Study design


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Study design

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