COHORT STUDY.ppt

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    RESEARCH STUDIES

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    RESERCH STUDIES

    THE EPIDEMILOGICAL STUDIES CLASSIFICATION

    DESCRIPTIVE STUDIES: - Individual Case report

    Case series

    - Population Correlation

    Transverse

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    RESERCH STUDIES

    THE EPIDEMILOGICAL STUDIES CLASSIFICATION

    ANALITIC STUDIES:

    - Observational Case control

    Cohort study

    - Experimental Randomized clinical studies

    Clinical trials

    Therapy equivalence studies

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    RESERCH STUDIES

    COHORT STUDY

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    COHORT STUDY

    Longitudinal studies of incidence

    Offers the best information regarding the causality

    Compares two similar groups (exposed unexposed) from the samepopulation (cohort)

    Direct appreciation of the risk

    Types of cohort studies: - prospective

    - retrospective

    - bidirectional

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    COHORT STUDY

    THE DESIGN OF COHORT STUDY

    Objective: demonstrates the importance of a factor in a diseaseetiology.

    The study begins from a population (cohort) without a disease,

    which is stratified in two similar subgroups (lots): the groupexposed and unexposed to the risk factor

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    COHORT STUDY

    COHORT STUDY DIAGRAM

    populationpersonswithoutdisease

    exposed

    unexposed

    with disease

    without disease

    with disease

    without disease

    study direction

    futurepresent

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    COHORT STUDY

    For the group exposed to the risk factor we have to specify:

    The assumed risk factors and the ways of their measurement

    Subjects eligible criteria ( age, sex)

    Tracking period

    The measurement that needs to be taken in order to prevent asubjects loss from the study

    The defining of the used diagnosis procedures

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    COHORT STUDY

    The dates are placed in a contingency table 2x2

    With

    disease

    Without

    disease

    TOTAL

    Exposed to the

    risk factor a b a+b

    Unexposed to

    the risk factor c d c+d

    TOTAL

    a+c b+d a+b+c+d

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    COHORT STUDY

    DATA ANALYSIS

    Incidence =

    Incidence comparison can be done :

    - as proportion (relative risk)

    - as difference (attributable risk)

    No. of cases with disease in a period of time p

    total number of population

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    COHORT STUDY

    RELATIVE RISK = the ratio between the disease incidence from the personsexposed and unexposed to the risk factor.

    R1 = disease risk in exposed groupR0 = disease risk in unexposed group

    Relative risk shows how many times the disease risk is greater in exposedgroups than the disease risk in unexposed group.

    RR

    0

    1

    dc

    cba

    a

    RR

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    COHORT STUDY

    ATTRIBUTABLE RISK = the difference between the disease risk inexposed and unexposed group.

    RA = R1R0

    Attributable risk shows with how much is greater the risk in theexposed group than in the unexposed group.

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    COHORT STUDY

    INTERPRETATION:

    RR RA

    >1 >0 association risk factor disease

    =1 =0 indifferent factor

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    COHORT STUDY

    STATISTICAL ANALYSIS OF THE COHORT STUDY

    The adequate statistic test is Chi test.

    If the result of the statistical analysis is a p value smaller than0,05 then we get a statistically significant result.

    IC = confidence interval = 95%

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    COHORT STUDY

    ADVANTAGES: Good validity

    Offers the best information regarding the causality and the naturalhistory of the disease

    The most efficient measurement of the risk (RR)

    They are efficient in diseases with higher incidence

    Can observe the mechanism of action of the risk factor

    Can observe the late effects of the disease

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    COHORT STUDY

    DISAVANTAGES:

    Expensive

    Cant be repeated

    Requires a long time to finish and a large number of subjects

    Long-term observation is difficult when the disease has a long

    latency period

    Produce errors, especially selection and confusion errors

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    COHORT STUDY

    Testing the following hipothesys was wanted: oral breathing during thechild's growing period favors the appearance of the maxillary compressionsyndrome. For testing the hipothesys, a study in Tirgu Mures was initiated,in which children from 5 kindergardens were included. The children of bothgroups were between 3 and 4 years old and had similar characteristics

    regarding sex distribution, background, feeding habits, the presence ofdento-maxillary anomalies in parents or siblings, the harmoniousdevelopment of the cephalic end, dimentions , intermaxillary and occlusalrelations. 51 children were exposed to the risk factor studied. They wereoral breathing either due to upper airways' obstruction, septumdeviations/adenoids whose surgical treatment was refused by the parents

    or treatment-refractory rhinitis. The group of children not exposed to therisk factor, didn't present oral breathing at rest, and their upper airways'permeability was normal. The maxillary growth of the children in bothgroups was kept under observation for 4 years, tracking the possiblestarting symptoms of the maxillary compression syndrome.