Epidemiology and Biostatistics

Question 1

What is the design of a cross-sectional study?

What are the measures generated/used?

Answer 1

Studies the frequency of disease and frequency of related factors.

Measures disease prevalence and can show risk factor associated but not causation.

Question 2

What is the design of a case-control study?

What is the main measure it generates?

Answer 2

Compares a group of people with a disease to a group without the disease.

Studies if odds of prior exposure or RF differs by disease state.

Uses Odds Ratio.

Question 3

What is the design of a cohort study?

What is the main measure it generates?

Answer 3

Compares a group of people with a given exposure or RF to a group of people without such exposure.

Studies whether the exposure if associated with later development of the disease.

Measures the Relative Risk.

Question 4

What are the 4 phases of a drug trial?

Answer 4

(got to see if a drug can SWIM)

1. Is the drug Safe?
2. Does the drug Work?
3. Is there any Improvement?
4. Can it stay in the Market?

Question 5

What is the “Sensitivity” of a test?

How is it calculated?

Answer 5

Question 6

What is the “Specificity” of a test?

How is it calculated?

Answer 6

Question 7

What is the Positive Predictive Value?

How is it calculated?

Answer 7

Question 8

What is the Negative Predictive Value?

How is it calculated?

Answer 8

Question 9

Describe the effect on NPV and PPV of raising or lowering a cut-off point of a test result.

Answer 9

The test result can be positive between A-B.

Lowering the cut-off increases FP and reduces FN

Increasing the cut-off increases FN and reduces FP

Question 10

How is the positive likelihood ratio calculated?

How is the negative likelihood ratio calculated?

Answer 10

Question 11

Define an odds ratio:

How is it calculated using the classic 2x2 table?

Answer 11

Typically used in case-control studies.

An odds ratio depicts the odds of an event occuring given certain exposure versus the odds of the event occuring in the absence of that exposure.

OR = a/b ÷ c/d

OR = ad/bc

Question 12

Define relative risk:

How is it calculated?

Answer 12

RR is typically used in cohort studies.

It demonstrates the risk of developing disease in the exposed group divided by the risk of developing the disease in the control group.

RR = a/(a+b) ÷ c/(c+d)

Question 13

When are OR and RR similar?

Answer 13

When the prevalence is low; i.e for rare diseases.

Question 14

What is attributable risk?

How is calculated?

Answer 14

Attributable risk is the difference in risk between exposed on unexposed groups.

AR = a/(a+b) - c/(c+d)

Question 15

What is relative risk reduction?

How is it calculated?

Answer 15

The proportion of risk reduction attributable to the intervention as compared to a control.

RRR = 1 - RR

Question 16

Define absolute risk reduction:

How is it calculated?

Answer 16

The difference in risk (not the proportion) attributable to the intervention as compared to a control.

ARR = c/(c+d) - a/(a+b)

Question 17

What is number needed to treat?

How is it calculated?

Answer 17

The number of patients who need to be treated for one patient to benefit.

NNT = 1 / ARR

Question 18

What is number need to harm?

How is it calculated?

Answer 18

NNH is the number of patients who need to exposed to a risk factor for one patient to be harmed.

NNH = 1 / AR

Question 19

How does standard deviation help interpretation of normally distributed data?

Answer 19

Question 20

How is Standard Error calculated?

What does it represent?

Answer 20

SE = SD / √sample size

Lower values of the standard error of the mean indicate more precise estimates of the population mean. Usually, a larger standard deviation will result in a larger standard error of the mean and a less precise estimate.

Question 21

How do non-normal positive and negative skew distribution affect mean, mode, and median?

Answer 21

Question 22

What is a Type I error?

Answer 22

Stating that there is an effect or difference when none exists.

The null hypothesis is incorrectly rejected.

Question 23

What is Type II error?

Answer 23

Stating that there is not an effect or difference when one exists.

The null hypothesis is not rejected when it is in fact false.

Question 24

How can power be increased and ß be reduced?

Answer 24

Increase sample size

Increase the expected size effect

Increase the precision of measurement.

Question 25

What is a t-test used for?

Give an example.

Answer 25

(Tea is meant for 2)

Checks the difference between means of two groups.

E.g. comparing the mean BP between men and women.

Question 26

What is ANOVA?

Give an example of what ANOVA might be used for.

Answer 26

Analysis of Variance checks the differences between means of 3 or more groups.

E.g. comparing the mean BP between members of multiple ethnic groups.

Question 27

What is the Chi-square test used for?

Give an example.

Answer 27

Checks differences between 2 or more percentages or proportions of categorical outcomes.

E.g. comparing the percentage of members of 3 different ethnic groups who have essential hypertension.

Question 28

Why is it inappropriate to use the t-test or ANOVA on categorical variables?

Answer 28

The central tendency of categorical variables is given by its mode, since median and mean can only be computed on numerical data. Therefore, it does not follow a normal bell-curve distribution, and cannot be analyzed with tests that rely on a normal distribution such as the t-test or ANOVA.

Question 29

What is the Pearson correlation coefficient?

Answer 29

It is a measure of the linear correlation between two variables.

The closer the value is to 1, the stronger the linear correlation between the two variables.

Question 30

Compare Health Maintenance Organisation, Point of Service, Preferred Provider, and Exclusive Provider medical insurance plans with regard to restrictions on network, PCP, and referral system.

Answer 30