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70 Cards in this Set
- Front
- Back
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Validity
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does it measure what we think it does
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Reliability
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repeatability, will it give same result over and over (at different times and with different examiners?
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What is the best test for reliability?
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Kappa
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What does a high kappa show?
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Better reliability, don’t use a test with kappa less than .60
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How do you evaluated diagnostic procedures?
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Validity and reliability
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How do you assess validity of a diagnostic?
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Blind comparison with a gold standard
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How do you do a blind comparison with a gold standard?
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ID groups of sick and healthy, administer a new test in a blinded manner, calculate percent of correctly identified subjects with regard to gold standard
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Sensitivity
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the probability of a positive test result when the disease is present
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Specificity
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probability of a negative test result when the disease is absent
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PPV
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probability that the patient has the disease when the test is positive
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NPV
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probability that the patient does not have the disease when the test is negative
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Effect of disease prevalence
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as the prevalence of a disease decreases the PPV of the diagnostic test gets worse (an increase in false positives)
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Criteria for acceptance of a new diagnostic
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has safety, validity, and reliability been shown? Does it add anything to the diagnostic test which precedes it? Advantages in cost/speed/comfort? Will it cause you to change your treatment plan?
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Prospective research study
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designed to answer specific questions about biomedical or behavioral interventions (drugs, treatments, devices, or new ways of using known drugs, treatments, or devices
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Clinical trials
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used to determine whether new biomedical behavioral interventions are safe, efficacious, and effective
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Efficacy
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does the treatment work under ideal conditions?
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What is the focus on for efficacy?
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Internal validity
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Internal validity
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the integrity of the experiment itself, ability to draw a causal link between your treatment and the dependent variable of interest
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Effectiveness
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does the tx work under real-life conditions? |
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What is the focus on for effectiveness?
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External validity
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External validity
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ability to generate your study findings to the population at large
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Things bias can affect
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trend of results, internal and external validity
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Confounding variables
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some aspect of a subject that is associated with both the outcome of interest and with the intervention of interest
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What do confounding variables produce?
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Alternative, competing explanations for an effect
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what can you do to reduce confounding variables?
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Measure baseline characteristics of subjects at initial recruitment (prognostic factors—smoking, medications, hx of periodontal disease)
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examples of confounds
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noncompliance, tx received outside the study, pt on placebo receives active tx, incorrect timing of follow up, incorrect dx, biased assessment of endpoint, biased admin of care
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how can you control confounders?
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Holding confounding variable constant, rely on randomization, matching (similar intervention groups w respect to important prognostic factors), stratification (division of participants into subgroups to categorical prognostic factors), post-study subgroup analysis (no fishing), statistical control (analysis of covariance)
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what is the gold standard of study designs?
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RCT
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how are RCTs designed?
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To minimize bias through randomization and blinding—internal validity |
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what can RCTs provide?
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Sound evidence of causation
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how does crossover design work?
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Each patient is his or her own control, receive tx, washout, next tx
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how does split mouth work?
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Each pt own control, diff tx on each side of mouth or quad
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random sampling
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every member of the population has an equal and independent chance of being selected
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convenience sampling
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take every patient from the accessible population who meets the selection criteria over the specified time period
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stratified sampling
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if the outcome being measured is rare in populations as a whole, recruit at random or consecutively from populations at high risk of the condition in question
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power of a statistical test
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probability that the study sample will yield statistically significant results when there truly is a treatment effect (aka clinically important difference) in the target population
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statistical significance
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the observed difference is greater than zero and unlikely to have occurred by chance alone
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clinical significance
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the smallest difference that would make a meaningful difference in patients lives or clinicians practice
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alpha level
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significance level, or probability of rejecting the null hypothesis when the null hypothesis is true
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simple randomization
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all subjects have an equal and independent chance of being allocated (must truly be a chance process)
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what do control groups allow for?
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Isolation of patient outcomes caused by the test treatment from outcomes caused by other factors
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analysis by intention to treat
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all subjects are analyzed in the groups to which they were assigned, regardless of what happened in the study, tests the effects of assigning patients to treatments (external validity)
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analysis by treatment received
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tests the effects of administering treatments
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registration of RCT
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establishes baseline for judging quality of trial, must be registered prior to consideration for publication, register before you recruit
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CONSORT
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consolidation standards of reporting trials
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Phase 0
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pharmacodynamics/kinetics, first human trials 10-15 subjects
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Phase 1
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20-80 subjects, determine tolerance, metabolism ,kinetics,bioavailability, toxicity and major SEs, establish a safe dose range, relatively high risk
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Phase 2
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establish the testing protocol, 100-300 subjects, gather info on effectiveness on actual clinical endpoints in the targeted indication, ID MC sort term SEs and risks, determine dose ranges for phase 3
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Phase 3
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1000-3000 subjects, adequate well controlled study (RCT), demonstrate efficacy and safety, overall risk/benefit, provide info for labeling
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Phase 4
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post marketing surveillance, ID less common and long term SEs, compare to other marketed products, study new patient populations or new indications
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Power analysis
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preferred method to determine number of subjects in your study
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Type of study with the poorest internal validity
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case study
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Type of study with the best external validity
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meta analysis
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Narrative review
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broad topic, few inclusion criteria, susceptible to bias, non-reproducible
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Systematic review
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narrow topic, exhaustive lit search, strict inclusion/exclusion
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Dimensions of quality in an SR
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clearly stated question, search strategy, things in duplicate, inc.excl, quality of included studies, results
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Why perform a meta analysis?
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Increases statistical power, improve precision, settle controversies from conflicting studies or generate new hypotheses
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What do M-A’s do?
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Derive meaningful conclusions from data and help prevent errors in interpretation
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Heterogeneity
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any kind of variability among studies (clinical—participants, interventions; methodologic—trial design, quality; statistical)
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Measurements of heterogeneity
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Q test (chi squared) or I^2 (for quantifying inconsistency across included studies—0-40% might not be impt, 30-60 moderate, 50-90 substantial, 75-100 considerable)
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Standardized mean difference
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used when trials assess the same outcome but measure in a variety of ways, including different scales
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Risk ratio
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risk/prob/chance of the occurrence of an event in tx relative to control
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Odds ratio
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odds of an even occurring to it not occurring for tx relative to control
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interpretation of a chi square test |
a large chi squared statistic relative to its degrees of freedom provides evidence of heterogeneity |
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what is an I^2 used for |
quantifying inconsistency among included studies |
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NNT |
number of pts needed to treat to prevent one bad outcome |
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how does CI relate to sample size |
inverse sqrt ratio, therefore smaller samples generate wider intervals, if you want to cut margin of error in half then quadruple the SS |
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internal validity associated with effectiveness or efficacy |
efficacy |
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internal validity related to the experimental conclusions |
the ability to draw a causal link between your treatment and the dependent variable of interest |
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clinical trials are used to... |
determine whether new biomedical or behavioral interventions are safe, efficacious, and effective |
