WEEK 7: COHORT, CASE CONTROL STUDIES

Question 1

what are cohort studies

Answer 1

Involve the formation of a cohort, which is a group of individuals followed over time

Question 2

points to a cohort study

Answer 2

• More expensive, time consuming
• Not efficient for diseases with long latent periods
• Better exposure and cofounder data
• Less vulnerable to information bias

Question 3

retrospective cohort study

Answer 3

A retrospective cohort study looks back in time. It uses preexisting secondary research data to examine the relationship between an exposure and an outcome. Data is collected after the outcome you’re studying has already occurred
- cheaper, faster
- more vulnerable to bias

Question 4

prospective cohort study

Answer 4

a prospective cohort study follows a group of individuals over time.
- starts at the cohort

Question 5

Incidence (Rate) Ratio - Relative Risk in Cohort Studies

Answer 5

Comparison of the incidence of a characteristic in 2 independent populations (or independent subpopulations) calculated by taking a ratio of their incidence rates
- exposed vs. unexposed

Question 6

advantages of cohort studies

Answer 6

• Valuable when exposure is rare
• Can examine multiple effects of a single exposure
• Easier to determine the temporal relationship b/w exposure and outcome
• Allows measurement of incidence

Question 7

incidence

Answer 7

the # of new cases of disease in a population during a specified period of time
Reported in terms of incide rate or an incidence population

Question 8

formula of odds ratio

Answer 8

(odds of disease in exposed/odds of disease in unexposed)

Question 9

2 necessary requirements for selection of controls

Answer 9

1. controls must come from the same source population as cases
2. controls must be selected independently of exposure

Question 10

population based control

Answer 10

control selected from the general population, most suitable when cases are from well-defined geographic areas

Question 11

nested controls

Answer 11

controls selected from an existing cohort population. Controls represent a subset of the full source population

Question 12

hospital/clinic based controls

Answer 12

controls selected from among patients at a hospital or clinic

Question 13

case control studies advantages

Answer 13

• More efficient than a cohort study (in terms of time, money, and effort)
• Suited to diseases with long latent period
• Optimal for rare disease
• Can examine multiple exposures

Question 14

disadvantages of case control studies

Answer 14

• Exposure is assess after development of the outcome
  May be unsure about temporal sequence b/w exposure and disease
  Recall bias
• Prone to selection bias in control choice - especially if response rates are low
• Can only study 1 disease or outcome
• Inefficient for rare exposures
• Can NOT calculate aboke measure of association

Question 15

individual vs frequency matching

Answer 15

Individual matching - performed participant by participant
Frequency matching - providing similar distributions of confounders in groups

Question 16

what is censoring

Answer 16

occurs when participants in a prospective vs longitudinal study die, drop out, are lost to follow-up, or are removed from further analysis

Question 17

Population Attributable Risk Percentage (PAR%)

Answer 17

the proportion of incident cases in the total population that can be attributed to some people having the exposure

Question 18

what is the rate difference

Answer 18

absolute difference in the incidence rate b/w the exposed group and the unexposed group (also called excess Rise, Attributable Risk, + isk difference)
Ex. if 10% of the unexposed and 15% of the exposed became ill during the study period, the excess risk in the exposed was 15%-10% = 5%

Question 19

what is a proportion

Answer 19

• a ratio in which the numerator is a subset of the denominator (such as the denominator consisting of all study participants and the numerator including only females over 60 yrs of age)

Question 20

what is loss to follow up

Answer 20

the inability to continue tracking a participant in a prospective or longitudinal study bc the person drops out, relocates, or dies or stops responding

Question 21

what is a case control study

Answer 21

study that compares the exposure histories of people with disease (cases) and people w/out disease (controls)

Question 22

what is a case

Answer 22

study participant with the infectious or parasitic disease, non-communicable diseases, neuropsychiatric conditions, injury, or other disease, disorder, disability, or health condition of interest to the researcher

Question 23

what are the 3 options for matching

Answer 23

1. No matching
2. Frequency (group) matching
3. Matched pairs (individual) matching

Question 24

measures of association

Answer 24

refers to a # that summarizes the relationship b/w an exposure and a disease outcome

Question 25

what is the measure of association for case control studies

Answer 25

odds ratio

Question 26

what is a fixed population

Answer 26

all participants start the study at the same time and no additional participants are added after the studies start date

Question 27

incidence rate

Answer 27

the # of new cases of disease in a population during a specified period of time divided by the total number of people in the population who were at risk during that period
- sometimes called the absolute risk

Question 28

Cumulative Incidence/Incidence Proportion

Answer 28

the % of people at risk in a population who develop new disease during a specific period of time