Epidemiological study designs:analytical studies Flashcards
Epidemiological study designs are divided into two name them
Descriptive Studies
•B. Analytic Studies
What kind of studies are done under descriptive and analytical studies (observational and experimental as well and give examples under each)
Types of studies under cohort studies as well
Descriptive Studies
- Case Reports
- Ecologic or Correlational Studies
- Cross-sectional studies
Analytic Studies
1. Observational •Cross-sectional studies(there’s analytical work done to see the relationship between determinants and diseases •Case control studies •Cohort studies •Prospective •Retrospective •Nested Case Control Studies
- Experimental
•Clinical Trials
•includes community based interventions
What are case reports
What three things do they show?
What are they used for?
Name two advantages and disadvantages of case reports
An article that describes and interprets an individual case, often written in the form of a detailed story.
•
Cases that show an important variation of a disease or condition
•Cases that show unexpected events that may yield new or useful information
•Cases in which one patient has two or more unexpected diseases or disorders
•
Primary use is for initial description of a “new” disease or phenomenon
•May be hypothesis generating
•
Advantages
•May be quick and inexpensive to perform
•“Easy” publications for trainees
Disadvantages
•Measures only the frequency of occurrence of associated symptoms, signs, exposures, etc.
•There is no comparison group and no possible measure of association
•without comparison, you have no basis to estimate whether the
occurrence of a particular finding is exceptionally common, etc.
- Frequently data based on chart review;
- data collected are not standardized
- missing information may be considered as not present, rather than not evaluated
What are ecological or correlational study
What is the unit of analysis in this study
What two things differentiates ecological study from other epidemiological studies
Give an example
Examines the rates of disease in relation to a factor described on a population level
•The unit of analysis are populations or groups of people rather than individuals
•Two key things that distinguish a traditional ecologic study from other types of epidemiologic studies are:
•1. the population unit of analysis
•2. an exposure status that is the property of the population
•Eg researchers conducted an ecologic study with groups identified by place to determine the association between air pollution and mortality rates
•Study to examine the association between drinking chlorinated water and birth defects
Hypothesis is generated in ecological studies
State the advantages and disadvantages of these kind of studies
What is an ecological fallacy?
Ecological or correlational Studies •Hypothesis generating •Advantages •Typically uses information that is readily available (census data, mortality data, etc.) •Inexpensive •
Disadvantages
•Lack of linkage between individuals and exposures/outcomes
•Ecologic Fallacy
= an association observed between variables on an aggregate level does not necessarily represent the association that exists at the individual level eg. Study to examine the association between drinking chlorinated water and birth defects or
tendency to draw conclusions on the individual level based on the observations from the aggregate level.
What is the measure of frequency and measure of association in cross sectional studies
Principal measurements: •Exposure(contact with something or anything that can lead to a disease or protect you From a disease)and outcome at the same time (snap shot)(using questionnaire) •Measure of frequency: Prevalence •Measures of association: •Prevalence odds ratio •Prevalence ratio (relative prevalence)
How is a cross sectional study designed
Define your population
Gather data on exposure and disease
Group the data into four groups
Exposed and have the disease or exposed and do not have the disease
Not exposed but have the disease or Not exposed and do not have the disease
Disease or no disease is vertical
Exposed or not exposed is horizontal
How is a cross sectional study analyzed( by stating the prevalence of exposure in people with the disease and people who don’t have the disease and stating the prevalence of the disease in exposed compared to not exposed )
Exposed = people with th disease plus people without the disease(a+b)
Not exposed= people w disease plus people without disease(c+d)
People w disease= people exposed plus people not exposed (a+c)
People without disease= people exposed plus people not exposed(b+d)
Before all this draw the 2by 2 table and Input the values so you don’t confuse yourself
Please
Prevalence of exposed in people with disease(a), then you find value for people with disease (a+c)
Is a divided by a+c
Vs.
Prevalence of exposed in people without the disease(b) , then you find value of people without the disease
b divided by b+d
Prevalence of disease in exposed is prevalence of the disease(a) then you find the value of those exposed(a+b)
a divided by a+b
Vs.
Prevalence of people having the disease but we’re not exposed is (c) then you find the value of those not exposed(c+d)
Name five advantages and disadvantages
of epidemiological study designs
Advantages:
•Relatively short time period
•Relatively inexpensive
•Estimates the disease burden
•May simultaneously investigate several exposure/outcome relationships
•If disease is persistent, the prevalence ratio may estimate the risk ratio.
Disadvantages:
•Difficult to estimate the timing of the exposure-outcome relationship, unless the exposure is permanent
- Bias of exposure measurements possible, especially if historical (recalled)
- !” “survivor” bias - persons with severe exposure may die more quickly, would not be included in assessment of prevalent cases of disease
- Typically cannot estimate risk ratio
Name five uses of cross sectional studies
Used primarily to determine the prevalence of outcomes of interest
- Used to determine the burden of disease
- Assesses associations between exposures and outcomes at the same time
- Helps to provide useful questions for further studies
- REVIEW OF SELF-REPORTED ADHERENCE TO DIET ARTICLE
Name three examples of case control studies ,define cases and controls,the traditional view,the modern view,state which view is used in case control studies
What is control group and state it’s purpose
In case control, Investigators obtain and compare the exposure histories of cases and controls true or false
Case-control studies:
•case-referent, case-comparison, TROHOC
- Traditional view:
- Subjects in case control studies are selected on the basis of whether they have or do not have the disease.
•Those that have the disease are termed cases and those who don not have the disease are termed controls
Cases and controls are picked from different groups
Modern View:
•It is a method of sampling a population in which cases of disease are identified and enrolled and a sample of the source population that gave rise to the cases is also identified and enrolled
Cases and controls are taken from same group
Modern view is used
The sample of the source population is known as the control group
- Its purpose is to provide information on the exposure distribution in the population that produced the cases, so that the disease rates in exposed and non-exposed can be compared
- This answers the question: if this control subjects would have become a case in this study, would they have been included in the case population?
What is trohoc?
Opposite of cohort
We know the disease but go back to find the contact
Which type of study does the investigator determine the outcome but not exposure?
Which study does the investigator determine the exposure not the outcome
In cross sectional study it is difficult estimating the timing of the exposure and outcome cuz the person doesn’t have the disease anymore but had it sometime ago and was exposed sometime ago true or false
Case control
Cohort
True
What is the principal measurement of case control and the measure of association
Principal measurements:
•Exposure(s)
•Measures of association:
•Odds ratio
How do you define a case
Name three sources of cases
CASES
•Case definition
•Part of the definition is classic epidemiology
•Person, Place, and Time
•Also include diagnostic tests, clinical and pathological exams etc.
•Use as much information as is available
•Source of cases
•Hospitals, population based, disease registry
How are cases selected
Define our cases
•Workers in factories who develop leukemia (or developed leukemia if retrospective) over the 20-year period
•Take a sample of cases (or enroll all cases if possible)
How are controls selected ,state the difference between hospitalized controls and population controls , in a selecting a control from the hospital what are you supposed to look out for? In selecting a control from the population what are you to look out for?
state the difference between cohort study and case control study with respect to control
A sample of the source population that gave rise to the cases
The would criterion
•The source population is a group whose members would end up as a case in the study if they developed the disease
Hospitalized controls
•Must make sure that the condition for which they are in the hospital has no relationship with the disease or exposure of interest
•The illness in the control group should have a similar referral pattern to the disease you are studying example- if Ure doing a study on hypertension don’t pick controls with diabetes cuz hypertension and diabetes have similar risk factors
•
Population Controls
•More generalizable
•Likely the same source population that gave rise to cases
•Time consuming, less interest to participate, recall bias
In a cohort study you are following this source population until they develop disease
•In a case-control study, you sample this population to assess the exposure distribution in the population
