Behavioral Science - First Aid Flashcards
Cross-sectional study (observational) design
collects data from a group of people to assess frequency of disease at a particular point in time
(asks what is happening)
Measures of a cross-sectional study
- disease prevalence
- can show risk factor association with disease, but does not establish causality
Case-control study (observational/retrospective) design
compares a group of people with disease to a group without disease; looks for prior exposure or risk factor
(asks what happened)
Measures of a case-control study
-odds ratio
Cohort study (observational/prospective or retrospective) design
compares a group with a given exporsure or risk factor to a group without such exposure; looks to see if exposure increases the likelihood of disease
(prospective - asks who will develop disease)
(retrospective - asks who has developed the disease)
Meausres of a cohort study
-relative risk
Twin concordance study design
compares the frequency with which both monozygotic twins or both dizygotic twins develop the same disease
Meausres of a twin concordance study
heritability and influence of environmental factors
Adoption study design
compares siblings raised by biological vs adoptive parents
Measures of an adoption study
heritability and influence of environmental factors
A clinical trial is an experimental study involving humans that compares…
the therapeutic benefits of 2 or more treatments, or of treatment and placebo.
Study quality of a clinical trial is improved when the study is…
randomized, controlled and double-blinded.
Triple-blind refers to the…
additional blinding ofo the researchers analyzing the data.
Phase I Trial
- small number of healthy volunteers
- “Is it safe?”
- Assesses safety, toxicity and pharmacokinetics
Phase II Trial
- small number of patients with disease of interest
- “does it work?”
- Assesses treatment efficacy, optimal dosing, and adverse effects.
Phase III Trial
- large number of pts randomly assigned either to the treatment under investigationor to the best available treatment/placebo
- asks “is it as good or better?”
- compares new treatment to current standard of care
Phase IV Trial
- posmarketing surveillance trial of pts after approval
- “can it stay?”
- detects rare or long term effects
Sensitivity is the…
proportion of all people with a disease who test positive or the probability that a test detects disease when it is present. (true-positive rate)
A sensitivity value approaching 100% is desirable for…
ruling out disease and indicates a low-false negative rate.
High sensitivity tests should be used for screening in diseases with..
low prevalence.
Sensitivity =
TP/(TP +FN)
Specificity is the…
proportion of all people without disease who test negative or the probability that a test indicates non-disease when disease is absent. (true-negative rate)
Specificity value approaching 100% is desirable for…
ruling in disease and indicates a low false-positive rate.
High specificity tests should be used for…
confirmation after a positive screening test.
Specificity =
TN/(TN + FP)
Positive Predictive Value (PPV) is the…
proportion of positive test results that are true positive. The probability that a person actually has the disease given a positive test result.
PPV =
TP/(TP + FP)
PPV varies…
directly with prevalence or pretest probability. A high pretest probability leads to a high PPV.
Negative Predictive Value (NPV) is the…
proportion of negative test results that are true negative. The probability that a person is actually disease free given a negative test result.
NPV =
TN/(FN + TN)
NPV varies…
inversely with prevalence or pretest probability. A high pretest probability give a low NPV.
Incidence =
(number of new cases in a specified time period)/(population at risk during the same time period)
Prevalence =
(number of existing cases)/(population at risk)
Prevalence is about equal to…
the incidence rate x avg disease duration.
Prevalence is greater than incidence for…
chronic diseases.
The odds ratio is the…
odds that the group with the disease was exposed to a risk factor (a/c) divided by the odds that the group without disease was exposed (b/d).
Odds Ratio (OR) =
ad/bc
Relative risk is the risk of…
developing disease in the exposed group divided by the risk in the unexposed group.
If prevalence is low, the RR is about equal to…
the OR.
Relative Risk (RR) =
[a/(a+b)]/[c/(c+d)]
Relative risk reduction is the…
proportion of risk reduction attributable ot the intervention as compared to a control. RRR = 1 - RR
Attributable risk is the…
difference in risk between exposed and unexposed groups or the proportion of disease occurences that are attributable to the exposure.
Attributable risk =
[a/(a+b)] - [c/(c+d)]
Absolute risk reduction (ARR) is the…
difference in risk attributable to the intervention as compared to a control.
The number needed to treat is the…
number of pts who need to be treated for 1 pt to benefit. Calculated as 1/ARR.
Number needed to harm is the…
number of pts who need to be exposed to a risk factor for 1 pt to be harmed. Calculated as 1/AR.
Precision is the…
consistency and reproducibility of a test (reliability). The absence of random variation.
Increased precision decreases…
the standard deviation.
Accuracy is the…
trueness of test measurements (validity). The absence of systematic error or bias.
Selection bias is…
nonrandom assignment to participat in a sudy group. Most commonly a sampling bias.
Examples of Selection bias include:
- Berson bias (a study looking only at inpatients)
- Loss to follow-up (studying a disease with early mortality)
- Healthy worker and volunteer bias (study populations are healthier than the general population)
Strategies to reduce selection bias
- randomization
- ensure the choice of the rigth comparison group
Recall bias is…
awareness of disorder alters recall by subjects; common in retrospective studyies.
(ex. pts with disease recall exposure after learning of similar cases)
Strategy to decrease recall bias
decrease time from exposure to follow-up
Measurement bias is…
information is gathered in a way that distorts it.
Ex. Hawthorne effect - groups who know they’re being studied behave differently than they would otherwise
Strategy to decrease measurement bias
use of placebo control groups with blinding to reduce influence of participants and researchers on experimental procedures and interpretation of outcomes
Procedure bias is when…
subjects in different groups are not treated the same.
Ex. pts in treatment group spend more time in highly specialized hospital units
Observer-expectancy bias
researcher’s belief in the efficacy of a treatment changes the outcome of that treatment
(ex. if an observer expects the treatment group to show signs of recovery, then he is more likely to document positive outcomes)
Confounding bias is when…
a factor is related to both the exposure and outcome but not on the causal pathway and this leads to the factor distorting or confusin gthe effect of exposure on outcome.
Ex. of Confounding bias
Pulmonary disease is more common in coal workers than the general population; however, people who work in coal mines also smoke more frequently than the general population.
Strategies to reduce confounding bias
- multiple/repeated studies
- crossover studies (subjects act as their own control)-matching (pts with similar characteristics in both treatment and control groups)
Lead-time bias is when…
early detection is confused with increased survival; seen with improved screeing techniques
Ex. early detection makes it seem as though survival has increased, but the natural history of the disease has not changed.
Strategies to reduce lead-time bias
-measure “back-end” survival (adjust survival according to the serverity of the disease at the time of diagnosis)
Mean =
(sum of values)/(total number of values)