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Absolute Risk Reduction (ARR), Risk Difference (RD), or Attributable Risk (AR)

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The difference in risks of an outcome between 2 experimental groups = EER - CER

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Accuracy

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Truthfulness of results or measurements. requires comparison to known "truth" aka "validity"

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Bias

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Systematic error in study design which may skew the results leading to a deviation from the truth

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Interviewer Bias

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Error introduced by an interviewer's conscious or subconscious gathering of selective data.

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Lead-time bias

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Mistakenly attributing increased survival of patients to a screening intervention when longer survival is only a reflection of earlier detection in the preclinical phase of disease.

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Recall Bias

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Error due to inaccurate recollection of past events or experiences. Particularly relevant to CASE CONTROL STUDIES (CCS).

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Referral bias

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The proportion of more severe or unusual cases tends to be artificially higher at tertiary care centers.

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Selection bias

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An error in patient assignment between groups that permits a confounding variable to arise from the study design rather than by chance alone.

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Spectrum bias

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Occurs because of a difference in the spectrum and severity of disease between the population where the diagnostic test was developed and clinical population that the test is applied to. Diseased subjects in experimental population tend to be the "sickest of the sick" with few FN (Se is over-estimated); eg, Phase I trials Non-diseased subjects in experimental population tend to be the "wellest of the well" with few FP results (Sp is overestimated); eg, Phase II trials

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Verification Bias --- aka, work-up bias, or test-referral

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error that occurs when the decision to conduct the confirmatory or gold (reference) standard test is influenced by the result of the diagnostic test under study this results in an overly optimistic estimate of Se and an underestimate of Sp

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Volunteer Bias --- aka, response bias

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People who choose to enroll in clinical research or participate in a survey may be systematically different (e.g. healthier, or more motivated) than the patients seen clinically

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Blinding or Masking

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purposely denying access to information in order to keep that information from influencing some measurement, observation, or process decreases INFORMATION/MEASUREMENT bias

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Double-blinded

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term that refers to the fact that neither the study subject nor the study staff are aware of which group or intervention the subject has been assigned

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Cochrane Collaboration

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an international group that works to prepare, disseminate, and continuously update systematic reviews of controlled trials for specific patient populations

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Co-intervention

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interventions other than the treatment under study particularly relevant to therapy RCT's, in which case readers should assess whether these ______________ were differentially applied to the treatment and control groups

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Concealment

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associated with randomization randomization schedule of patients hidden from clinicians who entered patients into the trial; therefore the clinician is unaware of which treatment the next patient will receive and therefore cannot consciously or subconsciously distort the balance between groups If this was not performed, you might preferentially enroll those with better prognosis in treatment group. decreases SELECTION bias

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1) blinding/masking : information bias (bl-IN-d : IN-formation) 2) concealment : selection bias ("CEAL-ection" bias)

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1) what kind of bias does blinding/masking reduce? 2) what kind of bias does concealment reduce?

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Confidence Interval (CI)

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a measure of precision surrounding the point estimate

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1) the inherent variability of the characteristic being measured 2) the study sample size: increasing the sample size --> narrowing of C.I.

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what two things affect the width of a confidence interval?

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Confounder or Confounding Variable

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A factor that distorts the true relationship of the study variable of interest by virtue of being related to both the study variable and the outcome of interest. often UN-equally distributed among the groups being compared Randomized studies are less likely to have their results distorted by these factors because randomization should result in the equal balance of these factors at baseline.

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Cost Benefit Analysis (CBA)

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Provides information on both the cost and benefits of intervention, expressed in monetary terms.

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Cost Effectiveness Analysis (CEA)

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Provides information on both cost of an intervention and its effectiveness defined by a metric (NOT by a monetary term) such as cost per life saved or case averted. these types of studies are in principle directly comparable if they use the same metric and same methodologies in calculating costs.

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Cost Only

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Studies documenting costs of road traffic injuries without providing effectiveness or benefit information for actual or potential interventions.

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Cost Utility Analysis (CUA)

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** in EPI 547, this concept is a subset of "CEA"; therefore, sometimes "CEA" is used to refer this more specific concept ** Similar to CEA, but metric in denominator is adjusted for quality of life or utility typically uses Quality Adjusted Life Years (QALYs) or Disability Adjusted Life Years (DALYs) as their metric both QALY and DALY combine information on mortality and morbidity into a single indicator

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Cox Regression Model

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A regression technique for survival analysis that allows adjustment for known differences in baseline characteristics between intervention and control groups when applied to survival data.

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Diagnosis

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The determination of the nature of a disease; a process of more or less accurate guessing

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Differential Diagnosis

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A PROBABILISTIC listing of potential causes of a patients clinical problem which can be ordered in a probabilistic, prognostic, or pragmatic fashion

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Disability Adjusted Life Years (DALYs)

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A negative measure of combined premature mortality and disability - i.e. the health gap between actual and potential health years of life. Death is defined as 1 and perfect health as 0. these measures do not use interaction of types of mortality but rather add up disability weights from different conditions Calculated using population perspective; age weighting places a higher importance on individuals in prime productive age.

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Discount Rate

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All types of economic evaluation of health conditions use some type of discounting to discount future benefits and costs, based on principle that humans value benefits in the present more than they do benefits in the future. In theory, this should be equal to the real interest rate (i.e. actual interest rate minus rate of inflammation) In practice economic evaluation rate is 3%

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Effectiveness (NOT efficacy)

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Measurement of benefit resulting from an intervention for a given health problem under conditions of USUAL practice Considers both efficacy of an intervention and its acceptance by those to whom it is offered Answers the question: "Does the practice do more good than harm to people to whom it is OFFERED?"

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Efficacy (NOT effectiveness)

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A measure of benefit resulting from an intervention for a given health problem under conditions of IDEAL practice. Answers: "Does the practice do more good than harm to people who fully COMPLY with the recommendations?" this is what RCTs are supposed to measure

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Event Rate (Risk or CIR) -- (In an RCT design the terms controlled event rate (CER) and experimental event rate (EER) refer to the risks in the two comparison groups.)

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Calculated as the proportion of a fixed population who develop the event of interest over a period of time.

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Evidence-Based Medicine

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The CONSCIENTIOUS, EXPLICIT, and JUDICIOUS use of current best evidence in making decisions about the care of individual patients. requires integration of individual clinical expertise and patient preferences with the best available external clinical evidence from systematic research

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Generalizability (aka External Validity)

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The extent to which the conclusions derived from a trial (or study) can be used beyond the setting of the trial and the particular people studied in the trial.

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Gold Standard/Reference Standard

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An established method, or a widely accepted method, for determining a diagnosis. It provides a standard to which a new screening or diagnostic test can be compared.

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gold standard/reference standard

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in articles about diagnostic tests, the _________________ must be explicitly acknowledged and applied independently in a blinded fashion.

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Hazard Ratio (HR)

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The relative risk of an outcome (e.g, death) over the entire study period often reported in the context of survival analysis (Cox regression model) has a similar interpretation as the relative risk

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Health

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A state of optimal physical, mental, and social well being; not merely the absence of disease and infirmity (WHO).

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Health Outcome

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All possible changes in health status that may occur in an individual or in a defined population or that may be associated with exposure to an intervention.

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Heterogeneity

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Differences between patients (clinical ________________) or differences in the results of different studies (statistical ________________)

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Human Capital Approach

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Defines costs and benefits in terms of gains or losses in economic productivity. For an individual, injuries or deaths that are costed using this approach include the theoretical future lost wages of the individual who died or was injured.

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Inception Cohort

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A designated group of persons assembled at a common time early in the development of a specific clinical disorder and who are followed thereafter. In assessing articles about prognosis it is critical that this group is well described in order to permit assessment of the homogeneity of the cohort.

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Incidence Rate expressed either as: -- CIR = a percentage or proportion of the number of people at risk ...or... -- IDR = the number of new cases occurring per person time

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Number of new cases of disease occurring during a specified period of time

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Inference

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to arrive at a conclusion the act of taking information from published experience and individualizing to specific patients influenced by the hierarchy and quality of available evidence

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Intention-to-Treat Analysis

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Analyzing patient outcomes based on which group they were randomized into regardless of whether they actually received the planned intervention preserves the power of randomization by maintaining equal distribution of important unknown factors that could influence outcome in each comparison group most conservative and most valid analytics approach for a RCT

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Modified Intention-to-Treat Analysis

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Describes an analysis where the investigators excluded a small number of subjects from the pure ITT population (eg, patients who should not have been enrolled in study or died from unrelated causes shortly after enrollment of unrelated causes)

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Internal Validity

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The degree to which inferences drawn from a specific study are accurate requires a careful assessment of the study's methodology to determine whether the observed findings are accurate Implies that apart from random error the study findings cannot be ascribed to a systematic error or bias; in other words, tells you that the study does NOT suffer from confounding, selection, or information bias to an important degree; thus this term is high in RCT's

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Kappa (K)

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A measure of the RELIABILITY or AGREEMENT between two raters for categorical or qualitative data (eg, two physicians reading x-ray films) adjusts for the agreement that would be expected to occur due to chance alone; therefore aka CHANCE-CORRECTED AGREEMENT Ranges from -1 to +1 > 0.8 = excellent agreement 0.6 - 0.8 = substantial agreement 0.4 - 0.6 = moderate agreement < 0.4 = fair/poor agreement

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Likelihood Ratio (LR)

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A ratio of likelihoods (or probabilities) for a given test result. = (the probability of a given test result occurring in people WITH disease) / (the probability of the very same test result occurring among people WITHOUT disease) Measures the power of a test to change the pre-test into the post-test probability of a disease being present. contrasts the proportions of patients with and without disease who have a given test result

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Matching

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A deliberate process to make the study group and comparison group comparable with respect to factors (or confounders) that are extraneous to the purpose of the investigation but which might interfere with the interpretation of the studies' finding

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Median Survival

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Length of time that one-half of the study population survives.

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Meta-Analysis (MA)

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A systematic review (SR) which uses quantitative tools to summarize the results

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Multivariable Regression Analysis -- multivariable logistic regression: for binary outcomes ("LOG-BIN") -- multivariable linear regression: for continuous outcomes

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A type of regression model that attempts to explain or predict the dependent variable (or outcome variable or target variable) by simultaneously considering 2 or more independent variables (or predictor variables). Used to account for confounding and interaction effects.

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Non-inferiority trials

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Trials undertaken with the specific purpose of proving that one treatment is no worse than another treatment (which is usually the current standard of care). Also includes equivalence trials.

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Number Needed to Harm (NNH) --- for RCT or Cohort use: NNH = 1/ARI --- for Case-Control use when given an OR: NNH = [CER(OR-1)+1] / [CER(OR-1)(1-CER)]

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The number of patients who would need to be treated over a specific period of time before one adverse side-effect of the treatment will occur.

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Number Needed to Treat (NNT) --- for RCT or Cohort use: NNT = 1/ARR --- For CCS use when given an OR: NNT = [1-CER(1-OR)] / [CER(1-CER)(1-OR)]

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The number of patients who need to be treated over a specific period of time to prevent one bad outcome. when discussing this concept, specify the treatment, its duration, and the bad outcome being prevented

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Odds

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A ratio of probability of occurrence to non-occurence of an event = probability / (1-probabilty)

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Odds Ratio

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Used in CASE CONTROL designs to describe the MAGNITUDE or STRENGTH of an ASSOCIATION between an exposure and the outcome of interest used to approximate the RR since the actual underlying disease risks (CIRs) in the exposed and unexposed groups cannot be calculated in a CCS design more closely approximates the RR when the outcome of interest is INFREQUENT or RARE (<10%) = a*d / b*c

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Outcomes

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All possible changes in health status that may occur as a result of following subjects or that may stem from exposure to a causal factor or to a therapeutic intervention.

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P-value

answer

The probability of obtaining the value of the test statistic at least as large as the one observed, under the assumption that the H0 is true; i.e., [ P(data l H0 true) ] The smaller this is, the lower your degree of belief is in the null hypothesis being true used to make a DECISION based on available data, but increasingly used less and less (replaced by confidence intervals)

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Population Attributable Risk (PAR)

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The excess incidence of a given disease in a population that is due to a risk factor = (Attributable Risk or Risk Difference) x (Prevalence of RISK FACTOR in population) = (total incidence of DISEASE) - (incidence of DISEASE in unexposed)

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Population Attributable Risk Fraction (PARF) ---aka "etiologic fraction"

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The fraction of a given disease in a population that is due to a risk factor **Under the assumption that the risk factor is a cause of the disease**, it represents the maximum potential impact on disease incidence if the risk factor was removed = PAR / Total DISEASE Incidence = [ (Prev. of RISK FACTOR) x (RR-1) ] / [ 1+ (Prev. of RISK FACTOR) x (RR-1) ]

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Power

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Ability to detect a difference between two experimental groups if one in fact exists = 1 - Beta

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Precision

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a measure of variability in the point estimate as quantified by the confidence interval influenced by RANDOM error

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Predictive Value Postive (PVP)

answer

proportion of people with a positive test who have the disease.

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Predictive Value Negative (PVN)

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proportion of people with a negative test who are free of the disease

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Prevalence (P, Prev)

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Proportion of persons affected with a particular disease at a specified time can inform clinician's efforts to set anchoring pretest probabilities for their patients; therefore, this term is aka "prior probability" in diagnostic studies

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Prognosis

answer

The possible outcomes of a disease and the frequency with which they can be expected to occur.

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Quality Adjusted Life Years (QALYs)

answer

Combine morbidity and mortality into a positive measure of life lived, with death defined as 0 and perfect health as 1 defined from the individual's perspective, and include interaction of different types of morbidity use discounting of future years, generally at a 3% discount rate

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Randomization

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Allocation of individuals to groups by a formal chance process such that each patient has an independent, equal chance of selection for intervention group.

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Relative Risk (Risk Ratio)

answer

a measure of the EFFICACY or MAGNITUDE of the treatment effect

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Relative Risk Reduction (RRR) = 1 - RR

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the percent reduction in an outcome event in the experimental group as compared to the control group. the proportion of risk that's removed by the intervention Unlike the ARR, this is assumed to be a constant entity - that is, it is assumed not to change from one population (study) to another. It represents a FIXED MEASURE of the EFFICACY of an intervention

question

RELATIVE risk reduction (RRR) is FIXED; it does NOT change from one population to another. [ The ARR, however, is responsive to changes in the baseline event rates. ]

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Which of the following is a FIXED measure of an intervention's efficacy (i.e., which does NOT change from one population to another): --- ARR --- RRR ?

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Relative Risk Increase (RRI) = RR - 1

answer

The percent increase in an outcome in the experimental group as compared to the control group.

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Reliability

answer

Refers to consistency or reproducibility of data (repeatability) Referred to as "agreement" when examining categorical data (see also: "kappa") important to distinguish this from validity

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INTRA-rater reliability

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refers to the consistency/repeatability/reproducibility within the SAME observer or instrument

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INTER-rater reliability

answer

refers to the consistency/repeatability/reproducibility between TWO (or more) observers or instruments

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Receiver Operator Characteristic (ROC) Curves --- "area under the ROC curve" --> "AUROC"

answer

plot test sensitivity (on the y axis) against 1-specificity (on x-axis) for various cut-points of a continuously distributed diagnostic variable the curves describe the tradeoff between Se and Sp as the cut point is changed tests that discriminate well crowd towards the upper north-west corner of the graph used to compare discriminating ability of two or more tests by comparing the area under the curve

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Sensitivity (Se)

answer

The proportion of people WITH disease who have a POSITIVE test or P(T+ l D+)

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SnNout

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When a highly SENSITIVE test is NEGATIVE, it rules OUT the diagnosis of disease

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Sensitivity Analysis

answer

A test of the stability of a study's conclusions by evaluating the outcome over a range of plausible estimates, value judgements, or assumptions.

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Specificity (Sp)

answer

The proportion of people WITHOUT disease who have a NEGATIVE test or P(T- l D-)

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SpPin

answer

When a highly SPECIFIC test is POSITIVE, it rules IN the diagnosis of disease

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Standards

answer

Authoritative statements of *minimal* levels of acceptable performance or results, *excellent* levels of performance or results, or the *range* of acceptable performance or results

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Study Designs

answer

Case Series Case Control Study Crossover Design Cross-Sectional Survey Cohort Study N-of-1 Trial Randomized Control Trial Systematic Review Meta-Analysis

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Case Series

answer

A collection or a report of the series of patients with an outcome of interest No control group is involved

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Case Control Study (CCS)

answer

Identifies patients who have a condition or outcome of interest (cases) and patients who do not have the condition or outcome (controls). The frequency that subjects are exposed to risk factor of interest is then compared between the cases and controls. disease rates CANNOT be directly measured so calculate Odds Ratio

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Case-Control Studies: advantages & disadvantages

answer

Advantages: 1. QUICK & INEXPENSIVE 2. sometimes only feasible method for investigating (a) RARE disorders or (b) when a LONG LAG TIME exists between an exposure of interest and development of the outcome/disease of interest 3. Helpful in OUTBREAK investigations when you need a quick answer followed by a quick response Disadvantages: 1. Recall bias 2. Unknown confounding variables 3. Difficulty selecting appropriate control groups

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Crossover Design

answer

method of comparing 2 or more treatments or interventions in which all subjects are switched to the alternate treatment after completion of the first allocation to first treatment is by random process since subjects serve as their own controls, error variance is reduced

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Cross Sectional Survey

answer

Observation of a defined population at a single point in time or during a specific time interval Exposure and outcome are determined simultaneously. aka PREVALENCE SURVEY b/c prevalence is the only epidemiological frequency measure that can be measured; CANNOT measure incidence rates using this study design

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Cohort Study --- Prospective cohort study: follow-up occurs in a forward direction --- Retrospective cohort study: follow-up is done based on historical information

answer

Involves identification of two groups of patients who are defined according to whether they were exposed to a factor of interest. The groups are then followed over time and incidence rates for the outcome of interest in each group are measured. The ratio of these incidence rates results in the relative risk (RR) which quantifies magnitude of association between factor and outcome (disease)

question

Cohort Studies: advantages and disadvantages

answer

Avantages: 1. Can establish a clear temporal relationship between exposure and disease onset 2. Able to generate incidence rates Disadvantages: 1. Control/unexposed groups may be difficult to identify 2. exposure to a variable may be linked to a hidden confounding variable 3. blinding often not possible 4. no randomization 5. if the disease of interest is rare, a huge sample size and long follow-up is required --> slow & expensive

question

N-of-1-Trial

answer

When an individual patient undergoes pairs of treatment periods organized so that one period involves use of the experimental treatment and the other involves use of a placebo or alternate therapy. Ideally the patient and physician are both blinded, and outcomes are measured. Treatment periods are replicated until patient and clinician are convinced that the treatments are definitely different or definitely not different.

question

Randomized Controlled Trial

answer

A group of patients is randomized into an experimental group and into a controlled group. These groups are then followed up and various outcomes of interest are documented. the ultimate standard by which new therapeutic maneuvers are judged randomization should result in equal distribution of both known and unknown confounding variables into each group (experimental and control) an unbiased study of this type also requires concealment and, where feasible, blinding

question

Randomized Controlled Trial: disadvantages

answer

1. often impractical 2. limited generalizability 3. volunteer bias 4. significant expense 5. sometimes ethically difficult to perform

question

Systematic Review

answer

A formal review of a focused clinical question based on a comprehensive search strategy and structured critical appraisal designed to reduce the likelihood of bias No quantitative summary is generated

question

Meta-Analysis

answer

A systematic review which uses quantitative methods to combine the results of several studies into a pooled summary estimate.

question

Survival Analysis

answer

A statistical procedure used to compare the proportion of patients in each group who experience an outcome or endpoint at various time intervals over the duration of the study (eg, death)

question

Survival Curve --- aka, "Kaplan Meier survival curves"

answer

A curve that starts at 100% of the study population and show the percentage of the population still surviving (or free of disease or some other outcome) at successive times for as long as information is available.

question

Substitute or Surrogate Endpoints

answer

study outcomes that are not immediately significant in clinical patient care examples may include rates of biochemical changes (eg, cholesterol, HbA1C) whereas clinically significant endpoints are more clearly tied to events that patients and their doctors care about most (eg, stroke, renal failure, death).

question

Validity --- aka, "Accuracy"

answer

Truthfulness or believability of study conclusions or the extent to which a test actually measures what it is supposed to measure or accomplishes what it is supposed to accomplish Simply put: "does the data really mean what we think it does?" or "can we believe the results?" implies the presence of a gold standard to which the data can be compared

question

Willingness to Pay (WTP)

answer

a type of cost/benefit analysis measures benefits as the aggregate sum of money that potential beneficiaries of an intervention would be willing to pay for the improvements that they would expect from that intervention provides a methodology to place a financial value on potential gains from an action or intervention

question

PICO P = patients I = intervention C = comparison O = outcomes

answer

you can use this acronym to describe the methods of a study or to formulate a clinical question

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