Analytical Studies: case-control Studies Flashcards by Iseoluwa Ojo

Purpose of Epidemiology

To _________ community health problems

To identify the ________ and ______ of disease

To plan and evaluate health services

diagnose

natural history; aetiology

How well did you know this?

Not at all

Perfectly

Strategies in Epidemiology

Epidemiologic __________
Epidemiologic ____________

surveillance

research

How well did you know this?

Not at all

Perfectly

Epidemiological study designs is divided into 2

List them

Observational
Experimental

How well did you know this?

Not at all

Perfectly

Observational Epidemiological study designs is divided into 2

List them

Descriptive

Analytic

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Case series

Descriptive or Analytical?

Descriptive

How well did you know this?

Not at all

Perfectly

Cross sectional

Descriptive or Analytical?

Descriptive

How well did you know this?

Not at all

Perfectly

Correlational

Descriptive or Analytical?

Descriptive

How well did you know this?

Not at all

Perfectly

Case-control

Descriptive or Analytical?

Analytical

How well did you know this?

Not at all

Perfectly

Cohort

Descriptive or Analytical?

Analytical

How well did you know this?

Not at all

Perfectly

Clinical trials

Descriptive or Analytical?

Analytical

How well did you know this?

Not at all

Perfectly

Descriptive Studies
______________________________ of the distribution of a disease, such as ___,____,_____

Describe the general characteristics

Person Place Time

How well did you know this?

Not at all

Perfectly

Importance of Descriptive Epidemiology

Assess disease _______

Determine presence of an ________

___________ generation

Guide design of ___________

Guide policy

trends

epidemic

Hypothesis

analytical studies

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Most basic type of a descriptive study of individuals are ??

Case reports and Case series

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Presence or absence of correlation implies valid statistical association

T/F

F
Presence or absence of correlation does not imply valid statistical association

How well did you know this?

Not at all

Perfectly

Cross Sectional Surveys

Presence or absence of _____________ is assessed at _________ point in time

Provide “ ________ ” of health experience

both exposure and disease

the same

snapshot

How well did you know this?

Not at all

Perfectly

________ provides a snapshot of healtg experience

Cross sectional surveys

How well did you know this?

Not at all

Perfectly

Cross sectional surveys

Disadvantage: _________ relationship of exposure and disease is not always _________

Temporal

distinguishable

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

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

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 No calculation of _______ Involves calculation of ________

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