Study Methods

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• Aim of epidemiological studies

• To determine distribution of disease
• (Descriptive Studies)
• To examine determinants of a disease
• To judge whether a given exposure causes or
  prevents disease
• (Analytical Studies)

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Research Methods

• Qualitative
• Quantitative

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Study Design

• Major study designs differ based on
• Number of observations made
• Directionality of exposure
• Data collection methods
• Timing of data collection
• Unit of observation
• Availability of subjects

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• Which Design Is Best?

• Which Design Is Best?

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• It depends on .

• Regulations
• Time urgency
• How much is known about the association
• Money
• Whether the exposure is believed to be
  beneficial

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Case Reports / Case Series

• Case reports describe the experience of a single
  patient or group of patients with a similar DX.

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• Case Reports / Case Series

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• Case Report example

• In 1961, a published case report of a 40
  year-old woman who developed pulmonary embolism
  after beginning use oral contraceptive

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Important Case Reports

• These all started with case reports - what study
  design next?
• Lyme Disease (1975)
• Legionellosis (1976)
• AIDS (1981)
• Hantavirus (1993)
• DES exposure (1989)
• EMS l-tryptophan (1970)
• TSS (1980)

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• Case Series example

• In Los Angeles, five young homosexuals men,
  previously healthy, were diagnosed with
  pneumocyst cariini pneumonia in a 6-month period
  (80-81)

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• Cross Sectional Studies

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• Cross Sectional Studies

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• Yes

• No

• Total

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• a

• Yes

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• a b

• No

• d

• c

• c d

• b d

• a c

• N

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• Cross Sectional Studies

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  ????

• Yes

• No

• Total

• 90

• 87

• 3

• Yes

• ???? ????

• No

• 75

• 89

• 14

• 162

• 17

• 179

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Prevalence Studies

• Incident cases
• All new cases arising in a defined population

• Time

• Prevalent Cases
• Present at a point in time

• Leave Population
• Severe disease, Mild disease, Move

• Early Deaths

• Cures

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Case control studies

• epidemiologists use them to study a huge variety
  of associations.
• more frequently than other analytical studies

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Case-control study

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• ? --------------------------------------------

• ?????? ?????? (-)
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• Investigator

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Retrospective vs. prospective

• Retrospective
• (Case-control)

• Disease

• Present
• (Cases)

• Absent
• (Controls)

• Risk Factor

• Present
• (Exposed)

• b

• a

• Prospective
• (Cohort)

• Absent
• (Not Exposed)

• d

• c

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Example of an experiment

• Population 1

• Population 2

• Ascorbic Acid

• Placebo

• Outcomes

• Do the average number of colds differ?

• Do their average lengths of colds differ?

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• TYPES OF STUDIES

• Experimental(Interventional)
• observational

• Primary
• secondary
• (review article)

• Narrrative
• systematic

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Systematic Review

• A systematic review is an overview of primary
  studie
• A meta-analysis is a mathematical synthesis of
  results of two or more primary studies
• Although meta-analysis can increase the
  precision of a result, it is important to
  ensure that the methods used for the review were
  valid and reliable

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• The Evidence Pyramid

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• Intuition and Logic in Research

• Dominant Mental Activity

• Intuition
• Feeling
• Judgement
• Experience

• Analysis
• Experiment

• Clinical trials

• Hi

• Cohort Study

• Case-control Study

• Cross-sectional Study

• Control over variance

• Case Report
• Case Series

• Qualitative
• Research

• Lo

• Potential for Misinterpretation

• Lo

• Hi

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