B8.073 EBM in Practice: Long-Acting Reversible Contraception

Question 1

cross sectional study

Answer 1

“survey”
all data collected at one point in time
defined population; data gathers on exposure and outcome simultaneously

Question 2

strengths of cross sectional studies

Answer 2

relatively quick and inexpensive
can study several exposure and/or diseases simultaneously
can estimate exposure burden and disease burden (prevalence)

Question 3

weaknesses of cross sectional studies

Answer 3

cannot determine exposure-disease temporal relationship
cannot identify incident cases
can miss acute conditions

Question 4

relative rate reduction

Answer 4

change in rate/original rate

Question 5

absolute rate reduction

Answer 5

subtract rates directly

Question 6

mistimed pregnancy

Answer 6

did not want to become pregnant at the time pregnancy occurred, but wanted to become pregnant in the future

Question 7

risk factors for unintended pregnancy

Answer 7

age (younger)
low income
< high school education
co-habitation

Question 8

case-control study temporality

Answer 8

retrospective

pick individuals with conditions and look for exposures

Question 9

temporality of RCT and cohorts

Answer 9

both look forward in time

Question 10

ecologic study

Answer 10

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

Question 11

strengths of cohort studies

Answer 11

establishes temporal relationship between exposure and outcome
good for studying more than one outcome
efficient for rare exposures
can estimate risk

Question 12

weakness of cohort studies

Answer 12

selection bias
if retro:
-information bias
-misclassification bias
if prospective:
-loss to follow up
-resource intensive

Question 13

strengths of ecologic studies

Answer 13

relatively quick and inexpensive
several exposures and/or disease simultaneously
can estimate exposure burden and disease burden
hypothesis generating

Question 14

weaknesses of ecologic studies

Answer 14

ecological fallacy: removes variation from group by treating them as one

Question 15

what is external validity?

Answer 15

how generalizable a study is to the rest of the population

Question 16

what are the US medical eligibility criteria for contraceptive use

Answer 16

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

Question 17

what is alpha?

Answer 17

a representation of confidence level
confidence level = 1- alpha
probability of making type 1 error

Question 18

decreasing alpha

Answer 18

reduces probability of making type 1 error

increases sample size

Question 19

type 1 error

Answer 19

reject the null hypothesis, but your shouldn’t have

-major reason that study results should be replicated in other studies

Question 20

what is beta?

Answer 20

a representation of study power
power = 1-beta
probability of making a type 2 error

Question 21

decreasing beta

Answer 21

reduces probability of making type 2 error

increases sample size

Question 22

type 2 error

Answer 22

when you don’t reject the null hypothesis, but you should have
-often occurs due to inadequate study power

Question 23

how to power a study to detect a large difference

Answer 23

decrease sample size

Question 24

how to power a study to detect a small different

Answer 24

increase sample size

Question 25

hawthorne effect

Answer 25

subject alters behavior when they know they are being studied

Question 26

observer bias

Answer 26

investigator’s evaluation is impacted by knowledge of exposure status

Question 27

procedure bias

Answer 27

exposure and control group not treated equally

Question 28

recall bias

Answer 28

subjects provide inaccurate data (information bias)

Question 29

selection bias

Answer 29

study population not representative of intended source population

Question 30

strengths of RCTs

Answer 30

minimizes impact of bias

• controlled assignment of exposure
• uniform application of exposure and observation
• establishes temporal relationship between exposure and outcome
• prospective observation

Question 31

weaknesses of RCTs

Answer 31

not always feasible
resource intensive
loss to follow up