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Study Design
Dr Syeed Mehbub Kadir
Fellow of Orbit & Ophthalmic Plastic Surgery
Sankar Institute of Ophthalmology
Visakhapatnam
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Objectives
To understand the difference between descriptive and analytic studies
To identify the hierarchy of study designs, and the strengths and weakness of each design
To be able to apply different study designs to the same research question
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Study Design
Experimental• Randomized controlled trials• Quasi
Observational
Analytic • Cross sectional• Case-control• Cohort studies
Descriptive• Case report• Case series• Survey
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Grimes & Schulz, 2002 (www)
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Observational/ Non-interventional study
Descriptive study:
- Case report
- Case series
- Population study (survey) Analytical study:
- Cross-sectional
- Case-control
- Cohort
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Descriptive studies
Case report
Primary mucinous carcinoma of eyelid: A rare clinical entity
Hemi-CRAO in Young Adult
case series
Eyelid malignancies: A clinico-pathologic studies
A Study on Pattern and Nature of Age Related Macular Degeneration (ARMD) patients attending in SFEH
Surveys How many patients did macular hole surgery at SFEH in 2010?
A prevalence survey of Trachoma in hilly area of visakhapatnam
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Descriptive Studies: Uses
Hypothesis generating
Suggesting associations
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Analytical Studies
Cross-sectional study
Case control study
Cohort study
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Cross-sectional Study
Data collected at a single point in time
Describes associations
Prevalence
A “Snapshot”
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* 1000
Prevalence:Point prevalence-Number of all current cases (new & old) at a point in time
Population at the same point in time
Period prevalence
Number of all current cases (new & old) over a period of time
Mid year population at risk
Incidence rateThe no of new cases of a specific disease in a given time
Population at risk during that time
Prevalence vs. Incidence
* 100
* 100
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Cross-sectional Study
Sample of Population
Smokers Non-smokers
Prevalence of TAO Prevalence of TAO
Time Frame = Present
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Example of a Cross-Sectional Study
1. Association between Smoking and TAO patients
attending in the Orbit & Ophthalmic Plastic services
2. To assess the rate of CNVM among ARMD patients
attending in the Dept of Vitreo-retinal services
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Cross-sectional Study
SMOKING
-
T
A
O
+
- 90
10 90
10
+
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Cross-Sectional Study
Strengths
Prevalence (not incidence)
Fast/Inexpensive - no waiting!
No loss to follow up
Associations can be studied
Weaknesses
Cannot establish cause-effect
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Prospective study:
Forward looking study (Present ⇨ Future)
Risk factors/ Cause outcome of disease
e.g- Cohort study
Retrospective study: Backward looking study (Past ⇦ Present)
Disease Risk factors/ Cause
e.g.- Case-control study
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Case-Control Study
Start with people who have a disease
Match them with controls ēout disease
Look back and assess exposures
Retrospective study
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Case-Control Study
Patients with CRVO
Patients w/o CRVO
Present (Outcome)
Past (Exposure)
Hypertensive
Hypertensive
Non hypertensive
Non hypertensive
Cases
ControlsComparison
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Example of a Case-Control Study
An evaluation of Optical Coherence Tomography
(OCT) measurement of macular and retinal nerve
fibre layer thickness of normal and glaucomatous
eye
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Case-Control Study
Patients w POAG
Patients w/o PAOG
Present (Outcome)
Past (Exposure)
RNFL thickness by OCT
RNFL thickness by OCT
Cases
Controls
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Case-Control Studies: Strengths
Good for rare outcomes: cancer
Can examine many exposures
Useful to generate hypothesis
Fast & cheap
Smaller Sample is required
Provides Odds Ratio
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Case-Control Studies: Weaknesses
Cannot measure
Incidence
Prevalence
Relative Risk
Can only study one outcome
High susceptibility to bias
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Measures of association
Disease
Yes No
Risk factors
Yes A B
No C D
Sensitivity = A/A+C
Specificity = D/B+D
Odds ratio: AD/BC
1= no diff. case & control>1 = risk more
< 1 = risk less
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Cohort Study
Begin with disease-free patients
Classify patients as exposed/unexposed
Record outcomes in both groups
Compare outcomes using relative risk
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Prospective Cohort Study
Exposed to risk factors
Not exposed to risk factors
Do not develop disease
Develop disease
Develop disease
Do not develop disease
Present Future
comparison
Study population wo disease
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Example of a Cohort Study
1. To see the effects of smoking on TAO in a population
2. To assess the of radiation on Lung cancer staffs of
radiotherapy dept
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Cohort study: Tobacco smoking and lung cancer, England & Wales, 1951
Cigarettes smoked/d
Person-years at risk
Cases Rate per 1000 p-y
Rate ratio
≥ 25
15 – 24
1-14
none
25,100
38,900
38,600
42,800
57
54
22
03
2.27
1.39
0.57
0.07
32.4
19.8
8.1
Ref.
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Measures of Association
Disease Yes No
Yes A BRisk Factor NO C D
Risk ratio (relative risk) __ ___A___ _ A + B____ ___ _C_____ C + D
RR = 4 means 4 times risk in exposure than normal
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Cohort Study: Strengths
Can calculate incidence data & relative risk
Less bias than case control study
Retrospective may be done
Can measure multiple outcomes
Can adjust for confounding variables
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Cohort Study: Weaknesses
Expensive
Time consuming (long term study)
Cannot study rare outcomes
Confounding variables
Exposure may change over time
Disease may have a long pre-clinical phase
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What distinguishes observational studies from experiments?
Ability to control for confounding
Predictor Outcome
Confounder
Examples: Smoking
Male Dysthyroid optic neuropathy
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Clinical Trials
Criteria
Randomized
Blinding
Controlled
This scientific study
provides us ē the
information of the efficacy
& usefullness of a new
drugs, vaccine, surgical
procedures, innovations &
interventions etc.
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What is Blinding?
Single blind - participants are not aware of Rx group
Double blind - both participants and investigators
unaware
Triple blind - various meanings
persons who perform tests
outcome adjudicators
safety monitoring group
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Clinical Trial
Study Population
Treatment Group
Control Group
Outcomes
Outcomes
R a n d om i z e
Comparison
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Clinical Trial
Patients w Ocular lymphoma
Randomi ze
Ivt Rutiximab
Ivt methotrexate
Comparison
Outcome
Outcome
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Phases of RCT (Drugs)
Phase I: Healthy volunteers (limited no.)
Phase II: On Patients (limited no.)
Phase III: Large no of patients in multicentre evaluation
Phase IV: Post marketing survillence
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Clinical Trials
Strengths: Best measure of causal relationship
Best design for controlling bias
Can measure multiple outcomes
Weaknesses: High cost
Ethical issues may be a problem
Compliance
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Quasi study
The interventional study does not fulfill the following
criteria:
- Randomization
- Controlled
- Blinding
## Chance of Biasness is more
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Analytical Studies:Summary
Cross-Sectional
Case-Control
Cohort RCT
Cost + ++ +++ ++++
Duration + ++ +++ +++
Sample Size
Varies Small Large Varies
Incidence, Prevalence
Prevalence None Incidence Incidence
Multiple Outcomes
Yes No Yes Yes
Bias Prone Yes Yes No No
Causality No No No Yes
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Quiz- Study design?
1. A Study of Visual Improvement Following Occlusion Therapy as Treatment of Amblyopia in the Older Child.
2. Role of acyclovir on Herpetic epithelial keratitis-Comparison among oral, topical and both routs of administration.
3. Lateral Tarsal strip technique for correction of lower eyelid Ectropion.
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Quiz
4. Evaluation of surgical outcome of LPS resection
5. Comparison of corneal endothelial cell loss during
phacoemulsification using continuous anterior chamber
infusion versus those using ophthalmic viscosurgical
device
6. A study of the consequence of cataract patients living
in the rural area
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Quiz- Study design?
7. Relation between retinal vein occlusions and
axial length – A comparative study
8. A study of LASER DCR with or without silicone
tube intubation
9. Evaluation of single stage adjustable strabismus
surgery under conscious sedation
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How to write a abstract
Abstract is a miniature version of the scientific paper. It
should provide a brief summary of each of the main
sections of the paper such as Title Author/ Authors name Purpose/ Aim Results Conclusion
Keywords: Authors must provide 4-6 keywords
< 250 words in length & constructed as a single paragraph
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Guidelines for abstract
Abstract should be written in the past tense
It should not contain abbreviations/acronyms
It should not contain anything that is not in the paper
It should not contain any ref, figure or table
It should not contain the place of study
Language should be simple & clear
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Lateral Tarsal strip technique for correction of lower eyelid EctropionMohamed A. Marzouk* , Ayman A. Shouman , Ehab S.Elzakzouk and M.Tarek A.Elnaggar
Abstract: Purpose: To evaluate lateral tarsal strip technique as a simple procedure that can be used in the presenceof lateral canthal tendon laxity or malposition. The technique was used in this study on cases of involutional ,paralytic, and cicatricial ectropion .The surgical outcome from different types of ectropion was compared andevaluated. Patients and methods: This retrospective study reviewed records of 30 patients (41 lids) who had undergone lateral tarsal strip from January-2008 to June-2010. All records were examined to determine the indications, management, outcome, postoperative complications and success rate. Results: A total of 17 males and 13 females made up the study groups. The mean age of the cohort was 59.15 +\- 6.2 yrs(range 4- 65 years).The average follow up period was 24 weeks .The patients were divided into 3 groups:Group A: 10 patients with bilateral involutional ectropion (20 lids). Group B: 10 patients with unilateral paralytic ectropion (10 lids). Group C: 10 patients with cicatricial ectropion 9 unilateral and 1 bilateral (11 lids). Most common presenting feature was persistent tearing, which was seen in all patients, others included lid laxity, lagophthalmos and unacceptable cosmesis. Thirty-five lids obtained satisfactory correction of eyelid ectropion with a simple lateral tarsal strip surgical procedure, while six lids required additional intra operative ancillary procedures to correct the remaining skin laxity, scleral show and residual ectropion. Common ancillary procedures used were excision of skin and muscle strip, lateral tarsorraphy and scar revision in severe cicatricial ectropion. Good aesthetic and functional results were achieved in 85% of cases. Conclusions: Lateral tarsal strip is a simple technique, which can be used in different types of eye lid ectropion. The technique is directed at correcting the anatomical defect, preserving the natural anatomy and maintaining the integrity of tear passage and outflow, rendering excellent cosmetic and functional results. The ancillary procedures used in our study are suggestive of a very specific role for lateral tarsal strip as a sole treatment in correcting various types of eyelid ectropion.Keywords: Lateral Tarsal strip; malposition; paralytic; cicatricial ectropion.
Journal of American Science 2011;7(5):394-405].
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How to write a scientific paper
Title
Author/ Authors name
Abstract
Introduction
Materials and methods
Results
Discussion
Conclusion &
Recommendation
Ackknowledgements
Reffereces (Vancouver
style)
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Refference
The full reference should be formatted according to Vancouver reference system with numbers in the end of the text.
In the text, mention the reference by a superscript number on the end of the line (e.g. 1),
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Vancouver style
Journal articles
1. Heijil A, Peters D, Leske MC, Bengtsson B. Effect of Argon Laser Trabeculoplasty in the Early Manifest Glaucoma Trial. AJO. 2011 Nov;152 (5): 842-8
Book Chapter 2. Dolman PJ. Thyroid associated orbitopathy. In: Mallajosyula S, Editor. Surgical atlas of orbital diseases. 1st ed. Jaypee. New Delhi. 2009. pp. 111-9.
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Referrence
Conference 3. Haider G, Mukti MR, Kadir SM. Evaluation of surgical outcome of LPS resection in ptosis surgery. In: 38th Annual national conferrence of Ophthalmological society of Bangladesh; 2011, March 5-8; Dhaka, Bangladesh.
Webpage
4. National Library of Medicine. Specialized Information Services: Toxicology and Environmental Health. http://sis.nlm.nih.gov/Tox/ToxMain.html (Accessed May 23, 2004).
Thesis
5. Kadir SM. Eyelid Malignancies: A clinico-pathologic study . MS Thesis, Dhaka University: Bangladesh, January 2009.
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Thank you
Is it clear?