Test 10/24 Flashcards
Dependent variable
what you think the effect of the independent variables will be seen in
Independent variable
YOU vary this in the experiment…. want to see effect on dependent variable
Null hypothesis
states there is NO relationship between the proposed independent and dependent variables
STUDY NEEDS TO PROVE THIS IS NOT TRUE and reject the null hypothesis
Ecologic study
Looks at POPULATIONS only
understand relationship between outcome and exposure at the population level
…. analyses in which the presence of a suspected risk factor is measured in different populations and compared with the frequency of disease onset
Ecologic fallacy
when incorrect conclusions are drawn from ecologic data due to an association at the group level that does NOT persist to the individual level
Association is NOT
causation
Normal distribution– relationship of mean, median, mode
they are all equal
standard deviation
measure of how tightly different data points gather around the mean
The number of standard deviations away from the mean a value lies in a normal distribution tells you…..
how likely that value is to occur
Standard deviation deals with
members of a population
standard error
standard deviation/ square root of the number of all possible samples
expected variability in measurement of a population mean seen in multiple trials
standard error deals with
samples (groups of individuals, aka sample means)
If you have a bigger sample size, the standard error is
LESS and the estimate of the population mean is MORE precise
narrower curve
if you have a smaller sample size, the standard error is
MORE and the estimate of the population mean is LESS precise
wider curve
Prevalance
the number of EXISTING cases of a condition in a population at a MOMENT of time
expressed as a percent
Incidence
the number of NEW cases of a disease that develop in a population over a specified period of time
Incidence requires what 3 things
1) new events
2) population at risk
3) passage of time
What are the two ways to calculate incidence?
Cumulative incidence (risk)
incidence rate
Cumulative incidence (RISK)
= new cases of disease/ total population at risk
Biggest flaw of cumulative incidence
best for fixed populations… does not account for people moving away/ dying etc
Incidence rate
= new cases of disease / total person-time at risk
expressed as a round number…. ie. 1.6 cases per 1000 person-years (usually, multiple number to get in terms of 1000 person-years)
Prevalance of disease (entrance and exits)
incidence ENTERS
cure, death, moving away EXITS
What are three ways to compare the risk in the expose and unexposed groups?
relative risk
absolute risk difference
number needed to treat
Relative risk
risk exposed/ risk unexposed
the probability an event will happen in an exposed group vs. probability an event will happen in a non-exposed group