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108 Cards in this Set
 Front
 Back
Definition: Range

(Largest variable)  (Smallest variable)


Definition: Variance

The spread of the variables in the distribution


Definition: Standard Deviation

The square root of the variance.


Normal distribution: % of variables in the distribution one standard deviation above and below the mean.

68%


Normal distribution: % of variables in the distribution two standard deviations above and below the mean.

95%


Normal distribution: % of variables in the distribution three standard deviations above and below the mean.

99%


Definition: Zscore

The number of standard deviations above a mean where a variable lies.


Definition: Percentile

# of variables at or below that level.


Definition: Interquartile range

The range of values between the 25th and 75th percentile.


Definition: Left skewed distribution

Tail on left. Mode on right.


Defintion: Right skewed distribution

Tail on right. Mode on left.


Definition: Tdistribution

Different distribution for each sample size


Central limit theorem

Given a sufficiently large sample size, a sample drawn from the population will be normally distributed regardless of the shape of the original population distribution.


Definitions: Standard Error of the Mean (descriptive and mathematical definitions)

Descriptive: Variability in a distribution of sample means


Which is larger: standard error the mean OR standard deviation

standard deviation


Definition: 95% confidence interval

the interval such that the true value has a 95% probability of lying within


Definition: Pvalue

Given the null hypothesis is true, the probability off getting a result as extreme or more extreme than the observed outcome by chance alone.


Definition: Alpha value

The value used to compare the pvalue to to determine if it is significant.


Pvalue > Alpha value: Conclusion?

Results are likely due to chance alone and are not statistically significant.


Pvalue <= Alpha value

Results are unlikely due to chance alone and are statistically significant.


Definition: Null hypothesis

There is no difference between the groups being assessed.


Definition: Alternative hypothesis

There is a difference bbetween the two groups being assessed.


Definition: Twotailed alternative hypothesis

The two groups' values are not equal. (no more specific than that)


Definition: Onetailed alternative hypothesis

One groups' values is less than those of the other group


Definition: Type 1 (Alpha) Error

Incorrectly rejecting the null hypothesis ( a false positive conclusion)


Definition: Type 2 (Beta) Error

Failure to reject the null hypothesis when the alternative hypothesis is correct (a false negative conclusion)


Definition: Power

The probability of finding a specified difference, or larger, when a true difference exists


The difference between statistical significance and clinical significance

Statistical significance only comments on chance, not benefit to patient.


Generally, minimum power for a clinically relevant difference

80% or more


Problem with performing multiple tests without adjusting error

Increases probability of a Type 1 error.


Bonferroni correction

Divide alpha by number of statistical tests to perform to yield a new alpha.


The name for the type of correction where alpha is divided by the number of statistical tests to perform.

Bonferroni Correction


Difference between parametric and nonparametric tests

Parametric: performed on data that are normally distributed


Chisquare test

Performed on discrete data


Fisher's exact test

Performed on discrete data


The other name for the Student ttest

two sample ttest


The other name for the two sample ttest

Student ttest


Student ttest/Two sample ttest

Performed on normally distributed data


One sample ttest

Performed on normally distributed data


What does ANOVA stand for?

ANalysis


ANOVA

Performed on normally distributed data


Paired ttest

Performed on normally distributed data


Correlation

Performed on normally distributed data


Pearson's Correlation coefficient

aka rho


Rho

aka Pearson's Correlation coefficient


Spearman Rank Correlation

Performed on nonnormally distributed data


Rsquared

aka Coefficient of determination


Coefficient of Determination

aka Rsquared


Multiple regression analysis

Has two or more independent variables


Logistic regression analysis

Performed when the dependant variable is binary


Primary screening

Peformed to prevent a disease


Secondary screening

Peformed to reduce the impact of a disease


Sensitivity

Given disease is present, the probability of testing positive


Specificity

Given disease is absent, the probability of testing negative


Predictive value positive

Given the test is positive, the probability that the disease is present


Predictive value negative

Given the test is negative, the probability disease is absent


Types of descriptive studies

Case Report


Difference between a case report and a case series

One versus multiple interesting observations


Correlation study

Descriptive study done on large populations (the per capita meat consumption of a town and the prevalance of CAD there)


Prevalance study

aka CrossSectional study


Stratified Random Sample

Sample is first stratified into groups, and then subjects are tne randomly drawn from each group.


Types of analytic studies and how their subjects are selected

Case Control (Outcome, then exposure is assessed)


Randomized Controlled Trial: Pros

goldstandard


Randomized Controlled Trial: Cons

May take time = $ and losstofollowup of subjects


Prospective Cohort Study: Pros

generates incidence data


Prospective Cohort Study: Cons

bad for rare outcomes


Retrospective Cohort Study: Pros

easy to do, so less $


Retrospective Cohort Study: Cons

bad for rare outcomes


Case Control: Pros

good for rare disease


Case Control: Cons

subject to several biases as recall bias, interview bias, selection bias


Metaanalysis: Pros

increases power by combining study results


Metaanalysis: Cons

Studies not done exactly the same way


Difference between intentiontotreat analysis and efficacy analysis, and which is prefered by the FDA

Intention to treat: All subjects analyzed by study arm, regardless of compliance


Phase One Study

Safety


Phase Two Study

Efficacy


Phase Three Study

Compares new treatment to standard therapy


Prevalance

The proportion of subjects in a group with a certain disease, includes new and old cases (a snapshot in time)


Incidence

New cases occurring over a defined period of time


Cumulative Incidence

aka Attack Rate


Attack Rate

aka Cumulative Incidence


Incidence Rate

aka Density


Density

aka Incidence Rate


Relationship of Prevalence to Incidence Rate

Prevalence = (Incidence Rate)(Average Duration of Disease)


Absolute Risk

The probability of going from a healthy state to an ill state (eg the probability that person x will develop condition y over the next z years when they don't have it already)


Relative Risk

The strength of association between an exposure and outcome.


(xy): x: exposure, y: disease

0=negative, 1=positive


Relative Risk (calculated from prevalances)

Relative Risk = Prevalence of disease in population A divided by Prevalence of disease in population B


Odds Ratio

An approximation of relative risk used in case control studies.


(xy): x: exposure, y: disease

0=negative, 1=positive


Attributable Risk

Excess disease in the exposed population that can be attributed to the exposure


(xy): x: exposure, y: disease

0=negative, 1=positive


Confounding

An erroneous study conclusion when a factor is associated with an exposure and is itself an independent risk factor for the outcome


Ways to control for confounding

Restriction (subjects with known risk factors are excluded)


Effect Modification

aka Interaction


Surveillance Bias

One cohort is followed more closely than another and is thus more likely to be diagnosed with the disease, leading to a difference in risk estimation between the two cohorts


Interaction

aka Effect Modification


Herd immunity

Disease protection of an unimmunized individual because the population is immunized


Epidemic curve

Plots an epidemic by:


Kaplan Meier survival cuves

Shows survival of different groups over time.


Bias

A systematic error with a study leading to an erroneous estimation of the association between the exposure and the outcome


4 major types of bias

Recall bias (differential recall of exposure status by individuals based on their health status)


Criteria for causeeffect relationships

Strength of association (how large or small is the relative risk/odds ratio


Definition: Epidemic

Greater than expected disease frequency in a defined population


Definition: Pandemic

Greater than expected disease frequency in a large defined area


Definition: Endemic

Constant presence of a disease in a defined population


Case Fatality Rate

Proportion of patients with a disease who die of that disease


Mortality Rate

Proportion of patients who die of a disease in a defined population


Key difference between Case Fatality rate and Mortality Rate

The denominator:
