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epidemiologic study designs

To insert your company logo on this slide

  • From the Insert Menu
  • Select “Picture”
  • Locate your logo file
  • Click OK
  • To resize the logo
  • Click anywhere inside the logo. The boxes that appear outside the logo are known as “resize handles.”
  • Use these to resize the object.
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Epidemiologic study designs

Dr. Sunita Dodani

Assistant Professor

Family Medicine, CHS

THE AGA KHAN

UNIVERSITY

PAKISTAN

learning objectives
Learning Objectives
  • To understand the concepts of different study designs
  • To learn about the advantages and disadvantages of several study designs
performance objectives
Performance Objectives

After this lecture the student will be able

  • To recognize concepts of different study designs
  • To appropriately use a study design in research projects
epidemiologic study designs4
Epidemiologic study designs

The basis for the lecture is the distinction between descriptive epidemiology and analytic epidemiology

Descriptive epidemiology:

seeks to measure the frequency in which diseases occur or collect descriptive data on possible causal factors.

Analytic epidemiology:

attempts to specify in more detail the causes of a particular disease”

epidemiologic study designs5
Epidemiologic study designs

Types of Epidemiologic Observational Studies

based on:

  • type of sampling from population - based on Exposure &/or Disease or neither
  • temporal sequence of observation - one time point, forward, backwards
epidemiologic study designs6
Epidemiologic study designs

Types of Studies

A. Experimental - study factor is manipulated by the investigator

Types

1. Pure versus Quasi-experimental

2. Laboratory versus real world

B. Observational - no manipulation of study factor by the investigator

1. Descriptive versus Analytic

2. Retrospective versus Prospective

epidemiologic study designs7
Epidemiologic study designs

Factors Important in Study Design

A. Specific, testable hypotheses - NOT a fishing expedition

B. Biases

1. Internal validity

2. External validity

epidemiologic study designs8
Epidemiologic study designs

Study designs

Case series

  • Case Series report new diseases or health related problems.
  • They may provide some descriptive data on exposures to potential causal factors
epidemiologic study designs9
Epidemiologic study designs

Cross-sectional studies

  • Cross-Sectional Studies measure existing disease and current exposure levels.
  • They provide some indication of the relationship between the disease and exposure or non-exposure
epidemiologic study designs10
Epidemiologic study designs

Cross Sectional Studies(contd)

  • sample without knowledge of Exposure or Disease
  • sample at one point in time
  • Mostly prevalence studies/surveys
epidemiologic study designs11
Epidemiologic study designs

Cross Sectional Studies(contd)

Advantages

  • Good design for hypothesis generation
  • Can estimate overall and specific disease prevalence and sometimes rates
  • Can estimate exposure proportions in the population
  • Can study multiple exposures or multiple outcomes or diseases
epidemiologic study designs12
Epidemiologic study designs

Cross Sectional Studies(contd)

Advantages

  • Relatively easy, quick and inexpensive
  • No issue of subjecting any animals or producers to particular treatments
  • Best suited to studying permanent factors (breed, sex, blood-type)
  • Often good first step for new study issue
epidemiologic study designs13
Epidemiologic study designs

Cross Sectional Studies

Disadvantages

  • Impractical for rare diseases
  • Not a useful type of study for establishing causal relationships
  • Confounding is difficult to control
  • No control over sample size for each exposure by disease subclass
epidemiologic study designs14
Epidemiologic study designs

Cross Sectional Studies

Disadvantages

  • Problems with temporal sequence of data
  • hard to decide when disease was actually acquired
  • disease may cure the exposure
  • miss diseases still in latent period
  • recall of previous exposure may be faulty
epidemiologic study designs15
Epidemiologic study designs

Case-control studies

  • Case-Control Studies identify existing disease/s and look back in previous years to identify previous exposures to causal factors.
  • Cases are those who have a disease.
  • Controls are those without a disease.
  • Analyses examine if exposure levels are different between the groups.
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Epidemiologic study designs

Case-control studies

Advantages

  • Best design for rare diseases
  • Can be accomplished quickly since events of interest have already occurred
  • Can study several potential exposures at the same time
  • Lends itself well to hospital-based studies and outbreaks
epidemiologic study designs17
Epidemiologic study designs

Case-control studies

Disadvantages

  • Problems with temporal sequence of data
  • Hard to decide when disease was actually acquired
  • Disease may cure the exposure
  • Miss diseases still in latent period
  • Can’t calculate incidence, population relative risk or attributable risk
  • HIGH potential for bias
epidemiologic study designs18
Epidemiologic study designs

Cohort Studies

  • In a cohort study, subjects with an exposure to a causal factor are identified and the incidence of a disease over time is compared with that of controls (persons who do not have the exposure).
  • In a longitudinal study, subjects are followed over time with continuous or repeated monitoring of risk factors or health outcomes, or both.
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Epidemiologic study designs

Cohort Studies

Advantages

  • Can get best assessment of exposure and can deal with changes in exposure
  • May be only design if exposure needs to be measured directly
  • Allows study of rare exposures
  • Only way to get prospective information for rapidly fatal diseases
  • Good for establishing temporal sequence and natural history of disease
  • Can examine multiple outcomes linked to exposure - often find other effects than
epidemiologic study designs20
Epidemiologic study designs

Cohort Studies

Advantages

  • Can estimate overall and specific disease rates, usually incidence
  • Researcher selects, measures & records data
  • Lower potential for bias than a case-control study - no recall and selection bias
  • Results are considered more conclusive than results from case-control studies
  • The longer a cohort study continues, the stronger it can become
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Epidemiologic study designs

Cohort studies

Disadvantages

  • Impractical for rare diseases - even if risk is high, no cases may occur or results
  • may not be statistically significant
  • Larger sample size than case-control
  • Data collection is usually very expensive
  • Long time commitment for follow-up
epidemiologic study designs22
Epidemiologic study designs

Other designs:

Time series- test if incidence of disease changes in a population over time

Hybrid- often what is seen in practice

  • Can be efficient and match necessity
  • Can lead to bias and disaster

Meta-analysis

  • Combining results from a range of published studies
  • Established methodology, not just literature review
epidemiologic study designs23
Epidemiologic study designs

What type of study to chose depends on:

  • what is the research question/ objective
  • Time available for study
  • Resources available for the study
  • Common/rare disease or production problem
  • Type of outcome of interest
  • Quality of data from various sources
  • Often there are multiple approaches which will all work
  • Choosing an established design gives you a huge head start in design, analysis and eliminating biases