Terminology 08 06 2014 Flashcards
Specificity
Characteristic of a test:
Of the pole who don’t have the disease, how many of them will have a negative test.
Specificity = TN/ (TN + FP)
SP - IN
Sensitivity
Characteristic of a test:
How many people with the disease with have a positive test.
Sensitivity = TP/ (TP + FN)
SN- OUT
Predictive Value
probability of a disease given the results of a test.
Positive predictive value
probability of a disease in a patient with a (+) test (abnormal)
PV = number of people with the disease/ number of people who have a positive test
Negative predictive value
probability of not having the disease when the test value is negative.
= (# of ppl w/o disease that tested neg) divided by (# of people with negative test)
What is a likelihood ratio?
it expresses how many more times (or less times) likely a test result is to be found in diseased vs. non-diseased.
Positive likelihood ratio
= ratio of the proportion of diseased people with a + result
divided by
proportion of non-diseased with a positive result.
= (Sensitivity)/ (1- specificity)
Negative likelihood ration
= proportion of diseased people with a (-) test
divided by
proportion of non-diseased with (-) test
Risk Reduction
= ARR/ event rate
Event rate = (a/a+c)
accounts for the effectiveness of proposed treatment and relative likelihood of an incident occur in gin the absence of treatment.
case-control study
observational and retrospective
compares a group of people with disease to group without disease.
Looks for prior exposure or risk factor
measures odds ration (OR)
used to help look at rare diseases
Patient with disease is matched to a patient without disease
cohort study
observational, prospective, or retrospective
compares a group with a given exposure or risk factor to a group without that exposure.
Looks to see if exposure increases the likelihood of disease.
measures Relative risk: event rate of exposed/ event rate of non-exposed.
cross-sectional study
observational
Collects data from a group of people to asses frequency of disease at a particular point in time.
measures Disease prevalence – can show risk factor for association with disease BUT does not establish causality
Twin concordance study
compares frequency with which both monozygotic twins or both dizygotic twins develop the same disease.
Measures heritability
Adoption study
compares siblings raised by biological vs. adoptive parents.
Measures heritability and influence of environmental factors.
Clinical trials
phase 0–
pre-phase I: patients take a small dose of
drug to see if you are hitting targets of drug.
- drug needs to have a wide therapeutic
windows
- target must be known.
- amount of drug given do not have any
therapeutic value.
phase 1
Small number of healthy volunteers, people
with disease. Asses toxicity and
pharmacokinetics.
phase 2
Small number of patients w/disease
- asses efficacy and optimal dosing and
adverse effects.
phase 3
Large number of patients randomly assigned
either to the treatment under investigation or
the best available placebo.
-Compares new treatment.
phase 4
Post market survellience : detects rare or long term adverse effects
incidence
of NEW cases in a specific period of time/ population at risk during that same period.
prevalence
of existing cases/ population at risk.
odds ratio
used in Case-control studies
odds that a group with the disease was exposed to a risk factor/ odds that group without disease was exposed
(TP)(TN)/ (FP)(FN)
relative risk
Cohort studies
Risk of developing disease in exposed group/ risk in unexposed group.
a/(a+c) / c/ (c+d)
attributed risk
the difference in risk between exposed and unexposed groups.
number needed to treat
number of patients who need to be treated to prevent 1 bad outcome.
number needed to harm
number of patients who need to be exposed to a risk factor for 1 patient to be harmed.
selection bias
nonrandom assignment to participation in a study group
recall bias
knowledge of presence of disorder alters recall by subjects
- common in retrospective studies
sampling bias
subjects are not representative of vernal population.
- results cannot be generalized to the public.
- a type of selection bias
late-look bias
information gathered at an inappropriate time.
- ex. using a survey to study a fatal disease
- only patients who are still alive can answer
procedure bias
subjects in different groups are not treated the same.
- more attention is paid to treatment group
confounding bias
when a factor is related to both exposure and outcome BUT is not in the causal pathway.
-factor distorts or confuses effect of exposure on outcome.
lead-time bias
early detection confused with an increase in survival
observer-expectancy effect
occurs when a researcher’s believe in the efficacy of a treatment changes the outcome of that treatment.
Hawthorne effect
group being studied changes its behavior owing to the knowledge of being studied
Meta-analysis
pools data and integrates result from several similar studies to reach an overall conclusion and increase statistical power.
Limited by qua lit of individual studies or bias in study selection.
