pemilihan disain studi observasional
Post on 30-May-2018
227 Views
Preview:
TRANSCRIPT
-
8/14/2019 Pemilihan Disain Studi Observasional
1/44
Research Design:Choosing the Study Design
Kimberly R. BarberDirector of Research
McLaren Regional
Medical Center
-
8/14/2019 Pemilihan Disain Studi Observasional
2/44
Yes No
Yes No Yes No
Exposure Outcome Exposure & OutcomeSimulteneous
Exposure Outcome
Assign Exposure?
Experimental Observational
Random allocation Comparison group
RCT Non-RCT
Analyticstudy
Descripstudy
Direction?
Cohort Case-
Control
Cross-
Section
-
8/14/2019 Pemilihan Disain Studi Observasional
3/44
Design to Employ
Dependent on the hypothesis posed.
Is your intent to observe, associate factors, orshow cause and effect?
Are exposure or outcome factors common or
rare?
Are your resources many or constrained?
-
8/14/2019 Pemilihan Disain Studi Observasional
4/44
Types of Study Designs
Observational Designs
Descriptive Analytic
Cross-sectional, Case-control, Cohort
Experimental Designs
Quasi experimentalNon randomized or non control trial
True experimentalRandomized Controlled Trial
-
8/14/2019 Pemilihan Disain Studi Observasional
5/44
Descriptive Studies
No assignment of exposure or risk factor.
Intent is to observe and record.
Record events or activities. Single event or case = Case Report.
Several events or cases = Case Series.
-
8/14/2019 Pemilihan Disain Studi Observasional
6/44
Cross-Sectional Studies
Measurement of risk and outcome at the
same time.
Outcome
Risk factor
-
8/14/2019 Pemilihan Disain Studi Observasional
7/44
Cross-Sectional Design
The only study capable
of calculating
prevalence. Proportion of the
population with
the outcome at any
point in time.
-
8/14/2019 Pemilihan Disain Studi Observasional
8/44
Cross-Sectional Studies (cont)
Most useful if exposure continues right up to
time that outcome is recognized.
Often conducted as screening and
classification preamble to prospective studies.
-
8/14/2019 Pemilihan Disain Studi Observasional
9/44
Application Exercise:
Cross-Sectional Study
Design a cross-sectional study that examines
the relationship between dietary sodium andhypertension in middle-aged men.
What research question can we answer?
-
8/14/2019 Pemilihan Disain Studi Observasional
10/44
Cross-Sectional Studies
Advantages
Cheap and quick studies.Data is frequently available through current
records or statistics.
Ideal for generating new hypothesis.
-
8/14/2019 Pemilihan Disain Studi Observasional
11/44
Cross-Sectional Studies
Disadvantages
The importance of the relationship between the
cause and the effect cannot be determined. Temporal weakness:
Cannot determine if causeprecededthe effect or
the effect was responsible for the cause.
The rules ofcontributory cause cannot be fulfilled.
-
8/14/2019 Pemilihan Disain Studi Observasional
12/44
Case-Control Studies
(Retrospective)
Case/Control Studies.
Group subjects according to the presence orabsence of the outcome.
Review past histories of the subjects for the
occurrence of suspected risk factors.
?
?
DiseaseRisk
-
8/14/2019 Pemilihan Disain Studi Observasional
13/44
Case / Control Studies (cont)
Case / Control studies have two main
purposes:Descriptive
Describe the risk factorprofile for an outcome.
Analytic Analyze associations between outcome and risk
factors.
-
8/14/2019 Pemilihan Disain Studi Observasional
14/44
Application Exercise:
Case / Control Study
Describe a case/control study on the
relationship between childhood obesity,smoking history, and occurrence of
hypertension in middle-aged men.
What research question can we answer?
-
8/14/2019 Pemilihan Disain Studi Observasional
15/44
Case / Control Studies
Advantages
Are good initial explanatory studies.
Investigators can explore multiple risk factorssimultaneously for one outcome.
Are efficient, relatively cheap, and quick. Data available through
chart review.
-
8/14/2019 Pemilihan Disain Studi Observasional
16/44
Case / Control Studies Advantages
(cont)
Well suited for rare diseases.
Since the study begins with subjects who alreadyhave the outcome, it is easier to accumulate
enough subjects for significant results.
-
8/14/2019 Pemilihan Disain Studi Observasional
17/44
Case / Control Studies
Disadvantages
Data Quality
Data with inadequate detail, questionablereliability, or use a different standard to judge
disease severity.
Recall bias
Subjects who have unpleasant experiences mayrecall past differently than control subjects.
-
8/14/2019 Pemilihan Disain Studi Observasional
18/44
Retrospective Studies
Disadvantages (cont)
Sampling bias
Sample usually not representative of all subjectswho could be included.
Other Capable of studying only one outcome at a time
Cannot calculateprevalence or incidence. Subject to confounding factors.
Cannot prove contributory cause.
-
8/14/2019 Pemilihan Disain Studi Observasional
19/44
Cohort Studies(Prospective)
Subjects identified according to the presence
or absence of the risk factor.
Followed over time until the outcome occurs
or becomes evident.
-
8/14/2019 Pemilihan Disain Studi Observasional
20/44
Cohort Studies (cont) Subjects with and without the suspected risk
factorare followed for the development of the
outcome.
The frequency of the outcome is comparedbetween the two groups.
Disease
?
?
R
i
s
k
-
8/14/2019 Pemilihan Disain Studi Observasional
21/44
Cohort Studies (cont)
Cohort studies have two main purposes:
Descriptive Describe the incidence of outcome over time.
Analytic Analyze associations between risk factors and
outcome.
-
8/14/2019 Pemilihan Disain Studi Observasional
22/44
Historical Cohort Studies
(Non concurrent)
The following all happen in the past:
Assembly of the cohort according to the presenceof absence ofrisk factors.
Baseline measurements
Follow-up and outcomes
Exposure
?
?
Disease
-
8/14/2019 Pemilihan Disain Studi Observasional
23/44
Historical Cohort (cont)
Are not retrospective studies.
Subjects are grouped according to the presenceor absence ofrisk factors (past or present).
Subjects in retrospective studies are grouped
according to the presence or absence of theoutcome.
-
8/14/2019 Pemilihan Disain Studi Observasional
24/44
Cohort Studies
Advantages
More powerful design for defining incidence.
Powerful design forassociating the causewith the effect. Can suggest that the cause precedes the effect.
Data can be collected in a comprehensible and
uniform fashion.Exception: historical cohort with same measurement
weaknesses as the case/control.
-
8/14/2019 Pemilihan Disain Studi Observasional
25/44
Cohort Studies
Advantages (cont)
No recall bias.
Cohort designs can examine many outcomesfor potential risk factors under investigation.
-
8/14/2019 Pemilihan Disain Studi Observasional
26/44
Cohort Studies
Disadvantages
Expensive in time, money, and number of
patients necessary to demonstrate significant
differences between groups.
Less likely than retrospective studies to
uncover new risk factors.
Also subject to confounding.
-
8/14/2019 Pemilihan Disain Studi Observasional
27/44
Cohort Studies
Disadvantages (cont)
Loss of valuable information due to patient
attrition.
Patients may change their behaviors or risk
factors after the initial grouping of subjects
resulting in misclassification and studyerror.
-
8/14/2019 Pemilihan Disain Studi Observasional
28/44
Clinical Trial
Experimental study
Unique features: Intervention in the subjects care for the
purposes of the study.
Randomization of subjects.
Control group comparison.Placebo or treatment
-
8/14/2019 Pemilihan Disain Studi Observasional
29/44
Clinical Trial Design
Randomized
Intervention/
Effect
Outcome
X
X
-
8/14/2019 Pemilihan Disain Studi Observasional
30/44
Clinical Trial (cont)
Randomization
Subjects are randomly assigned to control or experimental
group.
Groups are similar in every way except for the intervention
under study.
Each subject has equal probability of being placed in
either group.
-
8/14/2019 Pemilihan Disain Studi Observasional
31/44
Clinical Trials
Advantages
Subject to the fewest methodological biases
of all study designs.
Most powerful study designed to show
contributory cause.
-
8/14/2019 Pemilihan Disain Studi Observasional
32/44
Clinical Trials
Disadvantages
Is the most expensive study design in terms
of money, time, and number of patients. Issues of patient attrition and compliance may
invalidate the results.
Can be problematic forethical reasons.
Use of placeboHarm outweighing benefits
Zero tolerance for some exposures
-
8/14/2019 Pemilihan Disain Studi Observasional
33/44
-
8/14/2019 Pemilihan Disain Studi Observasional
34/44
Choosing the Specific Design
Study design is highly dependent on the type
of analysis. (3)
Type of analysis is dependent on the
hypothesis posed. (2)
The hypothesis is dependent on the intent of
your research. (1)
-
8/14/2019 Pemilihan Disain Studi Observasional
35/44
1. Research Study Intent
Know the problem.
Determine what you
want to conclude.
Formulate the question.
-
8/14/2019 Pemilihan Disain Studi Observasional
36/44
Examples of Intent
I intend to show that aspirin resistance isassociated with the severity of heart disease. I will compare levels of aspirin resistance among
patients with differing severity of heart disease.
I intend to show that breast feeding isprotective against allergies developing in
infants. I will compare rates of allergies among women
who breast feed and those who do not.
-
8/14/2019 Pemilihan Disain Studi Observasional
37/44
2. Research Hypothesis Know the question you
want answered.
Restate the question into
terms of Hoand H
a.
Think aboutcorresponding analysis.
-
8/14/2019 Pemilihan Disain Studi Observasional
38/44
Examples of Hypotheses
Is aspirin resistance associated with heart
disease? Aspirin resistance increases the risk of heart
attack.
Is breast feeding associated with allergies?
Breast feeding decreases the risk of allergies inbabies.
-
8/14/2019 Pemilihan Disain Studi Observasional
39/44
3. Statistical Plan of Analysis
Correlation?
Comparison?
Association?
Difference?
-
8/14/2019 Pemilihan Disain Studi Observasional
40/44
Examples of Analysis
The level of aspirin resistance is compared
between those with heart attack and those
without. Differences in resistance scores between two
groups (Student T-test)
The rate of infant allergies is comparedamong women who breast feed and those
who do not. Relative risk association (Chi square analysis)
-
8/14/2019 Pemilihan Disain Studi Observasional
41/44
-
8/14/2019 Pemilihan Disain Studi Observasional
42/44
Choose Appropriate Design
Cross-sectional.
Case-control.
Cohort.
Clinical Trial.
-
8/14/2019 Pemilihan Disain Studi Observasional
43/44
Apply the Best Design
Think about the
measures to be used.
Know the analysis
required.
Rethink desired
conclusions.
-
8/14/2019 Pemilihan Disain Studi Observasional
44/44
Summary
Study Design key to determining cause or just
association. Each design has unique strengths &
weaknesses.
The design drives the conclusions.
top related