Analytical Studies: case-control Studies Flashcards
Purpose of Epidemiology
To _________ community health problems
To identify the ________ and ______ of disease
To plan and evaluate health services
diagnose
natural history; aetiology
Strategies in Epidemiology
Epidemiologic __________
Epidemiologic ____________
surveillance
research
Epidemiological study designs is divided into 2
List them
Observational
Experimental
Observational Epidemiological study designs is divided into 2
List them
Descriptive
Analytic
Observational Studies
Investigator observes the __________________ (a “_________ experiment”).
Documents __________ and __________
Documents who does or does not _________________
natural course of events
natural; who is exposed
who is non- exposed
develop the outcome of interest
Case series
Descriptive or Analytical?
Descriptive
Cross sectional
Descriptive or Analytical?
Descriptive
Correlational
Descriptive or Analytical?
Descriptive
Case-control
Descriptive or Analytical?
Analytical
Cohort
Descriptive or Analytical?
Analytical
Clinical trials
Descriptive or Analytical?
Analytical
Descriptive Studies
______________________________ of the distribution of a disease, such as ___,____,_____
Describe the general characteristics
Person Place Time
Importance of Descriptive Epidemiology
Assess disease _______
Determine presence of an ________
___________ generation
Guide design of ___________
Guide policy
trends
epidemic
Hypothesis
analytical studies
Case Reports and Cases Series
__________ of a single patient or a series of patients
Difficult to differentiate between various alternative explanations
Represent ________ in the identification of new diseases or adverse effects of exposures
Detailed report
first clues
Most basic type of a descriptive study of individuals are ??
Case reports and Case series
Correlational studies
Use data from entire populations to ______________ between _________ during _______ period of time or __________ at _______ points in time
compare disease frequency
different groups ; the same
in the same population; different
Correlational studies
Advantages: useful for the __________
Disadvantages: based on _______ and may __________, inability to ______________ at individual level
formulation of hypotheses
averages; miss contributing factors
link exposure with disease
Presence or absence of correlation implies valid statistical association
T/F
F
Presence or absence of correlation does not imply valid statistical association
Cross Sectional Surveys
Presence or absence of _____________ is assessed at _________ point in time
Provide “ ________ ” of health experience
both exposure and disease
the same
snapshot
________ provides a snapshot of healtg experience
Cross sectional surveys
Cross sectional surveys
Disadvantage: _________ relationship of exposure and disease is not always _________
Temporal
distinguishable
So why proceed to an analytical study?
Often when we need to answer the following type questions:
What is the ___________ for an outbreak of diarrhoeal disease?
What are the _______ for neonatal tetanus?
What ______ are associated with increased mortality for persons with measles?
Does smoking cause lung cancer?
source of infection
risk factors
factors
Analytical epidemiology
Done in order to find out if ______________________________
It Attempts to provide the ____? and _____? of health related events.
an outcome is related to an exposure.
why; how
Analytical epidemiology
May take the form of
-__________ surveys , where the researcher makes _______ on the population)
- ___________/________ surveys (_________ on the population,
observational; no influence
interventional; experimental
some influence
Analytical epidemiology
May take the form of
- observational surveys e.g ________ studies, ______ studies
- interventional/experimental surveys e.g, in ______ drugs are given)
case-control
cohort
clinical trials
Case-control studies
Aetiologic studies in which comparisons are made between individuals.
Individuals who have a disease (____)
Vs
individuals who do not have the disease (______)
cases
controls
Major Steps in a case-control study
Define and select _____
Select _______
Do __________
Ascertain ————-
_______ analysis and ____ measurement
If exposure is more in cases than in controls then ____________ is suspected
Test any differences for ______ significance
cases; controls; Matching
exposures; Comparison; risk
causal association
statistical
In creating a case-control study,
Ascertain exposures: Enquiry and record verification for the ________ in both groups
Comparison analysis and risk measurement: ____________ in cases and controls
amount of exposure
Compare exposure
Selection of cases
Study begins with cases, i.e. the patients in whom ________________________.
all the details of ______________________ are obtained
usually new cases (______ cases) will be chosen either from the ____________ or ___________.
the new cases, which are (similar or different?) clinically, histologically, pathologically and in their duration of exposure (———-) will be chosen to avoid any error and for better comparison.
care in selection of cases is given importance while selecting them to avoid errors in comparison and analysis
the disease has already occurred.
their exposure to the suspected cause/causes
incident; general population or from hospitals
Similar; stage
Sources of cases
Cases may be chosen either from
•______________ (hospital)
•From —————
A single source
multiple sources.
What is a control??
A control is as like a case as is possible except that ________________
They must have the same ______________ as a case and must be subject to the same _________ and ________ criteria.
they do not have the disease (outcome) in question.
opportunity for exposure
inclusion and exclusion
In selecting a control, one control group is optimal for all situations
T/F
F
No one control group is optimal for all situations
There must be scientific, economic and practical considerations in the selection of controls
T/F
T
Principles of Control Selection
From (same or different?) study base (target population) as cases
Selected (dependent or independently?) of exposure status!!
If they had developed illness, they would have been a case
“Like should be compared with the like”
Same; independently
Control should have Comparable information to cases
T/F
T
Sources for controls
Controls may be obtained either from
•_________
• ________
• ________(———- preferred if available) or
• ________.
General population
Hospitals
Relatives; twins
Neighbors
General Population Controls
Advantages
– If _______ in general population known – direct __________
Disadvantages
– ______
– ________
all cases
calculation of risk
Cost; Sampling frame
Neighborhood Controls
Advantages:
– _________ , efficient
– _______ for potentially confounding variables
Disadvantages
– _______ related to neighborhood
– Potential _____
Inexpensive; Matched
Exposure; bias
Hospital Controls
Advantages:
– _______
– Come from __________
Disadvantages:
– Control disease may be __________
– Hospitalized controls differ from ___________
Convenient; same catchment area
linked to exposure
general population
Relatives/Friend Controls
Advantages – _______
Disadvantages
–_____
– Friends may share ________
Convenient
Bias; same exposure
Matching is a comparative technique of ____________________ present in cases and controls, except ______________
neutralizing all other variables
the variable (disease) under study
Purpose of matching is to eliminate ___________ (______) while conducting the study.
systematic errors
biases
Limitations of matching
By matching, we can match only the _________________ like __________
Cannot match the ______________ playing a role in causation.
known confounding variables like age, sex, occupation etc
unknown confounders
Enquiry about exposure
Done ((before or after?) the cases and controls are _______ to the maximum possible extent.
Information is obtained in both groups in a similar manner.
Also involves searching the available records with regard to the exposure to the suspected cause and its duration.
After ; matched
Biases
__________, or deviation of results or inferences from the truth may arise at any point in the course of study or throughout due to chance.
Systematic errors
_________ bias is the commonest error usually committed.
Selection
Selection bias
Either __________ (to some extent) or ____________ or both can minimize it.
matching
randomization
Confounding due to bias
A confounding variable is A variable which is capable of ____________________
And is also capable of ____________________________.
Allowing ___________________ is confounding bias
causing the effect or disease directly on its own
causing the effect or disease indirectly with the association of another factor
this variable into the study
Examples for confounding bias
Usually the presence of confounders leads to ____________ e.g. Goitre is seen mostly at high altitudes, but actually, the iodine deficiency at high altitudes is the cause of goitre there.
Similarly, alcoholism is suspected to be the cause of liver cancer but the smoking, which is usually associated with alcoholism may be the confounding variable causing the disease
indirect causal associations
Examples for confounding bias
_____ is the best
Age
Information bias
Any error in ____________ i.e. Data about cause will lead to the false inference or results.
This bias is very frequently seen in ___________ studies, as the entire process involved is mostly __________ verification.
collecting information
case-control
subjective
Memory bias or Recall bias
This is the inability on the part of an individual (case or control) to _____________________
Similarly, patients may ________________ to please the investigator.
recollect things that happened in the past accurately.
give wrong information or exaggerate
Interviewing bias
Errors can occur while collecting data by interviewing, if the interviewing techniques are ____________ and _________ in a similar fashion and for similar duration for all the cases and controls.
not standardized and applied
Investigator bias
This is (occasionally or frequently ?) encountered, usually an (intentional or unintentional?) one.
The investigator may conduct interview with one case or a control for a longer time and another for a short time.
The interviewer’s ideas and feelings may unintentionally influence responses while interviewing due to over enthusiasm.
occasionally; unintentional
Measurement bias
Errors usually occur while ___________ the __________ or ___________.
Measurement bias will occur if measurements are _______________ using similar techniques or methods both in cases and controls.
measuring the exposure factor or the suspected cause
not taken in a similar manner
Analysis in case-control studies
rates
proportions of exposure
Analysis for risk measurement
The proportion of the cause in
•the cases (_______)
and in
• the controls (_______)
Are measured.
a/a+c
b /b+d
________ rates only can be directly calculated from the case-control study design, but not the _____ rates or ________
Exposure
incidence
relative risk (RR).
Odds ratio aka ____________ ratio (___/_____)
also assesses the risk
Cross-product
ad/bc
In _____ diseases with (low or high?) incidence, OR is equally as useful as ______
Given that ____ can not be derived from case- control studies.
rare ; low
RR
RR
Intuitively….
If the frequency of exposure is higher among the cases than the controls,
then the incidence will probably be higher among the ______ than the _______
exposed
non-exposed.
Strengths of case-control Studies
Useful in ____ diseases with ____ incidence
_____ exposures
(Slow or Rapid?) ,_______ period
(Small or Large?) sample size
No need for ______
Low cost
No ethical issues
Rare;low
Multiple; rapid; no latency
Small; follow up
Limitations of case-control Studies
No calculation of _____ and ____
Selection of _____ is difficult
Not suitable for rare _______
Problems with _______
rates and risks
controls; exposures
mass significance
Limitations of case-control Studies
____________________ (main weakness) .
The reliability of the study depends on the ____________.
Problems with recall
Data is collected _________, therefore they are relatively unreliable.
Looks at only one outcome
choice of controls
retrospectively
