STUDY DESIGNS CHP400: Community Health Program- lI Mohamed M. B. Alnoor Research Methodology...

STUDY DESIGNS

CHP400:Community Health Program- lI

Mohamed M. B. Alnoor

Research Methodology

Observational / Descriptive Studies

Case reportCase series

Cross sectionalEcological

studies Present: Disease Past: Exposure

Cross - section Cohort

Case - control

Present:Disease & Exposure

Present: Exposure Future: Disease

nbmmb

Time is Key

CONTENT

Classification of Study Designs Observational Studies Observational / Descriptive Studies

o Case Reportso Case Serieso Cross-sectional studies (Health Survey)o Ecologic studies

STUDY DESIGNS

ExperimentalObservational

Animal

Experiment

HumanInterventio

nClinical trial

Analytical

Case control

Descriptive

Case report

Case series

Cross section

Ecological

Cohort


STUDY DESIGNSObservational / Descriptive StudiesCase Reports

Careful and detailed report by one or more clinicians of the profile of a single patient

•e.g. previously un-described disease•e.g. unexpected link between diseases•e.g. unexpected new therapeutic effect•e.g. adverse events


STUDY DESIGNSObservational / Descriptive Studies

o exposures (i.e. a case report gave the clue that “oral contraceptives” use increases

the risk of venous thromboembolism.

o “Luck” in being the first to encounter an interesting case. o Rigor in diagnosis, testing and documentation of clinical findings

Case Reports


STUDY DESIGNS

Strengths over one million case reports indexed on

Medline. uses language that is familiar to clinicians

and easy to interpret. useful reminder about conditions,

diagnoses etc. that are rarely seen in most practices.

for researchers, case reports generate hypotheses that can be tested using other study designs.


Observational / Descriptive StudiesCase Reports

STUDY DESIGNS

• No appropriate comparison group.• Cannot be used to test for presence of a

valid statistical association.• Since based on the experience of one

person:--- presence of any risk factor

may be purely coincidental

--- Not a true epidemiologic design.

Limitations:



STUDY DESIGNS

Limitations:

• Tendency to publish reports of strange conditions that have little relevance to

daily practice.• Some authors erroneously try to imply causation, therapeutic benefits, etc.



STUDY DESIGNS

Authors: Smart ER. Macleod RI. Lawrence CM.Title: Allergic reactions to rubber gloves in dental patients: report of three cases.Source: British Dental Journal. 172(12):445-7, 1992 Jun 20.


Abstract: Three cases of allergy to rubber are described. The patients exhibited peri-oral rashes following dental treatment by personnel wearing latex rubber gloves. Two of the patients were aware of possible allergy to domestic rubber products but did not reveal this as part of their medical history. With the increase in numbers of dentists wearing rubber gloves it is probable that there will be many more such cases reported in the future. Rubber products must then be added to the list of potential allergens which may be of some importance to the practice of dentistry.


STUDY DESIGNS

Experience of a group of patients with a similar diagnosis.

Cases may be identified from a single or multiple sources.

Generally report on new/unique condition. May be only realistic design for rare

disorders


Case SeriesObservational / Descriptive Studies

STUDY DESIGNS

• Useful for hypothesis generation.

• Used as an early means to identify the beginning or presence of an epidemic.

• Can suggest the emergence of a new disease (i.e. AIDS).

• Informative for very rare disease with few established risk factors.

Strengths:



STUDY DESIGNS

Limitations:

• Lack of an appropriate comparison group

• Cannot be used to test for presence of a valid statistical association

• Not a true epidemiologic design.



STUDY DESIGNSObservational / Descriptive StudiesCross-sectional studies

An “observational” design that surveys exposures and disease status at a single point in time (a cross-section of the population)

time

Study only exists at this point in time


STUDY DESIGNS

time

Study only exists at this point in time

Studypopulation

No Disease

Disease

factor present

factor absent

factor present

factor absent

Prevalence


Observational / Descriptive StudiesCross-sectional studies

STUDY DESIGNS

Often used to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions).

It measures prevalence, not incidence of disease.

Not suitable for studying rare or highly fatal diseases or a disease with short duration of expression.



STUDY DESIGNS

Strengths:

• Provides prevalence estimates of exposure and disease for a well-defined population.

• Easier to perform than studies that require follow-up (hence relatively inexpensive).

• Can evaluate multiple risk (and protective) factors and health outcomes at the same point in time.



STUDY DESIGNS

Strengths:

• May identify groups of persons at high or low risk of disease

• Can be used to generate hypotheses about associations between predictive factors and disease outcomes



STUDY DESIGNS

Limitations :

• Prevalent rather than incident (new) cases are used – the exposure could be associated with survival after disease occurrence, rather than development of the disease

• Temporal sequence between exposure and disease cannot be established

i.e. Which came first, chicken or the egg?



STUDY DESIGNS

Limitations :

•Usually don’t know when disease occurred.

•Rare events: a problem •Quickly emerging diseases: a problem



STUDY DESIGNS

Health Survey

Survey (n): Information gathered by asking a group of individuals the same questions related to their characteristics, attributes.

Survey (v): The process of collecting such

information



STUDY DESIGNS

Health Survey

Reach a large number of respondents; Generate standardized, quantifiable,

empirical data - as well as some qualitative data; and offers confidentiality / anonymity

A good survey has the potential to



STUDY DESIGNS

Health Survey

Surveys can be:

o Descriptive: These surveys do exactly what they

say - they describe. The goal is to get a snapshot - of your ‘respondents’

o Explanatory: These surveys go beyond description

and attempt to establish why things might be the way they are



STUDY DESIGNS

Health Survey

o Census: This is a survey that does not rely on a sample. A census surveys every single person in a defined or target population

o Cross-sectional surveys: This type of

survey uses a sample or cross-section of those respondents selected to represent a target population

Surveys can involve populations or samples of populations:



STUDY DESIGNS

Health Survey

Surveys administration :

o Face to faceo Telephoneo Self-administered.o Electronic e.g. E

mail



STUDY DESIGNS

Health Survey

o thorough planning,o meticulous instrument

construction,o comprehensive piloting,o deliberate execution,o and appropriate analysis

Conducting a survey capable of generating credible data requires:



STUDY DESIGNS

Health Survey

Survey questions can either be open or closed: :

o Open questions: Open questions can generate rich and candid data, but it can be data that is difficult to code and analyze.

o Closed questions: These questions force respondents to choose from a range of predetermined responses, and are generally easy to code and analyze statistically.



STUDY DESIGNS

Health Survey

Considerations in questionnaire Construction:

Providing clear background information and lucid instructions.

Logical organization. Comprehensive coverage without undue length. User friendly and aesthetically pleasing

layout and design.



STUDY DESIGNS

Ecologic studies

• Measures that represent characteristics of entire populations are used to describe disease and to postulate causal associations.

• Measure of interest is correlation between exposure rates and disease rates among different groups.

• Correlation coefficient (denoted as “r” )Range of “r” is from –1.0 to 1.0Revaluated in relation to difference

from 0.



STUDY DESIGNS

Ecologic studiesStrengths:• Cheap, quick, and simple (generally make use of secondary data)

Limitations:• Cannot link exposure-disease relationship at the individual level• Uses average exposure levels rather

than actual levels of exposure• Inability to control for confounding factors



STUDY DESIGNS

Ecologic studies Country A Country B

Person Salt Intake Hyp. Salt Intake Hyp. 1 1 Yes 1 Yes 2 1 Yes 1 Yes 3 1 Yes 1 No 4 3 No 1 No 5 3 No 1 No 6 3 No 2 No 7 3 No 2 No 8 5 No 2 No 9 5 No 2 No 10 5 No 2 No

Avg. 3.0 30% 1.5 20%

EXAMPLE: Country A: Country BPrevalence-Hypertension 30% 20%Average Salt Consumption Moderate Low



STUDY DESIGNS

Ecologic studies

The “Ecologic Fallacy”:

• Erroneous conclusions based on grouped data

• Patterns observed on the aggregate level are not observed on the individual level



STUDY DESIGNS


Observational / Descriptive StudiesSummary

Observational studies are the starting point. Case Reports, Case Series and Cross-sectional

studies are useful for generation of hypotheses. Cross-sectional studies:

-provide prevalence estimates of exposure and disease

-may identify groups of persons at high or low risk of disease

STUDY DESIGNS CHP400: Community Health Program- lI Mohamed M. B. Alnoor Research Methodology...

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