Biostatistics Flashcards
How is a cross-sectional study performed?
What information can be derived from it?
An observational study that collects data from a group of people at a single point in time.
Used to assess disease frequency and associated risk factors.
Measures disease prevalence and show risk factor association with disease - no causality. “What is happening?”
How is a case-control study performed?
What information can be derived from it?
What statistic is used to compare the groups?
An observational and retrospective design.
Compares a group of people with disease to a group without disease. Then, looks for prior exposure or risk factor.
Uses an odds ratio
“What happened?”
How is a cohort study performed?
What information can be derived from it?
What statistic is used to compare the groups?
An observational and prospective or retrospective design.
Compares a group with a given exposure or risk factor to a group without exposure. Does the exposure increase likelihood of disease?
Use relative risk
How is a twin concordance study performed?
What information can be derived from it?
Compares frequency with which both monozygotic twins or both dizygotic twins develop same disease. Measures heritability and influence of environmental factors.
How is an adoption study performed?
What information can be derived from it?
Compares siblings raised by biological versus adoptive parents with respect to disease. Measures heritability and environmental factors.
What is the purpose and typical study sample for a Phase I clinical trial?
Phase 1: “Is it safe?” Assess safety, toxicity, and pharmocokinetics.
Study sample is small number of healthy volunteers.
What is the purpose and typical study sample for a Phase II clinical trial?
“Does it work?” Assess treatment efficacy, optimal dosing, and adverse effects.
Study sample is a small number of patients with disease of interest.
What is the purpose and typical study sample for a Phase III clinical trial?
“Is it as good or better?” Compare the new treatment to the current standard of care.
Study sample is a large number of patients randomly assigned to either treatment under investigation or best available treatment (or placebo if none exists).
What is the purpose and typical study sample for a Phase IV clinical trial?
“Can it stay?” Detects rare or long-term adverse effects of treatment. Can result in removal from market.
Study sample: Postmarketing surveillance trial of patients after approval.
Below is a 2x2 table obtained from data gathered during a diagnostic test evaluation study.
What does each individual letter represent?
What about each horizontal and vertical sum?
A = True positive
B = False positive
C = False negative
D = True negative.
A+B = Total positive tests
C+D = Total negative tests
A+C = Total amount of people with disease
B+D = Total amount of people without disease
What does sensitivity measure?
Proportion of all people with disease who test positive, or the probability that a test detects disease when disease is present.
AKA the true positive rate.
How do you calculate sensitivity?
Sensitivity = TP / (TP + FN)
Where TP = true positive. FN = false negative.
On a typical 2x2 plot, this is A / (A+C)
OR
Sensitivity = 1 - false negative rate
What is a highly sensitive test useful for?
SN-N-OUT - A highly SeNsitive test, when Negative, rules OUT disease.
A highly sensitive test indicates a low false negative rate.
Used for screening in diseases with low prevalence.
What does specificity measure?
Specificity is the proportion of all people without disease who test negative, or the probability that a test indicates non-disease when a disease is absent.
AKA true negative rate.
How do you calculate specificity?
Specificity = TN / (TN + FP)
In a 2x2 plot of test versus disease, this = D / (D+B)
OR
Specificity = 1 - false-positive rate
What is an Odds ratio? How is it calculated?
When is it used?
Used in case-control studies.
Odds that the group with the disease (cases) was exposed to a risk factor (a/c) divided by the odds that the group without the disease (controls) was exposed (b/d)
OR = (a/c) / (b/d)
or
OR = AD/BC
