# Biostats & Epi for PM Flashcards

Fetal Death Rate Equation

total number of fetal deaths in a given time period/total number of live births during the same period of time x 1000

Infant Mortality Rate Equation

total number of deaths of infants (<1 y/o) in a time period/total number of live births during the same period x 1000

Maternal Mortality Rate Equation

deaths due to pregnancy related illness in a given time period/total number of live births during the same period of time x 100,000

Neonatal Mortality Rate Equation

total number of deaths of neonates (<28 days old) in a given time period/total number of live births during the same period of time x 1000

Perinatal Mortality Rate Equation

neonatal deaths + fetal deaths in a given time period/total number live births and fetal deaths during the same time period x 1000

ecological fallacy definition

an association at the population level is not necessarily true at the individual level

studies with ecological fallacy

cross-sectional studies

vital statistics recorded (4)

birth, death, marriage, divorce

length bias definition

when a less aggressive disease appears to have a higher incidence because slower-moving diseases are more likely to be detected

non differential bias is the same as

random error

lead time bias definition

appearance that early diagnosis of a disease prolongs survival

Hawthorne effect definition

individual behavior changes when a person knows they are being observed

regression to the mean definition

the further a value is from the mean, the more likely future recordings are closer to the mean

Neyman bias definition

selective survival bias

cases in a study have different exposures than the ones that die

When does stratification reduce confounding?

analysis stage

3 ways to reduce confounding during the design stage

randomization

restriction

matching

3 ways to reduce confounding during the analysis stage

standardization

stratification

statistical modeling

Bayes theorem equation

(prevalence)(sensitivity)/(prevalence)(sensitivity) + [(1-prev)(1-specificity)]

incidence density definition

number of new cases of a disease per summation of time that each person is at risk of a disease in a specified time and place

incidence density equation

new cases/sum of person-time

central limit theorem definition

when there are a large amount of mutually independent random variables, the mean population will approach normal distribution (n >30)

IQ mean and SD

100 +/- 15

z-score definiton

how many standard deviations are between an observed value and the mean

z-score equation

observed value - mean / standard deviation

rule of addition equation

event 1 + event 2 - (event 1 and event 2 overlap) = probability

used for non-mutually exclusive events

standard mortality ratio equation

observed # of deaths/expected # of deaths x 100

direct adjustment

when you use a second population to extrapolate estimates

null hypothesis definition

there is no difference between the variables being tested

type 1 error definition

when a null hypothesis is rejected when it is actually true (ex. false-positives)

type 2 error definition

when a false null hypothesis is not rejected (ex. false negatives)

confidence interval equation

mean +/- 1.96(std dev/sq root N)

as prevalence increases, PPV _____ and NPV ____

increases, decreases

power equation

1 - beta = 1- the probability of rejecting the null when the null is true

3 ways to increase power

increase sample size

decrease beta

increase threshold of Ho

NNT equation

1/ARR = 1/risk exposed - risk unexposed

NNH Equation

1/absolute risk increase

9 components to determine causality

- consistency of association
- strength of association
- specificity
- temporal factors
- coherence of explanation
- biological plausibility
- experimental evidence from a controlled trial
- dose-response relationship
- analogy

Standard error equation

std dev/sq root n

internal validity definition

how well a study represents the true association within a study

external validity definition

how well the results of a study are generalizable to a different population

degrees of freedom equation

(rows-1)(columns-1)

chi squared equation

sum of (observed data-expected data)sq/expected data

expected= (rows)(columns)/total

Kappa equation

observed agreement/chance agreement/total number-chance agreement

observed: agreed true + agreed false

cell agreement due to chance = (row total)(column total)/(total number)

chance agreement = TT chance + FF chance

F test

part of ANOVA

confounder definition

3rd variable associated with the exposure and the outcome

obscured the relationship between the exposure and outcome

effect modifier definition

changes the relationship between exposures and outcomes

intervening variable defintion

a mechanism by which a causal variable leads to an outcome

necessary cause definition

required for disease to occur but may not invariable lead to disease

sufficient cause definition

invariably leads to a disease

coefficient of determination definition

the proportion of variation of a dependent variable that can be explained by an independent variable

3 examples of time-series analysis

cohort studies

epidemic studies

longitudinal data

McNemar’s Test definition

chi-sq test for non-independent variables, allows you to analyze matched pairs or calculate before and after in the same variable

Mann-Whitney U test definition

tests the median between two groups, the nonparametric version fo the t-test

attributable risk equation

a/a+b - c/c+d

relative risk equation

(a/a+b)/(c/c+d)