B8.073 EBM in Practice: Long-Acting Reversible Contraception Flashcards
cross sectional study
“survey”
all data collected at one point in time
defined population; data gathers on exposure and outcome simultaneously
strengths of cross sectional studies
relatively quick and inexpensive
can study several exposure and/or diseases simultaneously
can estimate exposure burden and disease burden (prevalence)
weaknesses of cross sectional studies
cannot determine exposure-disease temporal relationship
cannot identify incident cases
can miss acute conditions
relative rate reduction
change in rate/original rate
absolute rate reduction
subtract rates directly
mistimed pregnancy
did not want to become pregnant at the time pregnancy occurred, but wanted to become pregnant in the future
risk factors for unintended pregnancy
age (younger)
low income
< high school education
co-habitation
case-control study temporality
retrospective
pick individuals with conditions and look for exposures
temporality of RCT and cohorts
both look forward in time
ecologic study
groups rather than individuals
exposures and outcomes from existing data sets are averaged for the groups aggregate data
examines associations between average exposure levels and overall outcome rates at the group level
strengths of cohort studies
establishes temporal relationship between exposure and outcome
good for studying more than one outcome
efficient for rare exposures
can estimate risk
weakness of cohort studies
selection bias if retro: -information bias -misclassification bias if prospective: -loss to follow up -resource intensive
strengths of ecologic studies
relatively quick and inexpensive
several exposures and/or disease simultaneously
can estimate exposure burden and disease burden
hypothesis generating
weaknesses of ecologic studies
ecological fallacy: removes variation from group by treating them as one
what is external validity?
how generalizable a study is to the rest of the population
what are the US medical eligibility criteria for contraceptive use
outline safe use of contraceptive methods by women and men
target health care providers
purpose:
-assist health care providers when counseling patients about contraceptive use
-serve as clinical guidelines
what is alpha?
a representation of confidence level
confidence level = 1- alpha
probability of making type 1 error
decreasing alpha
reduces probability of making type 1 error
increases sample size
type 1 error
reject the null hypothesis, but your shouldn’t have
-major reason that study results should be replicated in other studies
what is beta?
a representation of study power
power = 1-beta
probability of making a type 2 error
decreasing beta
reduces probability of making type 2 error
increases sample size
type 2 error
when you don’t reject the null hypothesis, but you should have
-often occurs due to inadequate study power
how to power a study to detect a large difference
decrease sample size
how to power a study to detect a small different
increase sample size
hawthorne effect
subject alters behavior when they know they are being studied
observer bias
investigator’s evaluation is impacted by knowledge of exposure status
procedure bias
exposure and control group not treated equally
recall bias
subjects provide inaccurate data (information bias)
selection bias
study population not representative of intended source population
strengths of RCTs
minimizes impact of bias
- controlled assignment of exposure
- uniform application of exposure and observation
- establishes temporal relationship between exposure and outcome
- prospective observation
weaknesses of RCTs
not always feasible
resource intensive
loss to follow up
