descriptive and cross sectional studies
TRANSCRIPT
-
8/10/2019 Descriptive and Cross Sectional Studies
1/40
Epidemiological study designs
1
-
8/10/2019 Descriptive and Cross Sectional Studies
2/40
The life cycle of epidemiological investigations:
The never ending story
Identifying
data needs
Spelling out the
research question
Formulating the
study objectives
Planning the
analysis
Preparing data
collection instruments
Analysing data
Drawing conclusions
Formulating
recommendations
Involving the
programme
Collecting data
Here we
go again
-
8/10/2019 Descriptive and Cross Sectional Studies
3/40
Descriptive Studies
-
8/10/2019 Descriptive and Cross Sectional Studies
4/40
Epidemiologic Study Designs
Grimes & Schulz, 2002 (www)4Descriptive studies
http://dx.doi.org/10.1016/S0140-6736(02)07283-5http://dx.doi.org/10.1016/S0140-6736(02)07283-5 -
8/10/2019 Descriptive and Cross Sectional Studies
5/40
Epidemiologic Study Designs
Grimes & Schulz, 2002 (www)5Descriptive studies
Descriptive
study
http://dx.doi.org/10.1016/S0140-6736(02)07283-5http://dx.doi.org/10.1016/S0140-6736(02)07283-5 -
8/10/2019 Descriptive and Cross Sectional Studies
6/40
Hierarchy of Epidemiologic Study Designs
Tower & Spector, 2007 (www)
http://taylorandfrancis.metapress.com/content/n708745v34251883/http://taylorandfrancis.metapress.com/content/n708745v34251883/ -
8/10/2019 Descriptive and Cross Sectional Studies
7/40
Descriptive studies 7
Start ofHIV/AIDSResearch
New outbreak of
oral tumors,
malignancies and
infectious diseases
strikes young male
homosexuals
CDAJ, 1982Squamous cell
carcinoma in sexualpartner of Kaposi
sarcoma patient
Lancet,1982
AIDS in the "gay"
areas of SanFrancisco
Lancet, 1983
-
8/10/2019 Descriptive and Cross Sectional Studies
8/40
Meticulous observations by
Burkitt
Epstein Barr Virus
BurkittsLymphomaDescriptive studies 8
-
8/10/2019 Descriptive and Cross Sectional Studies
9/40
Descriptive study - Definition
A study concerned with and
designed only to describetheexisting distribution ofvariables without regard to
causal or other hypotheses(John M. Last).
9Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
10/40
escriptive Studies
Are often the first step inepidemiological investigation
Allow natureto take its course
The simplestof epidemiologicalstudies
Often stimulate the initiationfor moredetailed studies
Descriptive studies 10
-
8/10/2019 Descriptive and Cross Sectional Studies
11/40
Descriptive Study VsAnalytical Study
Descriptive Study Analytical Study
Concerned with characteristicsthe amount and distributionof disease within a population
Concerned with determinants ofdisease, reasons for relatively
high or low frequency ofdisease in specific population
subgroups
Used to identify any healthproblem that may exist
Proceed to identify the causesof the problem
Generateshypothesis Testshypothesis
Precedesanalytical study Followsdescriptive study
11Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
12/40
Prevalence of smoking in adultmen in South India
Country
Percentage of smokers
Urban Rural
Tamilnadu 66 88
Kerala 88 84
Karnataka 76 41
Andhrapradesh 57 75
Descriptive studies 12
-
8/10/2019 Descriptive and Cross Sectional Studies
13/40
Prevalence of Flourosis, India
Descriptive studies 13
-
8/10/2019 Descriptive and Cross Sectional Studies
14/40
Procedures in Descriptive studies
1. Defining the populationto bestudied
2. Defining the diseaseunder study
3. Describing the diseaseby person,place & time
4. Measurementof disease
5. Comparingwith known indices6. Formulation of an etiological
hypothesis
15Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
15/40
1 Defining the population to be studied
Investigations of populations notindividuals
Total number, age, sex, occupation, etc.,
Whole population or a representativesample or a selected group
The chosen community should be stable
A close health facility
Defined population is the Denominator
16Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
16/40
2. Defining the disease under study More investigators / interviewers may be involved
Epidemiologist Operational definition
Precise Clearly indicates who is a case
Valid The identified case should actually have the disease
Acceptable to the population Too many decline consent Applicable to large numbers
Eg. Malaria
Epidemiologist frames his own definition if necessary
Adherence
17Descriptive studies
3 D ibi h di b
-
8/10/2019 Descriptive and Cross Sectional Studies
17/40
3. Describing the disease byperson, place & time
Person Place Time
Age, Sex, Height,Weight
Country, Region Year, Season
Birth order, Familysize
Urban, Rural, Localcommunity
Month, Week
Occupation,
Education, socialstatus
Towns, Cities Day, Hour of onset
Blood pressure,Blood cholesterol
Institutions Duration
18Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
18/40
4. Measurement of disease
Mandatory to know the Burden ofillness.
Morbidity, mortality, disability etc.,
Mortality straightforward
Morbidity two aspects
Incidence from longitudinal studies
Prevalencefrom cross sectionalstudies
19Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
19/40
5. Comparing with known indices
Essence of epidemiology
Between different populations,
subgroups of same population
Provides clues to etiology
Also identifies groups which are atincreased risk for certain diseases
20Descriptive studies
l f
-
8/10/2019 Descriptive and Cross Sectional Studies
20/40
6. Formulation of anetiological hypothesis
Hypothesis- supposition arrived at fromobservation or reflection that can be tested bycollecting facts that lead to their acceptance
or rejection. It is a refutable prediction. Hypothesis should be complete and specific
a. Population
b. Specific cause considered
c. Expected outcome
d. Dose response relationship
e. Time response relationship
21Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
21/40
For Example:
Cigarette smoking causes lung
cancer
Descriptive studies 22
-
8/10/2019 Descriptive and Cross Sectional Studies
22/40
Smokingof30 40cigarettes per daycauses
lung cancer in 10% ofsmokers after20 years of
exposure
Descriptive studies 23
-
8/10/2019 Descriptive and Cross Sectional Studies
23/40
Smokingof30 40cigarettes per daycauses
lung cancer in 10% ofsmokers after20 years of
exposure
Descriptive studies 24
POPULATION
-
8/10/2019 Descriptive and Cross Sectional Studies
24/40
Smokingof30 40cigarettes per daycauses
lung cancer in 10% ofsmokers after20 years of
exposure
Descriptive studies 25
SPECIFIC
CAUSE
POPULATION
-
8/10/2019 Descriptive and Cross Sectional Studies
25/40
Smokingof30 40cigarettes per daycauses
lung cancer in 10% ofsmokers after20 years of
exposure
Descriptive studies 26
OUTCOME
SPECIFIC
CAUSE
POPULATION
-
8/10/2019 Descriptive and Cross Sectional Studies
26/40
Smokingof30 40cigarettes per daycauses
lung cancer in 10% ofsmokers after20 years of
exposure
Descriptive studies 27
OUTCOME
DOSESPECIFIC
CAUSE
POPULATION
-
8/10/2019 Descriptive and Cross Sectional Studies
27/40
Smokingof30 40cigarettes per daycauses
lung cancer in 10% ofsmokers after20 years of
exposure
Descriptive studies 28
OUTCOME
DOSESPECIFIC
CAUSE
POPULATION
TIME-RESPONSE
RELATIONSHIP
f
-
8/10/2019 Descriptive and Cross Sectional Studies
28/40
Types of Descriptive Studies
Case Report & Case Series
Descriptive Cross-sectional
Studies (Community Surveys)
Ecological Descriptive Studies
29Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
29/40
Case Report & Case Series
A case study (case report) is a methodof descriptive research thatdocuments a practitioners
experiences, thoughts, orobservations related to the care of a
singleclient of a specific condition.
A case series combines theobservations from a group of similarclients
30Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
30/40
Benefits of case studies
Convey detailed information that mightbe lost in a clinical trial throughdocumentation of actual events andinterventions in clinical practice
Are faster and less expensive tocomplete than clinical trials
Provide a rationale for furtherinvestigation
31Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
31/40
Descriptive Cross-sectional Studies(Community Surveys)
Simplest of descriptive studies
Based on a single examination of across-section of population at one point
of time. Also known as Prevalence survey.
A survey with questions used to describea population
Do you take vitamins?
What vitamins do you take?
When do you take them?32Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
32/40
Ecological Descriptive Studies
When the unit of observation is anaggregate (e.g. family or school) of anecological unit (a village, town or
country) the study becomes anecological descriptive study.
Eg:Esophageal cancer rates in Japan
Eg: Occurrence of higher number ofrespiratory illness in different citieswith different levels of pollution.
33Descriptive studies
-
8/10/2019 Descriptive and Cross Sectional Studies
33/40
Uses of Descriptive studies
Provide data regarding the magnitude ofthe disease load and types of diseaseproblem in the community in terms ofmorbidity and mortality rates
Provide clues to etiology Provide background data for planning,
organizing and evaluating preventive andcurative services
Contribute to research by describingvariations in disease occurrence byPerson, Place & Time
Descriptive studies 34
-
8/10/2019 Descriptive and Cross Sectional Studies
34/40
Cross-Sectional Studies
Begin with Cross-sectional sample
Determine Exposureand Diseaseat same
time
-
8/10/2019 Descriptive and Cross Sectional Studies
35/40
Cross-sectional study
-
8/10/2019 Descriptive and Cross Sectional Studies
36/40
Cross-sectional studies
-
8/10/2019 Descriptive and Cross Sectional Studies
37/40
Cross-sectional No direction
Exposure
(Risk Factor)
Disease(Outcome)+
+
_
_
-
8/10/2019 Descriptive and Cross Sectional Studies
38/40
Ill Non-ill Total
Exposed a b a+b
Non-exposed c d c+d
Total a+c b+d a+b+c+d
Presentation of the data of a cross-sectional
study in a 2 x 2 table
Known simultaneously when the study is completed
-
8/10/2019 Descriptive and Cross Sectional Studies
39/40
Risk measurement from a
cross-sectional study
Prevalence of illness among exposed and
compare it with that of non-exposed
a/a+b /c/c+d Prevalence of exposure among ill and
compare it with that of non-ill
a/a+c /b/b+d
-
8/10/2019 Descriptive and Cross Sectional Studies
40/40
Thank you!
D i i di 41