Lecture 2, part 2

Question 1

What is an example of a case definition based on laboratory criteria?

Answer 1

Chlamydia
Isolation of C. trachomatis by culture
or
Demonstration of C. trachomatis in a clinical specimen by detection of antigen or nucleic acid

Question 2

What are case detection challenges in chlamydia?

Answer 2

Often asymptomatic, so lab detection for active infection depends on routine screening
Blood serology for antibodies
Testing tech changed over time to more sensitive tests, so have cases really gone up, or is it just better testing?
Cases more likely to be reported electronically

Question 3

Definition of population

Answer 3

A group of ppl with some common characteristic such as:
Age
Gender
Race/ethnicity
Place of residence
Workplace
School
Institution
In relation to a medical facility
Occurrence of a life event

Question 4

An investigation can focus on what?

Answer 4

Either on the entire pop, or just a subset of that pop
-Generalize back to the larger group

Question 5

What pop is the pop for which you would like to make conclusions?

Answer 5

Target pop

Question 6

Definition of fixed pops

Answer 6

Membership is relatively permanent and often defined by a singular event
-Once a person experiences the event, they remain part of the pop for life

Question 7

Exs of fixed pops

Answer 7

Atomic bomb survivors
Vets of Vietnam war
Birth cohorts
Enrollment in a study

Question 8

Definition of dynamic pops

Answer 8

Membership is transient and defined by current status
-Person is a member only as long as they meet the definition of the pop
-Ppl cease to be members when they no longer meet the definition

Question 9

Exs of dynamic pops

Answer 9

Residents of the city of Boston
Professional football players
Women who have given birth within the past 12 mos

Question 10

Time is a _____ ______ based on the question being studied

Answer 10

relative unit

Question 11

What are the various methods of counting time?

Answer 11

Calendar time (minutes, hours, days)
Period or point in life (ex: birth, age range)
Relation to external events

Question 12

For time you need what two things?

Answer 12

A beginning and an end

Question 13

Time is often _____, depending on the study

Answer 13

arbitrary

Question 14

Definition of ratios

Answer 14

A fraction of two mutually exclusive groups

Question 15

Characteristics of ratios

Answer 15

Used mostly as an effect parameter
Mostly descriptive
Has the form A/B
Numerator is unrelated to the denominator
Does not imply any particular relationship btwn A and B
Ranges from 0 to infinity

Question 16

Definition of proportion

Answer 16

Type of ratio that relates a part to a whole

Question 17

Characteristics of proportions

Answer 17

Used to describe the composition of a whole/descriptive measure
Numerator is a subset of the denominator
A/(A + B)
Often expressed as a percentage
Ranges from 0 to 1

Question 18

Definition of rate

Answer 18

Measures the speed at which events occur in a given pop over a specified period of time (velocity)

Question 19

Characteristics of rates

Answer 19

Used to compare frequency of events in different pops, places, or times
Numerator = # of events
Denominator = pop at risk for the event
Dimension of 1/time
Ranges from 0 to infinity

Question 20

Definition of prevalence

Answer 20

A measure of the proportion of ppl in a pop who have a dz at a specific point in time, the existing burden of dz

Question 21

What is the purpose of prevalence?

Answer 21

Provides a snapshot of dz in the pop

Question 22

What are common measures of prevalence?

Answer 22

Point prevalence
Period prevalence

Question 23

Definition of incidence

Answer 23

The number of new cases of dz that occur during a specified period of time in a pop at risk for developing the dz

Question 24

Purpose of incidence

Answer 24

Provides idea of how quickly new cases are occurring

Question 25

Common measures of incidence

Answer 25

Incidence rate
Cumulative incidence