Term
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Definition
◦A third factor is either positively or negatively associated with both the exposure and outcome
Important Associations
1.Hidden factors affect result
2.unacceptability bias
Solution
1.multiple studies
2.good research design
3.meta-analysis
◦Confounders are not in the causal pathway ◾if not adjusted for can distort true association
◾either towards or away from the null hypothesis |
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Term
| •Selection bias or (sampling bias) |
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Definition
Nonrandom selection of study participants leads to erroneous conclusions ◾e.g. if investigating the adverse events associated with a new drug, those with either the best or worst outcomes may be more likely to participate in a telephone survey about their experience with drug
Important Associations
1.Berkson's bias 2.nonrespondent bias 3.sampling bias
Solutions
1.Random, independent sample
2.weight data |
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Term
•Measurement bias
ex. asking leading questions "You don't like your doctor do you: |
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Definition
◦Information is gathered in a way that distorts the information ◾Hawthorne Effect ◾subjects alter their behavior when they know they are being studied. Ex. select intelligent people who know what your doing.
Important Association
1.Hawthorne effect 2.admission rate bias
Solutions
1.control group/ placebo group |
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Term
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Definition
◦Subjects with the disease are more likely to recall the exposure of interest ◾e.g. parents of children with cancer recall exposure to a chemical
Important Association
1.retrospective studies
Solutions
1.confirm information with other sources
2.confirmation |
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Term
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Definition
◦Patients with severe disease are less likely to be studied, because they die ◾e.g. a group of HIV+ individuals are all asymptomatic
Important Association
1.Early Mortality
Solution
1.Statify by severity |
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Term
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Definition
| ◦Different groups not treated the same |
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Term
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Definition
Early detection looks like increase in survival ◾common with improved screening
Important Association
1.Benefits of screen
Solutions
1.Measure "back-end survival
2.use life-expectancy to assess benefits |
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Term
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Definition
◦Investigator inadvertently conveys his high expectations to subjects, who then produce the expected result
◦A "self-fulfilling prophecy" ◾Golem Effect is the opposite: study subjects decrease their performance to meet low expectations of investigator. |
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Term
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Definition
| ◦The control group is inappropriately non-comparable to the intervention group |
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Term
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Definition
◦Investigator's evaluation is impacted by knowledge of exposure status
Solution
1.blinding study |
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Term
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Definition
•Randomization ◦an intention-to-treat analysis is used in order to preserve randomization
•Use placebo as control
•Blind studies
◦Double blind is best
◦Double blinding means both investigators and subjects are blinded.
•Crossover studies
◦Subject acts as own control
◦Limits confounding |
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Term
| Examples of Effects that are Not Bias |
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Definition
Effect modification
◦Effect modification occurs when a third factor affects the magnitude of the relationship between the exposure and the disease
◾e.g. The increased risk of cancer in smokers is even higher among those who also drink heavily.
◾NOT a type of bias
•Latent period
◦The negative effects of a disease may take years to become clinically apparent
◦NOT a type of bias
•Generalizability
◦the ability to use results from a study to draw conclusiosn about populations different than that used in the study
◦this is most problematic for studies that evaluate only a very specific population |
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Term
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Definition
1° (Primary Prevention)
◦Prevent disease occurrence ◾e.g. Vaccination
•2° (Secondary Prevention)
◦Early detection of disease to either prevent or decrease morbidity from disease before onset of symptoms ◾e.g. Colonoscopy
•3° (Tertiary Prevention) ◦Reduce morbidity from disease after symptom onset ◾e.g. Medication |
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Term
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Definition
Observational (by definition)
•Retrospective (almost always)
•Compares the odds of being exposed between patients with disease and patients without the disease ◦e.g. Patients with cirrhosis are more likely to have been exposed to heavy alcohol use
•Odds Ratio (OR) is measure of disease association ◦OR = (a/b) / (c/d) = ad/bc |
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Term
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Definition
Observational (by definition) ◦Can be either prospective or retrospective
•Compares a group with a given risk factor to a group without the risk factor to see if there is an increased likelihood of developing disease ◦e.g. Patients who drink alcohol are more likely to get cirrhosis
•Relative Risk (RR) is measure of disease association ◦asks, "How much more likely are you to get cirrhosis if you drink alcohol?"
◦RR = [a/(a+b)] / [c/(c+d)] |
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Term
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Definition
Participants alternate receiving intervention and placebo. Type of experimental study design in which subjects are exposed to different treatments or exposed to sub sequentially.
•Participants act as own controls ◦improves power and precision of study |
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Term
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Definition
| •Compares monozygotic and dizygotic twins to measure disease heritability |
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Term
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Definition
| •Compares siblings raised by biologic and adoptive parents to measure influence of environmental vs inherited factors |
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Term
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Definition
Combines data from multiple studies ◦better precision than individual studies
◦improves generalizability of study findings
◦considered to be the highest level of clinical evidence
◦limited by: ◾quality of individual studies
◾bias in study selection |
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Term
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Definition
•Experimental study of medical treatment in humans
• 2 or more treatments (or treatment and placebo) are compared
•Highest quality if ◦Randomized
◦Controlled
◦Double-blinded
•4 phases ◦Phase I ◾Small number of healthy subjects
◾Determines safe dose range and side effects
◦Phase II ◾Small number of diseased patients
◾Refines dosage and safety profile
◦Phase III ◾Large number of diseased patients
◾Confirms effectiveness
◾Compare to standard of care
◦Phase IV ◾Post-marketing surveillance
◾Detects rare or long-term adverse effects |
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Term
| Sensitivity, Specificity, PPV, NPV |
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Definition
These 4 measures describe how well diagnostic tests capture the true presence or absence of disease
•Sensitivity (SN) ◦% with disease who test positive
◦= a/(a+c) = TP/(TP+FN)
•Specificity (SP) ◦% without disease who test negative
◦= d/(b+d) = TN/(FP+TN)
•Positive predictive value (PPV) ◦% positive test results that are true positives (linear to prevelance)
◦= a/(a+b) = TP/(TP+FP)
•Negative predictive value (NPV) ◦% negative test results that are true negatives
◦= d/(c+d) = TN/(FN+TN)
•Cut-off point may be adjusted to optimize sensitivity and specificity, which are inversely related (cut-off point with decreased sensitivity is associated with increased specificity and vice-versa) |
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Term
| Odds Ratio, Relative Risk, Attributable Risk |
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Definition
These measures describe the relationship between a risk factor and a disease
•Odds Ratio (OR) ◦Odds of having disease in expose group / odds of having disease in unexposed group ◾= ad/bc
•Relative Risk (RR) ◦Probablity of getting disease in exposed group / probability of getting disease in unexposed group ◾= [a/(a+b)] / [c/(c+d)]
•Attributable Risk (AR) ◦Risk in exposed group - risk in unexposed group ◾= a/(a+b) - c/(c+d) |
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Term
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Definition
Mean ◦Average of all observation
◦Mean = (sum of all observations)/(sample size)
•Median ◦The middle value of all observations
◦If sample size is odd ◾Median = ((n+1)/2)th largest value
◦If the sample size is even ◾Median = the average of the (n/2)th and ((n/2)+1)th largest value
•Mode ◦The most commonly occurring value
◦If there is more than one most commonly occurring value, there are as many modes as most commonly occurring values |
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Term
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Definition
Normal ◦aka Gaussian, bell-shaped
◦Mean = median = mode
•Bi-modal ◦Distribution has two humps (each being a relative mode)
◦If symmetrical, mean = median
•Skewed ◦Positive Skew ◾Asymmetrical with tail trailing off to right
◾Mean > median > mode
◦Negative Skew ◾Asymmetrical with tail trailing off to left
◾Mean < median < mode
◦Mean very sensitive to skew
◦Median somewhat resistant to skew
◦Mode very resistant to skew |
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Term
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Definition
Null Hypothesis (H0) ◦Hypothesis of no difference ◾i.e. There is no link between disease and risk factor
•Alternative Hypothesis (H1) ◦Hypothesis of difference ◾i.e. There is a link between disease and risk factor |
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Term
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Definition
| http://upload.medbullets.com/topic/1011/images/power%202x2%20table%20color.jpg |
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Term
| Type I error (False positive) |
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Definition
•Stating there is an association when none exits ◦Incorrectly rejecting null hypothesis
•α = probability of type I error
•p = probability that results as or more extreme than those of the study would be observed if the null hypothesis were true ◦General rule of thumb is that statistical significance is reached if p < 0.05 |
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Term
| Type II error (False negative) |
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Definition
•Stating there is no effect when an effect exists ◦Incorrectly accepting null hypothesis
•β = probability of type II error |
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Term
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Definition
•Probability of correctly rejecting null hypothesis ◦Power = 1 - β
•Power depends on ◦Sample size ◾Increasing sample size increases power
◦Size of expected effect ◾Increasing effect size increases power |
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Term
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Definition
| •Probability of correctly accepting null hypothesis |
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Term
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Definition
•Describes the range in which the mean would be expected to fall if the study were performed again and again ◦= range from [mean - Z(SEM)] to [mean + Z(SEM)]
◦95% CI (alpha = 0.05) is standard ◾for 95% CI, Z = 1.96
•Outcomes ◦If 0 falls within the CI when calculating the difference between 2 variables, H0 is not rejected and the result is not significant
◦If 1 falls within the CI when calculating OR or RR, H0 is not rejected and the result is not significant |
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Term
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Definition
Precision ◦Also known as reliability ◾Consistent
◾Reproducible
◾No random variation
•Accuracy ◦Reflects true value
◦No systematic variation |
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Term
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Definition
A method utilized in evidenced based medicine to determine the clinical value of a study
•See details of Clinical Design Trials |
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Term
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Definition
Level 1
1.Randomized Controlled Trial (RCT): ◦A study in which patients are randomly assigned to the treatment or control group and are followed prospectively
Level 2
1.Prospective Cohort Study ◦A study in which patients are assigned to groups in a non-random fashion by exposure (e.g. treatment or risk factor), with the outcome occurring after the initiation of the study
Level 3
1.Retrospective Cohort Study ◦A study in which patients are assigned to groups in a non-random fashion by exposure (e.g. treatment or risk factor), with the outcome occurring before the initiation of the study
2.Case-Control Study ◦A study in which patients are assigned to groups in a non-random fashion by their outcome status (e.g. diseased or not-diseased) and examined for the prior exposure of interest
Level 4
1.Case Series ◦A report of multiple patients with the same disease or treatment, but no control group or comparison group
Level 5
1. Case Report (a report of a single case)
2.Expert Opinion
3.Personal Observation |
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Term
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Definition
◦total cases in population at given time / total population at risk
◦= Incidence * disease duration |
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Term
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Definition
| ◦new cases in population over a given time period / Total population at risk during that time ◾NOTE: people who already have the disease are NOT counted among those at risk when calculating incidence |
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Term
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Definition
•Prevalence > incidence in chronic diseases
•Prevalence = incidence in acute diseases |
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Term
| Leading causes of death in the US |
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Definition
•All Ages ◦Heart disease, cancer, stroke
•<1 year: ◦Congenital anomalies, disorders relating to low birth weight, SIDS
•1-4 years: ◦Injuries, congenital anomalies, cancer
•5-14 years: ◦Injuries, cancer, congenital anomalies
•15-24 years: ◦Injuries, homicide, suicide
•25-44 years: ◦Injuries, cancer, heart disease
•45-64 years: ◦Cancer, heart disease, injuries
•>65 years: ◦Heart disease, cancer, stroke |
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Term
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Definition
•Medicare and Medicaid
•Federal social insurance programs ◦were created as part of the Social Security Act
•Medicare ◦Covers the elderly (65+ years)
◦Also covers ESRD
◦2 main parts
◾Part A pays the hospital
◾Part B pays physicians
•Medicaid
◦For low income people
◦Federal and state components |
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Term
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Definition
•Capitation ◦fixed amount of money per patient per unit of time over which services are rendered
•Fee-for-service ◦physician is paid separately for each service rendered
•Salary ◦fixed amount of money paid physician irrespective of services rendered |
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Term
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Definition
•If the patient cannot make decisions, surrogate decision makers must use the following criteria: ◦subjective standard (advance directive of patient) ◾living will = patient provides specific instructions to withhold or withdraw life-sustaining treatment
◦substituted judgment (what would the patient want) ◾durable power of attorney = patient designates healthcare proxy to make decisions
◾supersedes living will if both exist
◦"best interests" of the patient
◦when no living will or durable power of attorney exists, the clinician is responsible for determining an appropriate surrogate decision maker from available family members ◾the priority of next-of-kin for surrogate decision making is as follows: ◾legal guardian appointed by a court
◾spouse
◾adult children (> 18 yrs)
◾parents
◾adult siblings
◾grandparents/grandchildren
◾friend of the patient
•Euthanasia ◦passively allowing patient to die is acceptable ◾but do everything you can to relieve patient's suffering
◦active killing of the patient is not acceptable
•when treatment should stop ◦physician thinks treatment is futile but family insists on treatment ◾continue treatment
◦after declaraion of brain death but family insists on treatment ◾stop treatment |
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Term
| Capacity, Competence, and Consent |
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Definition
•Capacity vs competence ◦capacity is a medical term
◦competence is a legal term
•Competent patients have the right to refuse medical information and medical treatment(s) ◦a feeding tube is a medical treatment
◦a competent person can refuse lifesaving hydration or nutrition
•Assume that the patient is competent unless ◦history of suicide attempt
◦psychotic
◦patient cannot communicate
•Obtain informed consent ◦patient must understand ◾risks
◾benefits
◾alternatives ◾including no treatment
◦patient must agree with plan of care without coercion
◦exceptions ◾emergencies
◾waiver by patient
◾patient lacks decision-making capacity
◾therapeutic privilege ◾physician deprives an unconscious or confused patient of his autonomy in order to protect the patient's health (paternalism)
◦note that written consent can be revoked orally at any time
◦components of informed consent include: ◾patient makes and communicates a choice
◾patient is informed ◾information has not been withheld from the patient
◾decision remains stable over time
◾decision is consistent with patient's values and goals
◾decision is not result of delusions or hallucinations
◦consent from a patient's spouse is not required treatment of a patient with capacity |
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Term
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Definition
| Type of experimental study design that utilizes >2 interventions and all combinations of these interventions |
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Term
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Definition
| is a form of retrospective observational study in which subsets of controls are matched to cases |
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Term
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Definition
| seeks to determine whether an intervention works in real life conditions. |
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Term
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Definition
| occurs when a study uses a gold stand testing selectively in order to confirm a positive or negative result of preliminary testing. This can result in overestimates or (underestimates) of sensitivity. |
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Term
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Definition
| when the control group unintentionally receives the treatment or the intervention, thereby the difference in the outcome between the control and treatment group. |
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Term
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Definition
| observer selects hospitalized patient as control, group which falsely report due to better monitor and care. |
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Term
| Experiment Expectancy Bias |
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Definition
Researcher's beliefs affect outcome
Important association
1.pygmalion effect
2.interview bias
Solution
Double-blind design |
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