Flashcards in Primer 13 - Biostats, Studies And Diagnostic Tests. Deck (32):
What is a retrospective study?
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.
What is a case-control study?
Retrospective, observational study with no intervention.
What does a case-control study yield and what does it mean?
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.
What does a cohort study yield?
Relative risk or Risk ratio.
What does a case-control study do?
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.
How do you calculate risk ratio?
Divide the risk or rate of the disease in the exposed group by the risk or rate of the disease in the unexposed group.
What is a cross-sectional study?
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.
What type of study can yield prevalence?
What is a Twin concordance study?
An observational study that looks at heterozygous and homozygous twins and measures the heritability of diseases and traits.
What is a clinical trial?
Experimental study, where the investigator intervenes to draw a conclusion. It uses human subjects.
What is a controlled clinical trial?
An experimental group receives an experimental treatment and a controlled group that gets a placebo or a comparative drug that is well known.
What is a randomized clinical trial and what does it avoid?
The participants are assigned to one group or another randomly. It avoids bias.
What does double blinded study means?
The study design does not allow either the participant or the investigator to know wether that participant is receiving the experimental treatment or placebo.
What is a Phase 1 trail for an experimental drug?
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).
What is a Phase 2 trail for an experimental drug?
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.
What is a Phase 3 trail for an experimental drug?
To see if the experimental drug works better: Is it better than a placebo or better than the established treatment?
What is a Phase 4 trail for an experimental drug?
It is postmarketing surveillance: It looks for rare adverse effects and very long term effects once the experimental drug is on the market.
What is a meta-analysis?
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.
What are the x and y axis of a diagnostic test square?
On the Y axis is the Test (positive and negative) and the X axis is the Disease (positive and negative).
What is a True Positive (TP) in a Diagnostic test?
People who test positive and how actually have the disease.
What is a False Positive (FP) in a Diagnostic test?
People who Test positive but do not have the disease.
What is a False Negative (FN) in a Diagnostic test?
People that have the disease but test negative for the disease.
What is a True Negative (TN) in a Diagnostic test?
People that do not have the disease and are testing negative for the disease.
How do we determine the sensitivity of a diagnostic test?
Sensitivity = True positive / (True positive + False negative).
How do we determine specificity in a diagnostic test?
Specificity = True negative / (True negative + False negative).
What is Positive predictive value (PPV) and is it calculated?
Positive Predictive value is the probability that subjects with a positive screening test truly have the disease.
PPV = True positive / (True positive + False positive).
What is Negative predictive value (NPV) and is it calculated?
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).
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.
Sensitivity: 800/(800+100) = 0.889
Specificity: 1400/ (1400+ 200) = 0.875
PPV: 800/(800 + 200) = 0.8
NPV: 1400/(1400 + 100) = 0.933
What changes the values of positive predictive value and negative predictive value?
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?
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?
Cohort study; you started with an exposed population and looking for a specific outcome.