Faepidemiology: First Aid For Step 2 Ck

Front 1

How to measure incidence.

Back 1

Cohort

Front 2

define prevalence

Back 2

number/proportion of cases in the population at a specific moment in time

Front 3

define incidence

Back 3

number of new cases that arise in the disease free population over a period of time

Front 4

if mortality of a disease decreases, what happens to prevalence?

Back 4

increased prevalence

Front 5

Population is measured for prevalence of the disease at a specific point in time. What type of study?

Back 5

cross-sectional study (aka prevalence study)

Front 6

Study which compares one diagnostic test to the gold-standard?

Back 6

cross-sectional study (aka prevalence study)

Front 7

calculate sensitivity

Back 7

true positives divided by total with disease (a/a+c)

Front 8

calculate specificity

Back 8

true negatives divided by total without disease (d/d+b)

Front 9

How to remember how to get sensitivty and specificity off a 2x2 chart?

Back 9

sE is before sP in alphabet, so sEnsitivity is left column and sPecificity is right column

Front 10

SPIn

Back 10

positive test in a specific test rules in the disease

Front 11

SnNOut

Back 11

negative test in a sensitive test rules out the disease

Front 12

calculate Positive predictive value (PPV)

Back 12

true positives divided by total positive results (a/a+b)

Front 13

calculate Negative predicitve value (NPV)

Back 13

true negatives divided by total negative results (d/d+c)

Front 14

how to organize a 2x2 table

Back 14

outcome/disease is always on top

Front 15

when do you want a highly sensitive test?

Back 15

when you want to screen for a disease to rule it out (usually more false positives)

Front 16

low disease prevalence means what for PPV and NPV?

Back 16

PPV goes down and NPV goes up

Front 17

testing someone who has risk factors means what for PPV?

Back 17

PPV goes up (higher pre-test odds)

Front 18

calculate positive likelihood ratio (+LR); remember it's a ratio of likelihoods

Back 18

true positive probability/false positive probability (sens/1-spec)

Front 19

calculate negative likelihood ratio (-LR); remember it's a ratio of likelihoods

Back 19

false negative probability/true negative probability (1-sens/spec)

Front 20

how to remember how to calculate Likelihood Ratio? (where do you put the diseased population?)

Back 20

truly diseased population always goes on top of the calculation: for +LR, true positives are on top, for -LR, false negatives are on top

Front 21

when are exposures and outcomes in a prospective cohort study?

Back 21

exposure in the future, outcome further in the future

Front 22

when are exposures and outcomes in a retrospective cohort study?

Back 22

exposure in the past, outcome in the more recent past

Front 23

define the population of study in a cohort study

Back 23

those who don't have the outcome but who could all potentially experience that outcome

Front 24

define the population of study in a case control study

Back 24

those who have the outcome presently

Front 25

Cheapest type of study.

Back 25

cross sectional study

Front 26

when are exposures and outcomes in a case control study?

Back 26

study group is defined by presence of outcome; exposures are measured (past or present)

Front 27

Cohort study: what is measured?

Back 27

cOhort measures Outcomes in a group with similar exposures

Front 28

Case control study: what is measured?

Back 28

casE control measures Exposures in a group with similar outcomes

Front 29

Case Control studies cannot measure risk. Instead they measure what?

Back 29

Odds Ratio: how much more likely it is for a person with outcome is to have an exposure than a person without an outcome

Front 30

Define Absolute Risk (AR)

Back 30

incidence of outcome

Front 31

Define Relative Risk (RR)

Back 31

incidence of outcome in exposed/incidence of outcome in unexposed

Front 32

Define Attributable Risk (aka Absolute Risk Reduction or ARR)

Back 32

incidence of outcome in exposed - incidence of outcome in unexposed

Front 33

Define Relative Risk Reduction (RRR)

Back 33

1-RR

Front 34

Define Odds Ratio (OR)

Back 34

odds of exposure in person with outcome/odds of exposure in person without outcome

Front 35

Calculate Odds based on Probability

Back 35

Odds = probability of event/1-probability of event

Front 36

Calculate Probability based on Odds

Back 36

Probability = Odds/1+Odds

Front 37

Surgeon only operates on patients without significant comorbid conditions, then reports outcomes are better than other surgeons. What bias?

Back 37

selection bias

Front 38

Data gathered from 5 hospitals about stroke. One of the hospitals doesn't have MRI, so they use data from CT scans. What bias?

Back 38

measurement bias

Front 39

Study finds that construction workers who work 60 hours or more per week are more likely to have skin cancer. They conclude being over-worked causes skin cancer. What bias?

Back 39

confounding bias

Front 40

Patients with diarrhea are asked if they ate a specific food in the last week. Worry about what bias?

Back 40

recall bias

Front 41

New screening test claims to improve cancer survival by five years. Later study finds this cancer's average age of onset is earlier. What bias has this screening test created?

Back 41

lead-time bias

Front 42

Cancer prognosis is different in 2 hospitals. It is found that they use 2 different screeing test and one fails to catch the cancers with poor prognosis. What bias?

Back 42

length bias

Front 43

Type 1 (alpha) error vs Type 2 (beta) error: how to remember?

Back 43

Type 1: rejects the null
Type 2: don't reject null (remember TWO is a DOUBLE negative)

Front 44

Define p value

Back 44

probability that the differences found in the study occurred by chance

Front 45

How to increase Power in a study.

Back 45

increase number of subjects

Front 46

How to decrease the Confidence Interval in a study?

Back 46

increase number of subjects

Front 47

Conclusion of insignificant difference based on confidence interval? (2)

Back 47

it crosses 1 on plot of RR or Odds
it crosses 0 on plot of ARR