PHC 6001 Ch. 9 Case Control Studies
Case control study
• a solution to many cohort study limitations
• a study which cases of dz are identified, and then a sample of the population that
produced the cases is identified (controls)
-exposures are determined and compared for individuals in each group
desirable to conduct:
1. when exposure data are expensive or difficult to obtain (i.e. nested pesticide in
NHS)
2. When dz has long latent period (results may take decades to emerge; i.e. cancer,
CVD)
3. when dz is rare
4. when population is difficult to follow; high loss of follow up might bias results
5. when little is known about the dz; can evaluate many exposures (i.e. early studies
of AIDS)
source population of case control studies
consider hypothesis and person, place and time when defining
1. participants in an established cohort such as NHS
2. pregnant women delivering at BMC, 2014-2015
3. People eating at restaurant x from 9/1-9/30 2016.
4. Cape Cod, MA residents during 1980s
case definition
must have this to lead to accurate classification of disease
cases
can be identified from variety of places; efficient and accurate sources should be used
1. presenting to hospital or clinic
2. population registries (state cancer registries, notifiable infectious disease
registries)
-are the same as those that would be included in a cohort study
-are "statistically precious" - enroll as many as possible
, controls
a sample of the source population that produced the cases;
Purpose: to estimate the exposure distribution in source population that produced the
cases
Find -
1. nested from cohort population/study
2. population based
3. hospital or clinic
exposure prevalence
knowing the ___________ _________ among cases and controls is what allows us to measure
the association between an exposure and outcome
control selection
Two necessary requirements (really important)
1. Must come from the same source population as the cases - random selection is
necessary to obtain a representative sample of source population
(representativeness is a very important consideration)
2. Must be selected independently of exposure
would criterion
if the controls had experienced the outcome would they have been identified as cases in
your study?
nested controls
-selected from an existing cohort population; represent a subset of the full source
population
Example: studying pesticide exposure and risk of breast cancer in NHS cohort
Pros: come from *clearly defined source population that are already enrolled --->
"willing participants"
Cons: restricted to members of existing cohort and may limit hypothesis that can be
studied
population based controls
-selected from the general population, most suitable when cases are from well defined
geographic area
Sources: Random digit dialing, cell phone or internet subscribers, residence lists, tax lists,
voter registration lists, drivers license holders
Example: case control study of vit A and lung cancer. Cases come from massachusetts
cancer registry and controls come from the roster of registerd voters in massachusetts
Case control study
• a solution to many cohort study limitations
• a study which cases of dz are identified, and then a sample of the population that
produced the cases is identified (controls)
-exposures are determined and compared for individuals in each group
desirable to conduct:
1. when exposure data are expensive or difficult to obtain (i.e. nested pesticide in
NHS)
2. When dz has long latent period (results may take decades to emerge; i.e. cancer,
CVD)
3. when dz is rare
4. when population is difficult to follow; high loss of follow up might bias results
5. when little is known about the dz; can evaluate many exposures (i.e. early studies
of AIDS)
source population of case control studies
consider hypothesis and person, place and time when defining
1. participants in an established cohort such as NHS
2. pregnant women delivering at BMC, 2014-2015
3. People eating at restaurant x from 9/1-9/30 2016.
4. Cape Cod, MA residents during 1980s
case definition
must have this to lead to accurate classification of disease
cases
can be identified from variety of places; efficient and accurate sources should be used
1. presenting to hospital or clinic
2. population registries (state cancer registries, notifiable infectious disease
registries)
-are the same as those that would be included in a cohort study
-are "statistically precious" - enroll as many as possible
, controls
a sample of the source population that produced the cases;
Purpose: to estimate the exposure distribution in source population that produced the
cases
Find -
1. nested from cohort population/study
2. population based
3. hospital or clinic
exposure prevalence
knowing the ___________ _________ among cases and controls is what allows us to measure
the association between an exposure and outcome
control selection
Two necessary requirements (really important)
1. Must come from the same source population as the cases - random selection is
necessary to obtain a representative sample of source population
(representativeness is a very important consideration)
2. Must be selected independently of exposure
would criterion
if the controls had experienced the outcome would they have been identified as cases in
your study?
nested controls
-selected from an existing cohort population; represent a subset of the full source
population
Example: studying pesticide exposure and risk of breast cancer in NHS cohort
Pros: come from *clearly defined source population that are already enrolled --->
"willing participants"
Cons: restricted to members of existing cohort and may limit hypothesis that can be
studied
population based controls
-selected from the general population, most suitable when cases are from well defined
geographic area
Sources: Random digit dialing, cell phone or internet subscribers, residence lists, tax lists,
voter registration lists, drivers license holders
Example: case control study of vit A and lung cancer. Cases come from massachusetts
cancer registry and controls come from the roster of registerd voters in massachusetts
