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)