FA Flashcards
Clinical trial - definition
Experimental study involving humans. Compares therapeutic benefits of 2 or more treatments, or the treatment and placebo
Double blinded study
Neither patient nor doctor knows whether the patient is in the treatment or control group
Triple blind refers to
The additional blinding of the researchers analyzing data
Clinical trial study quality improves when study is
- Randomized
- Controlled
- Double blinded
Clinical trial phase 1 sample
Small number of healthy volunteers or patients with disease of interest
Clinical trial phase 1 purpose
Assesses
- safety (is it safe?)
- toxicity
- pharmacokinetics
- Pharmacodynamics
Clinical trial phase 2 sample
Small number of patients with disease of interest
Clinical trial phase 2 purpose
Assess treatment
- efficacy (does it work?)
- optimal dosing
- adverse effects
Clinical trial phase 3 sample
Large number of patients randomly assigned either to the treatment under investigation or the best available treatment (or placedo)
Clinical trial phase 3 purpose
Compares the new treatment to the current standard of care (is it as good or better?)
Clinical trial phase 4 sample
Postmarketing surveillance trial of patients after approval
Clinical trial phase 4 purpose
Detects rare or long term adverse effects. Can result in a drug withdrawn from market (can it stay?)
Types of studies
- Cross-sectional study
- Case-control study
- Cohort study
- Twin concordance
- Adoption study
Adoption study design
Compares sibling raised by biological vs adoptive parents
Adoption study measures
Heritability and influence of environmental factors
Twin concordance study measures
Heritability and influence of environmental factors (nature vs nurture)
Twin concordance study design
Compares frequency with which both monozygotes twins or both dizygotic twins develop same disease
Cross-sectional study type
Observational
Cross-sectional study design
Collects data from a group of people to assess frequency of disease and related factors at a particular point in time (disease PREVALENCE)
Cross-sectional study/ask
What is happening?
Case control study type
Observational and retrospective
Cross-sectional study measures
- Disease prevalence
2. Can show risk factor association with disease (but does not establish causality)
Case control study/asks
What happened
Case control study design
- Compares a group of people with disease to a group without disease
- Look for prior exposure or risk factors
Case control study measure
Odds ration (OR)
Case control study example (copd-smoking)
Patients with copd had higher odds of a history of smoking than those without copd
Cohort study type
Observational and prospective or retrospective
Cohort study design
- Compares a group with a given exposure of risk factor to a group without such exposure
- Looks to see if exposure increases the likehood of disease
- Can be prospective (who will develop the disease) or retrospective (historical) (who developed the disease)
Cohort study measure
Relative risk
Cohort study/ask
Who developed the disease
Or
Who will develop the disease (exposed vs not
Cohort study example (copd/smoker)
Smokers had a higher risk of developing copd than nonsmokers
Clinical treatment trials - type of study (why)
cohort study –> some members with a specific illness are given one treatment and other members are given another treatment or placebo
Fixed properties of a test
- Sensitivity
2. Specificity
Sensitivity - definition (and equation)
Proportion of all people with disease who test positive or,
The probability that a test detects disease when disease is present
TP/(TP+FN)=1-FN rate
High sensitivity test used for screening in disease with ….. prevalence
LOW
Specificity - definition (and equation)
Proportion of people without disease who test negative
or,
The probability that a test indicates non disease when disease is absent
TN/(TN+FP)=1-FP rate
100 sensitivity vs specificity - rule in vs rule out
sensitivity - rule out (low FN rate)
specificity - rule in (low FP rate)
Positive predictive value - definition (and equation)
- Proportion positive test that are true postive
- Probability that person actually has the disease given a positive test result
TP/(TP+FP)
PPV varies directly with
Prevalence or pretest probability
High pretest –> high PPV
Negative predictive value - definition (and equation)
- Proportion of negative test results that are true negative
- Probability that person actually is disease free given negative test result
TN/TN+FN
NPV varies inversely with
- Prevalence
- Pretest probability
High pretest probability –> low NPV
fixed properties of a test and properties that vary
fixed: specificity, sensitivity
vary: PPV, NPV (depending on disease prevalence)
association between PPV, NPV, sensitivity, specificity
high sensitivity –> high NPV
high specificity –> high PPV
Likelihood ratio?
likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that the same result would be excepted in a patient without the target disorder
positive likelihood ratios indicate
LR+ = sens / (1 - spec) = TP/FP –> probability of an individual with the condition having a positive test / probability of an individual without the condition having a positive test
negative likelihood ratios indicate
LR- = (1-sensit) / specif) FN/TN–> probability of an individual with the condition having a negative test / probability of an individual without the condition having a negative test
Number of LR in very useful diagnostic tests
LR+ grearer than 10
LR- lower than 0.1
how to estimate posttest odd
multiple LR with pretest odds
Prevalence
Number of existing cases/number of people at risk
At a point in time
Incidence rate
(Number of new cases in a specified time of period)/(population at risk during same time)
Prevalence directly reversible
- Incidence
2. Average disease dutation
Incidence and prevalence in common cold. Bigger?
Very similar because duration is short
Positive and negative predictive value vary depending on
Disease prevalence
town population is 7.500. In 2011, 200 residents diagnosed with RA. in 2012, 100 more residents are discovered by RA. incidence, prevalence?
incidence = 100/7300 prevelance = 300/7500
