Primer 13 - Biostats, Studies And Diagnostic Tests.

Question 1

What is a retrospective study?

Answer 1

The investigators ask the experiments to look back into their past to see relevant information such as traveling, what they ate, etc. to triangulate a certain risk factor.

Question 2

What is a case-control study?

Answer 2

Retrospective, observational study with no intervention.

Question 3

What does a case-control study yield and what does it mean?

Answer 3

Odds ratio (OR): compares the odds that someone will develop the bad outcome in the exposed group to the odds that someone will develop that bad outcome without the exposure.

Question 4

What does a cohort study yield?

Answer 4

Relative risk or Risk ratio.

Question 5

What does a case-control study do?

Answer 5

It compares a group of people with the disease (case) to a group of people without the disease(control), to look for potential risk factors and exposures that can account for that bad outcome.

Question 6

How do you calculate risk ratio?

Answer 6

Divide the risk or rate of the disease in the exposed group by the risk or rate of the disease in the unexposed group.

Question 7

What is a cross-sectional study?

Answer 7

It is a observational study of a population at one point in time (how many people in the US have COPD at as of January 13 2013): AKA prevalence.

Question 8

What type of study can yield prevalence?

Answer 8

Cross-sectional study.

Question 9

What is a Twin concordance study?

Answer 9

An observational study that looks at heterozygous and homozygous twins and measures the heritability of diseases and traits.

Question 10

What is a clinical trial?

Answer 10

Experimental study, where the investigator intervenes to draw a conclusion. It uses human subjects.

Question 11

What is a controlled clinical trial?

Answer 11

An experimental group receives an experimental treatment and a controlled group that gets a placebo or a comparative drug that is well known.

Question 12

What is a randomized clinical trial and what does it avoid?

Answer 12

The participants are assigned to one group or another randomly. It avoids bias.

Question 13

What does double blinded study means?

Answer 13

The study design does not allow either the participant or the investigator to know wether that participant is receiving the experimental treatment or placebo.

Question 14

What is a Phase 1 trail for an experimental drug?

Answer 14

It looks to see if the experimental drug is safe: the drug is given to healthy subjects to see if the drug is safe and investigate the pharmacokinetics of it (how a healthy body handles the drug).

Question 15

What is a Phase 2 trail for an experimental drug?

Answer 15

Looks to see if the experimental drug works: Patients with a disease are given an experimental drug and see the efficacy, appropriate dosage and adverse effect.

Question 16

What is a Phase 3 trail for an experimental drug?

Answer 16

To see if the experimental drug works better: Is it better than a placebo or better than the established treatment?

Question 17

What is a Phase 4 trail for an experimental drug?

Answer 17

It is postmarketing surveillance: It looks for rare adverse effects and very long term effects once the experimental drug is on the market.

Question 18

What is a meta-analysis?

Answer 18

It combines data from many studies to give a better insight. It increases the statistical power, thereby reach statically better conclusions than in just individual studies.

Question 19

What are the x and y axis of a diagnostic test square?

Answer 19

On the Y axis is the Test (positive and negative) and the X axis is the Disease (positive and negative).

Question 20

What is a True Positive (TP) in a Diagnostic test?

Answer 20

People who test positive and how actually have the disease.

Question 21

What is a False Positive (FP) in a Diagnostic test?

Answer 21

People who Test positive but do not have the disease.

Question 22

What is a False Negative (FN) in a Diagnostic test?

Answer 22

People that have the disease but test negative for the disease.

Question 23

What is a True Negative (TN) in a Diagnostic test?

Answer 23

People that do not have the disease and are testing negative for the disease.

Question 24

How do we determine the sensitivity of a diagnostic test?

Answer 24

Sensitivity = True positive / (True positive + False negative).

Question 25

How do we determine specificity in a diagnostic test?

Answer 25

Specificity = True negative / (True negative + False negative).

Question 26

What is Positive predictive value (PPV) and is it calculated?

Answer 26

Positive Predictive value is the probability that subjects with a positive screening test truly have the disease.
PPV = True positive / (True positive + False positive).

Question 27

What is Negative predictive value (NPV) and is it calculated?

Answer 27

Negative predictive value is the probability that subjects with a negative screening test truly do not have the disease.
NVP: True negative / (False negative + True negative).

Question 28

What is the sensitivity, specificity, positive and negative predictive value using antibodies to X to detect disease X?
True positive: 800.
False positive: 200.
False Positive: 100.
False negative: 1400.

Answer 28

Sensitivity: 800/(800+100) = 0.889
Specificity: 1400/ (1400+ 200) = 0.875
PPV: 800/(800 + 200) = 0.8
NPV: 1400/(1400 + 100) = 0.933

Question 29

What changes the values of positive predictive value and negative predictive value?

Answer 29

Disease prevalence.

Question 30

A physician is looking for risk factors for pancreatitis. He interviews 100 hospitalized patients with pancreatitis and 100 hospitalized patients without pancreatitis. What type of study is this?

Answer 30

Case-control study.

Question 31

A group of smokers and a group of non-smokers are followed over 20 years. Every two years, it is determined who develops cancer and who does not. What type of study is this?

Answer 31

Cohort study; you started with an exposed population and looking for a specific outcome.

Question 32

A certain screening test has a 1% false-negative rate. What is the sensitivity of the test?

Answer 32

It is 99%; Sensitivity = 1 - false negative test.