Lecture 2

Question 1

prevalence formula

Answer 1

# people who have disease at given point in time
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
# of people in population of interest

Question 2

cumulative incidence formula

Answer 2

# new cases of disease in a given time period 
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
# people who can develop that disease

Question 3

prevalence in relation to incidence and duration

Answer 3

prevalence = indidence x average duration

Question 4

prevalence

Answer 4

• the probability of having a disease at at given point in time
• the pre-test probability
• how common a disease is
• gives you baseline probability

Question 5

incidence

Answer 5

• the proportion of new cases of disease in the population at risk of getting the disease over a given period of time
• also known as risk
• tells you about what could happen in the future

Question 6

incidence versus prevalence

Answer 6

• incidence based on new cases
• prevalence based on new and old
• incidence based on cases that develop over a specified period of time
• prevalence is based on cases that exist at a single point in time

Question 7

incidence density

Answer 7

• the number of new cases of disease that develop over a given time period divided by person-time at risk of disease

Question 8

if incidence increases and average duration remains the same

Answer 8

• prevalence increases

Question 9

if average duration of a disease increases and incidence stays the same

Answer 9

• prevalence increases

Question 10

attack rate

Answer 10

• the proportion of people who develop the disease, among those at risk, during a specified time period

Question 11

attack rate formula

Answer 11

new cases of disease in a given time period
___________________________________
persons at risk

Question 12

case fatality rate

Answer 12

• the proportion of people affected with a disease who die from it, in a given time period

Question 13

case fatality rate formula

Answer 13

deaths from a disease in a given time period
____________________________________
number of persons who have that disease

Question 14

mortality rate

Answer 14

• the proportion of people who die, among those at risk of death, in a given time period

Question 15

mortality rate formula

Answer 15

deaths in a given time period
__________________________
population at risk of dying

Question 16

how to get estimates of pre-test probability?

Answer 16

• knowledge of prevalence in your clinical site
• medical literature
• clinical predictions
• clinical experience

Question 17

test threshold

Answer 17

• separates “don’t test, don’t treat” zone from “test” zone

Question 18

treat threshold

Answer 18

• separates “test” zone from “don’t test, treat” zone

Question 19

determines where the thresholds are set

Answer 19

• accuracy of test
• risk of test
• seriousness of illness and benefit of treatment
• risk of treatment

Question 20

accuracy of test

Answer 20

• test threshold will be lower for more accurate tests

Question 21

risk of test

Answer 21

• test threshold will be higher for more risker; invasive tests

Question 22

seriousness of illness and benefit of treatment

Answer 22

• test and treatment thresholds will be lower for serious illnesses with beneficial treatment

Question 23

risk of treatment

Answer 23

• treatment threshold will be higher for riskier treatment

Question 24

if pre-test probability is below test threshold

Answer 24

• not wise to test for the condition at all because a positive test is more likely to be a false positive than a true positive

Question 25

rule in

Answer 25

- moved above treat threshold

Question 26

rule out

Answer 26

- moved below test threshold

Question 27

if pre-test probability is above the treat threshold

Answer 27

- don't test, just treat

Question 28

pattern recognition

Answer 28

- one of the most efficient diagnostic strategies used by seasoned clinicians

Question 29

point prevalence

Answer 29

- measured at a single point in time for each person

Question 30

period prevalence

Answer 30

- describes cases that were present at any tine during a specified period of time

Question 31

another name for prevalence studies

Answer 31

- cross-sectional studies | - people are studied at a "cross-section" of time

Question 32

cohort

Answer 32

- population under examination in an incidence study - group of people having something in common when they are first assembled and are then followed over time for the development of outcome events

Question 33

another name for incidence studies

Answer 33

- cohort studies

Question 34

cumulative incidence

Answer 34

- describe the rate of new events in a group of people of fixed size, all members of which are observed over a period of time. - new cases are accumulated over time

Question 35

incidence density

Answer 35

- to measure the number of new cases emerging in an ever-changing population, one in which individuals are under study and susceptible for varying lengths of time. - common for clinical trial companies

Question 36

denominator of incidence density measure

Answer 36

- person-time

Question 37

dynamic populations

Answer 37

- those in which some individuals in the population are entering and others leaving as time passes