دکتر خلیلی 1

Lucid the way to “ Research” And Follow an “ Evidence Based Medicine”

Evidence Based Medicine Systematic Review Scientific Method Sampling Study Design Measurement National International Published Unpublished?! We will discuss

 A systematic review is a literature review focused on a single question which tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question.literature review

 Published documents national (i.e. IRANMEDEX ) and international (i.e. MEDLINE ) data banks  Unpublished documents ???

 MEDLARS on Line Medical Literature Analysis and Retrieval System For NLM National Library of Medicine (United States)

 Iran Medical Index an Iranian private company includes 155 national journals

QualitativeQuantitativeBasicApplied ObservationalExperimental DescriptiveAnalytic

Qualitative Quantitative Observational Experimental

 Observational  Experimental (Randomized Control Trial - RCT)  Descriptive  Analytic o Cross-Sectional o Case-Control o Cohort

 Case Report  Case series  Cross sectional  Longitudinal  Normative research  Secondary data analysis (summaries, meta-analysis)  Ecological Who? When? Where?

3 important questions to consider:  Definition of the Population  Definition of Case  Definition of risk factors  Are cases and non-cases from an unbiased sample of the population? Cross-Sectional Study or prevalence study Case / Control Target population Prevalence of Dis. = No. of disease / No. of subjects Prevalence of R.F. = No. of risk factor / No. of subjects

Some uses of Cross-sectional Study Identify and describe a problem Information about socio-demographic characteristics Evaluate utilisation rates of services Monitoring health status of a community by regular repeated surveys Collect information for planning e.g. surveys of immunisation or prenatal care coverage

Trend Design in Cross-Sectional studies Population Disease Prevalence Risk Factor Present Sampling Future Risk Factor Disease Prevalence Sampling

In cross-sectional studies Advantages Useful for descriptive studies Rapid, inexpensive, can provide analytic clues. Less prone to error about exposure recall bias Disadvantages Prone to sample distortion bias. Unable to sort out what came first exposure or outcome Prone to seasonal and time to time variations

Case-control Study Population at risk Cases Controls Yes No Yes No people who get the disease people who do not get the disease Compare past "exposures“

In case control studies Case-selection usually clinic- or hospital- based. Controls may also be clinic- or hospital- based, or population-sampled.

First Step Selection of cases  Precise definition of ‘case’.  Inclusion / Exclusion criteria.  How are cases to be identified? How recruited?

Second Step Selection of Controls  Source ( hospital patients without disease; neighborhood controls; random sample of population; sibs).  Inclusion / exclusion criteria. Controls must be related to the same population as the cases are.

Third Step Collection of information  Identify risk factor of interest  Method of collection of information ( questionnaire; medical records; employment records)  Same procedure to be used for cases and controls  Interviewer should be unaware who is a case and who a control.

Results of a Case-Control Study Risk factor Disease Yes (cases)No (controls) Yesac Nobd TotalN1N2 N1 and N2 are fixed numbers

Some Points Two Methods of Selection Select new cases (i.e. incident) as they come up. Controls are selected from those in the same setting at the same time. Select existing cases (prevalent) from a defined population. From the same population a larger number of controls are identified. The Incident type of case-control study is stronger because diagnosis of cases and ascertainment of exposure is being done by the researcher.

Some Points Matched Case-Control Studies cases Non-cases cases Non-cases Cases Controls Matched controls cases Non-cases

Advantages and Disadvantages of Case-control Studies Relatively cheap compared to cohort studies Relatively quick Useful for study of rare diseases. No ethical problems Useful for diseases with long latent period. Estimate of disease incidence cannot be done At times difficult to measure exposure accurately Open to selection bias. Difficult to interpret. AdvantagesDisadvantages