Paper II: Clinical Epidemiology Part A research designs An overview Unit2 : Research designs

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Paper II Clinical EpidemiologyPart A- research
designs- An overviewUnit-2 Research designs
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Contents

• Refining a research question, steps Asking ,
  refining
• Purpose of research
• Types of designs
• Programme evaluation
• Protocol preparation
• Hypothesis
• Process of data collection

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Epidemiology

• Study of the distribution determinants of
  health related states and events in a specified
  population and the application of this for the
  prevention and control of health problem
• John. M.Last

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Research design

• Framework in which investigation is planned and
  carried out
• Based on the type of research question
• Guides subject selection, methods of
  investigation and the statistical principles
• An appropriate research design is a prerequisite
  for a valid study

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Study designs

• Observational
• Descriptive Studies
• Case studies and Case series
• Surveys
• Cross Sectional
• Longitudinal
• Qualitative
• Analytical Studies
• Ecological
• cross sectional
• Case control
• Cohort
• Experimental

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Case Series

• Australian gynaecologist, Dr. McBride
  of Sydney, suspected that thalidomide was the
  cause of limb and bowel malformations in three
  children he had seen at Crown Street Women's
  Hospital. 1956

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• Pneumocystis carinii pneumonia and mucosal
  candidiasis in previously healthy homosexual men
  evidence of a new acquired cellular
  immunodeficiency1981 Dec 10305(24)1425-31.
• MS Gottlieb, R Schroff, HM Schanker, JD Weisman,
  PT Fan, RA Wolf, and A Saxon

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Case Reports/ Case Series

• The most basic descriptive study.
• Link between clinical medicine and epidemiology
• Hypothesis generating.
• Rarely the evidence can even be strong!!

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Surveys

• Pre planned
• Single group studies
• Conducted on population or samples from
  population
• Used to describe in quantitative terms the
  disease burden
• Prevalence and incidence are obtained from
  surveys
• The denominator i.e. the population at risk -
  clearly defined
• Generates hypothesis with regard to cause and
  effect
• Does not prove the association.

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What is Qualitative research

• Qualitative Research documents the world from the
  point of view of the people studied-Hammerseley,19
  92
• To understand people and peoples behaviour we
  have to understand the meaning and interpretation
  that people give to their behaviour
• Phenomenological
• It is concerned with meaning, interpretation and
  processes

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Case Control Studies
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Case Control Studies
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• Advantages
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•   Easier, cheaper and more feasible
•   Useful to study rare diseases
•   Most useful for diseases with prolonged
  exposure time
•   Can look at multiple risk factors

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• Limitations
• Choice of controls sometimes difficult Eg.
  Cancer, CAD
• Polygenic diseases - Cluster effect difficult
  to choose appropriate controls
• Cannot compute risk of disease
• Temporality questionable

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Cohort Studies
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Cohort Studies
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Cohort Studies
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• Advantages
• Temporality as in real life
• Useful for diseases with high prevalence
• When one exposure gives risk to multiple diseases
• When exposure is rare
• Measures absolute and relative risk of disease.

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• Limitations
• Slow, time consuming, costly.
• Not useful in diseases with long latency
• Difficult to assess independent effect of
  multiple risk
• factors.
• Eg. Framingham study
• .

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 Ecological studies

• Measures combined occurrence of risk factors and
  disease in a population
• Individual exposure and disease relationship
  cannot be assessed
• Eg Occupational and industrial exposure to
  toxins, Environmental risk
• Average risk Ecological fallacy

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Ecological Studies
Narendranathan, Alapuzha 2002
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Association or causation?
Ear lobe crease means increased heart disease
Will surgical excision help?
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Bradford Hills Criteria of Causation

• Experimental evidence
• Strength of association
• Consistency
• Temporal relationship
• Biologic gradient
• Biologic plausibility
• Coherence
• Specificity
• Analogy

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Experimental designs

• Clinical trials
• Field trials
• Community trials

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Experimental designs

• RCT
• Non RCT- Quasi experimental
• Historical control
• Natural experiment
• Nonequivalent comparison group
• Time series
• Before and after intervention without control
• Before and after intervention with control

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Experimental Designs

• A. Post-only design
• B. Pre and post design
• C. Multiple Levels of single IV
• D. Multiple Experimental and Control Groups
• E. Multiple IVs (Factorial design)

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Experimental Designs

• Concurrent parallel designs
• Cross- over designs

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Experimental Designs

• RCT
• Preventive trials
• Clinical trial
• Risk factor trials
• Cessation experiments
• Trial of aetiological agent
• Evaluation of health services

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Randomized Controlled Trials
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Randomized controlled trial of early hospital
discharge after myocardial infarction
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Field trial of vaccine against NEW World
cutaneous leishmaniasis(NWCL)
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 Advantages and Limitations

• Advantage - Best evidence
• Limitations
• Randomisation not possible in all settings
• Blinding to avoid bias
• Ethics
• Feasibility
• Cost
• Appropriate sample sizes are a prerequisite or
  else one may end up with false negative
  conclusions

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STUDY QUESTIONS AND APPROPRIATE DESIGNS Type of
Question Appropriate Study Design Burden of
illness - Prevalence Cross Sectional
Survey - Incidence
Longitudinal survey Causation, Risk Prognosis
Case Control Study, Cohort
study Occupational risk, Environmental Risk
Ecological studies Treatment Efficacy
Randomized Controlled study Diagnostic Test
Evaluation Randomized Controlled study Cost
Effectiveness Randomized Controlled study
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Meta-Analysis
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Meta-Analysis
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Evidence Pyramid
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Misconception!

• For every research project there is one single
  best design to answer the question
• It is the design which decides the value of a
  study

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Evaluation

• Evaluation is the critical assessment on an
  objective basis as possible, of the degree to
  which entire services or their component parts
  fulfill stated goals
• Evaluation is the process of making judgement
  about selected objectives and events by comparing
  them with specified value standards for the
  purpose of deciding alternate course of action

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Evaluation vs Pure research

• Systematic investigation of the evaluated and
  aims to discover new knowledge
• Methods are chosen and combined in a process
  called evaluation
• Has a practical focus aimed at making informed
  decisions

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Perspectives of evaluation
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Types of evaluation

• Before an intervention - evaluability assessment,
  Need, feasibility assessment, predictive,
  simultaneous, front end
• During the intervention process , formative and
  pluralist
• After the intervention - Outcome, Impact and
  summative

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Process Evaluation

• Purpose
• Accountability
• Programme development Improvement
• To help others set up similar services
• Is the programme accomplishing what it is
  expected to achieve
• Focus is on process
• Understanding of how a service operates and how
  the service provides what it is supposed to, or
  to know why a service is effective
• Experimental methods not used
• Preferred designs Qualitative -case study and
  descriptive designs
• Methods In depth interviews , Focus group
  discussion, documentary analysis

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Hypothesis
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Hypothesis

• H0 may usually be considered the skeptics
  hypothesis Nothing new or interesting happening
  here! (And anything interesting observed is
  due to chance alone.)
• Ha may usually be considered the researchers
  hypothesis.

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Hypothesis

• The null hypothesis, denoted H0, is the claim
  that is initially assumed to be true. The
  alternative hypothesis, denoted by Ha, is the
  assertion that is contrary to H0
• Possible conclusions from hypothesis-testing
  analysis are reject H0 or fail to reject H0.

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Rules

• H0 is always stated as an equality claim
  involving parameters.
• Ha is an inequality claim that contradicts H0.
  It may be one-sided (using either gt or lt) or
  two-sided (using ?).

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Test of hypotheses

• A test of hypotheses is a method for using sample
  data to decide whether the null hypothesis should
  be rejected.

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Errors in Hypothesis Testing
A type I error consists of rejecting the null
hypothesis H0 when it was true. A type II error
consists of not rejecting H0 when H0 is false.
are the probabilities of type I and type II
error, respectively.
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Protocol Prepration
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What is a protocol

• Protocol is BLUEPRINT for action
• It is a STATEMENT of intention
• It is an ACTION PLAN for future reference
• It is a ROADMAP that helps you reach where you
  want to reach
• It is a COMMUNICATION TOOL to tell others of what
  you want to do

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Contents of a protocol

• Introduction
• Background and rationale Why?
• Objective or research question
  Explicit/Implicit- What?
• Methodology
• Study design
• Setting Where?
• Subjects - Inclusion and exclusion criteria- Who?
• Sample size and sampling technique How many?
• Study period- When?
• Implementation/Data collection How?

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Contents of a protocol

• Implementation/Data collection How?
• Tools- Questionnaire, validated instruments,
  scales
• Definition of study variables
• Resources
• Manpower
• Money Budget (for funding)
• Materials
• Manhours Time line chart /GNATT chart
• Technique/Procedure

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Contents of a protocol

• Analysis Plans, dummy tables
• Ethical considerations
• IEC clearence
• Consent from authorities
• Informed written consent of subjects
• references

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Thank you for listening