Post on 14-Apr-2018
7/27/2019 COHORT STUDY.ppt
1/17
RESEARCH STUDIES
7/27/2019 COHORT STUDY.ppt
2/17
RESERCH STUDIES
THE EPIDEMILOGICAL STUDIES CLASSIFICATION
DESCRIPTIVE STUDIES: - Individual Case report
Case series
- Population Correlation
Transverse
7/27/2019 COHORT STUDY.ppt
3/17
RESERCH STUDIES
THE EPIDEMILOGICAL STUDIES CLASSIFICATION
ANALITIC STUDIES:
- Observational Case control
Cohort study
- Experimental Randomized clinical studies
Clinical trials
Therapy equivalence studies
7/27/2019 COHORT STUDY.ppt
4/17
RESERCH STUDIES
COHORT STUDY
7/27/2019 COHORT STUDY.ppt
5/17
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
7/27/2019 COHORT STUDY.ppt
6/17
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
7/27/2019 COHORT STUDY.ppt
7/17
COHORT STUDY
COHORT STUDY DIAGRAM
populationpersonswithoutdisease
exposed
unexposed
with disease
without disease
with disease
without disease
study direction
futurepresent
7/27/2019 COHORT STUDY.ppt
8/17
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
7/27/2019 COHORT STUDY.ppt
9/17
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
7/27/2019 COHORT STUDY.ppt
10/17
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
7/27/2019 COHORT STUDY.ppt
11/17
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
7/27/2019 COHORT STUDY.ppt
12/17
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.
7/27/2019 COHORT STUDY.ppt
13/17
COHORT STUDY
INTERPRETATION:
RR RA
>1 >0 association risk factor disease
=1 =0 indifferent factor
7/27/2019 COHORT STUDY.ppt
14/17
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%
7/27/2019 COHORT STUDY.ppt
15/17
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
7/27/2019 COHORT STUDY.ppt
16/17
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
7/27/2019 COHORT STUDY.ppt
17/17
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.