification

Question 18

attributable risk aka ______

Answer 18

risk difference

- measure of excess incidence of disease d/t a particular factor (ie: smoking)

Question 19

If the CI does not include the ______, that implies that the result was statistically significant

Answer 19

null value (ie: 0)

Question 20

Positive and negative predictive values are used to describe the clinical usefulness of a respective positive or negative test result.
However, they are not intrinsic characteristics of a test and can vary based on _______

Answer 20

disease prevalence in the tested population.

Question 21

True/False

Nonoverlapping confidence intervals ALWAYS imply a statistically significant difference between groups. However, the opposite is not necessarily true.

Answer 21

true

Question 22

There is an increased risk for type __ errors when multiple simultaneous hypotheses are tested at set p-values.

Interpretation of findings in clinical trials when multiple outcome measures are used without adjustment of the significance level may result in spurious findings and invalid conclusions.

Answer 22

Type I errors (ie, false positives)

Question 23

When hazard ratios or Odd ratios are included, statistically significant confidence intervals means __________

Answer 23

CI do not include the null value of 1.00 for HRs or 1/0 for OR

Question 24

________ refers to repeating primary analysis calculations after modifying certain criteria or variable ranges; the goal is to determine whether such modifications significantly affect the results initially obtained.

(ie: exclude high fluctuations in glucose lvls)

Answer 24

Sensitivity analysis

Question 25

Recall bias results from the inaccurate recall of past exposure by participants in a study. It applies mostly to case-control designs and leads to misclassification of _______

Answer 25

exposure.

Question 26

Nonoverlapping confidence intervals always imply a statistically significant difference between groups.
Is the opposite true?

Answer 26

No, not necessarily

Question 27

Positive likelihood ratio:

Negative likelihood ratio:

Answer 27

LR+ = sensitivity / (1 - specificity)

LR- = (1 - sensitivity) / specificity

Positive and negative likelihood ratios (like sensitivity and specificity) are independent of disease prevalence.

Question 28

overlapping SEM error bars suggest __________

Answer 28

a non-statistically significant difference

(not always true with other error bar types).

Question 29

A ________ study design (or fully crossed design) is a type of experimental study design that utilizes >2 interventions and all combinations of these interventions.

Answer 29

factorial

Question 30

The probability of type II errors (β) is related to the power of a study (calculated as 1 − β).

Answer 30

true