EPIDEMIOLOGICAL

STUDY METHODS

OKETADE SOA

OUTLINE• INTRODUCTION• DEFINITIONS• CLASSIFICATION• STUDY DESIGNS • VARIOUS DESIGNS• CONCLUSION

• INTRODUCTION• The science of epidemiology has matured

significantly from the times of Hippocrates and john snow [physician] that the techniques for analysing data vary depending on the type of dxs being monitored but each study will have similarities. environmental factors can influence the occurrence of the diseases.

epidemiology study of what is upon the peopleDerived from the greek terms epi=upon,among.

demos=people, district. Logos study, word.

DEFINITION OF EPIDEMIOLOGY

• Epidemiology is the study of distribution and determinant of health related state or event in a specified human population and the application of this study to the control of health problem.

EPIDEMIOLOGY [DEFINITION OF KEY TERMS]

• Distribution : Frequency (including rates & risks) & pattern of health events(person, place, time)

• Determinants : factors or events that are capable of bringing about a change in health

• Human population : Epidemiology examines health events among population groups rather than individuals.

EPIDEMIOLOGY [DEFINITION OF KEY TERMS]

• Health related states: infections, chronic diseases & physiological events &various states of health such as disability, injury, mortality

• Health related events : immunization, hospital attendance, bed occupancy

• Application : basis for directing interventions

CLASSIFICATION

CLASSIFICATION(CONT.)

CORRELATIONAL

OBSERVATIONAL VS EXPERIMENTAL STUDIES

• Observational studiesAllow nature to take its cause; the investigator measures but does not intervene

• Descriptive study: focuses on the description of the occurrence of a disease in a population

• Analytical study analyses relationships between health status and other variables

OBSERVATIONAL VS EXPERIMENTAL STUDIES

• Experimental or interventional studies: involve an active attempt to change a disease determinant(e.g an exposure or a behaviour) or the progress of a disaese (through treatment)

• The studies are based on a grp which has had the experience compared with control grp which has not had the experience.

PURPOSE OF DESCRIPTIVE EPIDEMIOLOGY

• To generate hypothesis• To permit evaluation of trends in health &

disease and comparisons among countries and subgroups within countries.

• To provide a basis for planning, provision and evaluation of health services

• To identify problems to be studied by analytical methods and to suggest areas that may be fruitful for investigation

CASE STUDIES(CASE SERIES)

• Case reports:documents unusual medical occurrence and can represent the first clues to the formulation of hypothesis, generally report a new or unique findings and previous undescribed disease.

• Case series: collection of individual case reports which may occur within a fairly short time, and experience of a group of patients with similar diagnosis.

Case SeriesAdvantages

Useful for hypothesis generationInformative for very rare disease with few

established risk factorsUsually of short duration.

DisadvantagesCannot study cause and effect relationshipsCannot assess disease frequency

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CROSS-SECTIONAL STUDY• It is also called epidemiologic study or prevalence study

• It analyses (describes)data collected on a group of subjects at one point in time rather than over a period of time. i.e they survey exposure and disease at a single point in time.

• Both exposure and outcome variables are been evaluated at the same point in time(without any inbuilt directionality)

• Most sophisticated descriptive study• It answers the question “WHAT IS HAPPENING RIGHT

NOW?”

QUESTION: “WHAT IS HAPPENING?” NO DIRECTION OF INQUIRY

o onset time end

CROSS-SECTIONAL STUDY

ADV• Best for determining

the status quo(prevalence)

• Quick• Relatively inexpensive

DISADV• Only a snapshot at a

time leading to a misinformation

• Response rate may be low ,with result not representative of the population

Cross-sectional studies

DisadvantagesWeakest observational design,

(it measures prevalence, not incidence of disease). Prevalent cases are survivors

The temporal sequence of exposure and effect may be difficult or impossible to determine

Usually don’t know when disease occurredRare events a problem. Quickly emerging

diseases a problem04/19/23 17

CORRELATIONAL STUDY DESIGN

• A study comparing incidence/prevalence of one event against another on a global scale

• Measures that represent characteristics of entire populations are used to describe the disease in relation to some factor of interest (such as age, calendar time, food consumption, drug use and utilization of health services)

CORRELATIONAL STUDY DESIGN

ADV

• Compares events among nations

DISADV• Doesn’t compare

individuals, so it might lead to overgeneralization.

ANALYTICAL STUDIES

• Two basic designs:• Case – control or retrospective study• Cohort or prospective

• NOTE• There must be a comparison group• No control No conclusion(NCNC)

CASE CONTROL OR CASE HISTORY STUDY

• A group of affected people is compared to unaffected people(the control)

• It’s a LONGITUDNAL STUDY (like cohort study) because it’s a study over a period of time.

• Subjects are selected based on a particular outcome and a study backwards in time to try to detect the causes or risk factors that may have earlier been reported in a descriptive study

• Subjects are then matched and assigned into the two groups. Subject selected on the basis of disease[e.g lung cancer].

• Sometimes called a retrospective study because of the direction of study

CASE CONTROL OR CASE HISTORY STUDY

Advantages of case control

• It is relatively easy to carry out bcos we go back to existing records in the hospital

• It is also rapid and inexpensive• It requires comparatively few subjects• It can assist one in studying different

etiological factors• One does not need an ethical clearance• There is no risk to the subject

Disadvantages of case control

• It introduces bias• To select an appropriate control could be

difficult • It may be difficult to distinguish between the

cause of a disease and an associated factor

COHORT STUDY

• A cohort is a grp of people who have something in common and remain part of a group over an extended time

• A group of people exposed to a suspected etiological agent are compared with a matched control who have not been similarly exposed. Subject selected on the basis of exposure [aetiological factor; cigarette smoking]

• Follow-up over a period to compare the outcome• Also a longitudinal study or prospective study

ADVANTAGES OF COHORT

• There is no bias• The risk can be calculated bcos the incidence

can be calculated• It is effective for studying rare exposures• It allows the study of the natural history of the

disease• It assists in determining the temporal

relationship between the etiological factor & the disease

Disadv of cohort study

• It takes a long time • It is expensive• Large no of subjects are needed• There could be changes in the standard

methods or diagnostic criteria

EXPERIMENTAL STUDIES

• Studies in which 1 grp is deliberately subjected to an experience compared with a control group with no similar experience

• The gold standard in medicine bcos it proves causality

• Can be controlled or uncontrolled

UNCONTROLLED EXPERIMENTAL STUDIES

• Intervention is not compared with a control• The aim is to confirm that the Intervention

made a difference

CONTROLLED EXPERIMENTAL STUDIES

• In this study, a drug or procedure is compared to:

1.Another drug2.Procedure3.Placebo4.Previously accepted tx• The aim is to proove the difference due to tx

CONTROLLED EXPERIMENTAL STUDIES

• Blind trial-single or double• Control could be:A.METHODOLOGY1.Concurrent or parallel: randomized or non-

randomized(quasi)2.Sequential control: self controlled or cross

over3.External control

B. STUDY POPULATION1.Clinical trials2.Field trials3.Community trials

EXPERIMENTAL STUDIES

ADV• Best study type• Greatest proove of causality• Gold standard for other

design• Least bias• Proves best tx or procedure

efficacy

DISADV• Greatest expense • Long duration• Unproven facts adopted by

community can hinder study acceptance

overview

CONCLUSION

“What you cant measure you cant control!”epidemiological study methods are used to study your health and my health and its determinants, as we join hands to ensure a healthier us.

THANK YOU FOR LISTENING.