Biostatistics Flashcards by Silver Gold

RRR

Relative Risk Reduction

1-RR

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Relative Risk

Risk of Tx/Risk of Control

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A coffee creamer company recently learned that several lots ofproductwere contaminated with a human carcinogen. It is unknown what effect consuming this carcinogen in small quantities may have on humans. An immediate recall is announced. A massive media campaign is underway to identify people who used the lots of coffee creamer so they can receive medical attention immediately. The company plans to conduct a study to determine the effects of this exposure. They willfollowpeoplewho used the contaminated creamer over time and compare the rates of cancertopeople who used their coffee creamer, but who were not exposed to the contaminated lot. What study design does this trial represent?

A. Cross-sectional study

B. Case series

C. Case-control study

D. Cohort study

E. Case report

Cohort study

This is a prospective cohort study design.

Cohort studies start with an exposure/intervention and look for an outcome of interest (disease).

In this case the study starts with the exposure (contaminated coffee creamer) and patients will be followed prospectively to look for an outcome (disease such as cancer).

This design is useful when randomization to the exposure would be unethical.

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Case-Control Study

Compares pts w/ a disease (cases) to those w/out the disease (control)

Retrospective

Start w/ disease looks for exposure

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Cohort Study

Compares outcomes of a group of pts exposed & not exposed to a Tx

Prospective

Retrospective - less common

Start w/ exposure looks for disease

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Cross-sectional Survey

Estimates the relationship between variables & outcomes (prevalence) at one particular time (cross-section) in a defined population

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Case Report & Case Series

Describes an adverse rxn or a unique condition that appears in a single pt (case report) or a few pts (case series)

Outcome of the case is known

Case series is more reliable than a case report

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Randomized Controlled Trial (RCT)

Compares experimental Tx to a control (placebo or existing Tx)

Pts are randomized (have equal chance of being assigned to the Tx or control)

Sometimes blinded (unaware if they are receiving Tx or control)

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Randomized Controlled Trial (RCT)

Double-blind

Pt & investigator are unaware

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Randomized Controlled Trial (RCT)

Single-blind

Pt is unaware

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Randomized Controlled Trial (RCT)

Open label

or Unblinded

All parties know which Tx is being given to the pt

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Randomized Controlled Trial (RCT)

Parallel

Subjects are randomized to the Tx or control arm for the entire study

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Randomized Controlled Trial (RCT)

Crossover

Pts are randomized to 1 of 2 sequential Txs:
Group 1 - receive Tx A 1st, then crossover (change) to Tx B
Group 2 - receive Tx B 1st, then crossover (change) to Tx A

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Factorial Design

Randomizes to more than the usual 2 groups to test a number of experimental conditions

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Meta-analysis

Combines results from multiple studies in order to develop a conclusion that has greater statistical power than is possible from the individual smaller studies

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Systematic Review Article

Summary of the clinical literature that focuses on a specific topic or questions

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Types of Medical Studies

Least to Most Reliable

Expert Opinion

Case series & Case Report

Cast-Controlled Studies

Cohort Studies

Randomized Controlled Trials

Systematic Reviews & Meta-Analyses

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OR Formula

AD/BC

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Odds/Hazard Ratio

> 1

↑ in the likelihood

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Odds/Hazard Ratio

< 1

↓ in the likelihood

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Odds/Hazard Ratio

= 1

no correlation

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Odds Ratio

How to express OR > 1 in %?

OR x 100 - 100

A pharmacist is considering which beta-blocker should be the preferred formulary agent at his institution. He has narrowed hisselection down to two agents. Each drug provides similar health benefits, has similar tolerability and is dosed once daily. The pharmacist will base his decision on the drug that can be purchased at the lower cost. This type of evaluation can be described as:

A. A cost-minimization analysis

B. A cost-effectiveness analysis

C. A cost-control analysis

D. A cost-benefit analysis

E. A cost-utility analysis

A cost-minimization analysis

If the benefit of two drugs or interventions is considered equivalent (e.g., there is no clinical benefit or harm of one compared to the other), a cost-minimization analysis can be used to determine which treatment is less expensive.

The rate of the primary outcome was 1.28% per year in the apixaban groupand 1.60% per year in the warfarin group (95% CI, 0.66 to 0.95; p < 0.001 for noninferiority; p = 0.01 for superiority).

In this trial, the primary outcome is reported as a hazard rate (rate per year). Calculate the hazard ratio of the primary outcome in patients receiving apixaban compared to warfarin.(Express the answer as a decimal; no units or commas; round the final answer to the nearest TENTH.)

0.8

Hazard ratio (HR) = 1.28%/1.6% = 0.8. It is calculated in a similar way as risk ratio.

When HR < 1, this is favorable for the study drug as it means there were fewerunfavorable events in the treatment group.

HR formula

Hazard rate Tx/Hazard rate Control

Continuous Data

Data is provided by some type of measurement Ratio & Interval

Ratio Data

0 = None

Interval Data

0 does not equal none

Discrete Data

Categorical Nominal & Ordinal

Nominal Data

arbitrary order

Ordinal Data

ranked in a logical order

Student's T-test

Continuous Data 2 independent groups

Paired T-test

Continuous Data 2 paired groups

ANOVA

Continuous Data ≥ 3 independent/paired groups

Chi-Square

Nominal Data ≥ 2 independent groups

McNemar

Nominal Data 2 paired groups

Cochran's Q

Nominal Data ≥ 3 paired groups

Wilcoxon Rank Sum

Ordinal Data 2 independent groups

Wilcoxon Signed Rank

Ordinal Data 2 paired groups

Kruskal-Wallis

Ordinal Data ≥ 3 independent groups

Friedman

Ordinal Data ≥ 3 paired groups

Incremental Cost Rations Formula

(C2 - C1)/(E2 - E1)

Cost-Minimization Analysis (CMA)

Compares cost of interventions w/ demonstrated equivalence

Cost-Benefit Analysis (CBA)

Compares benefits & costs in monetary units

Cost-Effectiveness Analysis (CEA)

Most common Costs are monetary but outcomes are in clinical units (easty to quantify)

Cost-Utility Analysis (CUA)

Outcomes based on quality-of-life assessments

Intent to Treat

Data from ALL pts even the ones who did not complete the study

Per Protocol

Data from ONLY the pts who completed the study

The definition of sensitivity is best represented as: A. The percentage of patients without a disease who have a negative test result. B. The probability that an event will or will not occur. C. The effect of an independent variable on a dependent variable. D. The percentage of patients with a disease who have a positive test result. E. The percentage of patients that will benefit from an intervention when a test result is positive.

The percentage of patients with a disease who have a positive test result. ## Footnote Sensitivity is the percentage of "true-positive" results (a test is positive and the patient has the disease).

Sensitivity

"True Positive" Test is positive in patients w/ the condition

Specificity

"True Negative" Test is negative in patients w/out the condition

A clinical trial is conducted on a new drug, LoSod. LoSod is found to reduce mean serum sodium to 131 mEq/L (95% confidence interval: 128.7 mEq/L - 133.3 mEq/L). What is the correct interpretation of this study result? A. There is a 95% chance that the confidence interval range contains the true population value for reduction in serum sodium with LoSod. B. When using this drug in a larger population, 95% of patients will have a serum sodium between 128.7 and 133.3 mEq/L. C. When using this drug in a larger population, there is 95% confidence that the serum sodium will be reduced to 131 mEq/L. D. There is a 5% chance that the true population mean is within the stated range. E. There is more than a 5% chance that the results of the study are rejected in error.

There is a 95% chance that the confidence interval range contains the true population value for reduction in serum sodium with LoSod. ## Footnote A confidence interval is a range of values which is likely to include the "true" population value. It is more helpful than the p-value in estimating the effect of the outcome on the general population.

A small, randomized, double-blind trial was conducted to evaluate a new treatment in patients with acute myocardial infarction. The primary endpoint, reduction in all-cause mortality, was not statistically significant. Which of the following is an accurate conclusion? A. The inclusion and exclusion criteria were not defined appropriately to reach statistical significance. B. Further studies of the treatment should be discontinued immediately. C. If there was any reduction in mortality, the treatment should be recommended for use. D. A type I error may have occurred, preventing the ability to detect statistical significance. E. The clinical trial may not have adequate statistical power.

The clinical trial may not have adequate statistical power. ## Footnote Performing a larger trial will increase statistical power, which increases the probability that a type II error (not finding a difference when there is a difference) will be avoided.