Epidemiology 10.1-case-control studies and other study designs Flashcards
What is ecolgic study ? how do you study population level?
Ecologic study
Descriptive studies of how to categorize communities by exposure and outcome
Population level
•ecologic, aggregate or correlational studies
What is an ecologic study ?
To include crude explorations of exposure and disease in which the group (total population, community) is the unit of analysis
What are the stregths of an ecologic study ? what does it evulate ?
Strengths
- quick and inexpensive
- many populations can be studied
- Similar and different populations
- Evaluation of risk factors
- Sex, ethnic groups, socioeconomic status
How does Ecologic study get there information ?
Ecologic study
To use public data on group attributes and disease rates
•Surveillance systems
What are the limitations of a ecologic study ?
Ecologic study
Limitations
- Ecological fallacy
- Problems with potential confounding variables
- Limited information
- Population mobility (migration)
- Decrease the exposure
- Masking variable effects
What is ecological fallacy? What is the problem ?
Ecological fallacy
- Association between disease and group attributes may not signify the same association at the individual level
- Cannot link individual risk with disease causality
What is a case report ? What is it used for ?
Case report
- Detailed report by one or more clinicians of the medical history of a patient.
- Unusual medical histories
- Identification of a new disease or adverse exposures
What are the limiations of a case report ?
Case report
- Limitations
- We cannot used a measure of association
- Chance(oneperson)
- Nocomparisongroup
What is case series ? how long does it occur ? What is it used for ?
Case series
- Description of the characteristics of a group of patients with that disease.
- Usually occur within a short period of time
- Possible outbreaks
- New diseases
ebola
What does a case series lack ?
Case series
We cannot used a measure of association
•No comparison group
What is a cross sectional study or prevelance study ? What does it do ? How are exposure and dieases determined ? Cases of the diease are ? And what dont we know ?
Cross sectional study or Prevalence study
- Survey a population
- Exposure and disease are determined simultaneously for each participant
- Cases of disease are prevalent cases
–Do not know the duration of disease
Gordis,
What is are the three things cross sectional study used for ?
Cross sectional study
- To define a population
- To determine the presence or absence of exposure for each participant
- To determine the presence or absence of disease for each participant
What is a cross sectional study used for ?
Cross sectional study
•To determine there is an association between exposure and disease
–To calculate the prevalence of disease in participants with exposure and compare it with the prevalence of disease in participants without the exposure
What is the formula for calcualte cross sectional study?
Cross sectional study
To calculate the prevalence of exposure in patients with disease and compare the prevalence of exposure in participants without the disease
What are the limitations of a cross sectional study ?
Limitations
–Prevalent cases
•Survival
–Not possible temporal relationship
•Simultaneous measures
What is needed to compare a study in case- control study ? What is not possible without a control ?
Case-control study
- To determine the significance of such observations in a group of cases, a comparison or control group is needed.
- The observations would have been intriguing, but no conclusion is possible without a control group.
What is the purpose of a case- control study ? Does it look at incidence or proportion ?
Case-control study
To evaluate the possible relationship of an exposure to a certain disease
–Cases (people with that disease)
–Controls (people without that disease)
•To determine that proportion of the cases were exposed and what proportion were not.
What is the first and second step in the case-control study ?
Case-control study
Gordis,
First step
–Selecting the cases (person with that disease)
–Selecting controls (persons without that disease)
•Second step
–To measure past exposure by interview and by review of medical records
How are case control and cohort study differnt ?
Case-control study
–Study begins with diseased and nondiseased people
•Cohort study
–Study begins with exposed and nonexposed people
Where can cases be selected from ?
Selection of cases & controls
•Cases can be selected from
–Hospitals
–Clinic patients
–Registries of patients
What is the problem from selecting cases from a single hospital ? What is the problem from getting cases from a tertiary care hospital ?
Problems with cases selected from a single hospital
–Results may not be generalizable to all patients with the disease
•Problems with cases from a tertiary care hospital
–Severely ill patients
What is incident cases? and what is the problem ?
Selection of cases & controls
Incident cases
–Newly diagnosed cases
–Problem with use of incident cases is that we must often wait for new cases to be diagnosed
What is prevalent cases ?
Selection of cases & controls
Prevalent cases
–Persons with the disease for some time
–Cases have already been diagnosed (larger number of cases)
–Survival
Why is a control so important ? Should the control be simialr to the case ? What must the control represent ?
Selection of cases & controls
Controls
–Is a major determinant of whether such a conclusion is valid
–Controls should be similar to the cases in all respects other than having the disease
–Representative of all persons without the disease in the population from which the cases are selected
