Study Design

Dr Syeed Mehbub Kadir

Fellow of Orbit & Ophthalmic Plastic Surgery

Sankar Institute of Ophthalmology

Visakhapatnam

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

Study Design

Experimental• Randomized controlled trials• Quasi

Observational

Analytic • Cross sectional• Case-control• Cohort studies

Descriptive• Case report• Case series• Survey

Grimes & Schulz, 2002 (www)

Observational/ Non-interventional study

Descriptive study:

- Case report

- Case series

- Population study (survey) Analytical study:

- Cross-sectional

- Case-control

- Cohort

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

Descriptive Studies: Uses

Hypothesis generating

Suggesting associations

Analytical Studies

Cross-sectional study

Case control study

Cohort study

Cross-sectional Study

Data collected at a single point in time

Describes associations

Prevalence

A “Snapshot”

* 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

Cross-sectional Study

Sample of Population

Smokers Non-smokers

Prevalence of TAO Prevalence of TAO

Time Frame = Present

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

Cross-sectional Study

SMOKING

-

T

A

O

+

- 90

10 90

10

+

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

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

Case-Control Study

Start with people who have a disease

Match them with controls ēout disease

Look back and assess exposures

Retrospective study

Case-Control Study

Patients with CRVO

Patients w/o CRVO

Present (Outcome)

Past (Exposure)

Hypertensive

Hypertensive

Non hypertensive

Non hypertensive

Cases

ControlsComparison

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

Case-Control Study

Patients w POAG

Patients w/o PAOG

Present (Outcome)

Past (Exposure)

RNFL thickness by OCT

RNFL thickness by OCT

Cases

Controls

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

Case-Control Studies: Weaknesses

Cannot measure

Incidence

Prevalence

Relative Risk

Can only study one outcome

High susceptibility to bias

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

Cohort Study

Begin with disease-free patients

Classify patients as exposed/unexposed

Record outcomes in both groups

Compare outcomes using relative risk

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

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

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.

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

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

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

What distinguishes observational studies from experiments?

Ability to control for confounding

Predictor Outcome

Confounder

Examples: Smoking

Male Dysthyroid optic neuropathy

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.

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

Clinical Trial

Study Population

Treatment Group

Control Group

Outcomes

Outcomes

R a n d om i z e

Comparison

Clinical Trial

Patients w Ocular lymphoma

Randomi ze

Ivt Rutiximab

Ivt methotrexate

Comparison

Outcome

Outcome

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

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

Quasi study

The interventional study does not fulfill the following

criteria:

- Randomization

- Controlled

- Blinding

## Chance of Biasness is more

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

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.

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

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

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

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

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].

How to write a scientific paper

Title

Author/ Authors name

Abstract

Introduction

Materials and methods

Results

Discussion

Conclusion &

Recommendation

Ackknowledgements

Reffereces (Vancouver

style)

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),

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. 

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.

Thank you

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