ADVANCED STATISTICAL METHODS: PART 1: …

1 ACS Outcomes Research Course ADVANCED STATISTICAL methods 1 ADVANCED STATISTICAL methods : part 1: introduction TO propensity SCORES IN STATA learning objectives: To understand the use of propensity scores as a means for controlling for selection bias in observational studies of treatment effects. To learn how to create propensity scores apply them in a variety of analytic approaches in STATA. To use propensity scores to evaluate the outcomes of open versus laparoscopic appendectomy in the NSQIP data provided. propensity SCORES IN STATA: Open the dataset and describe the data For this analysis, we will use NSQIP data for patients undergoing appendectomy (2005-2007).

2 This dataset contains 21,475 observations (patients) and 86 variables. The first group (2-56) includes pre-operative patient characteristics and medical conditions. The second group (57-83) includes peri-operative outcomes. The variables morbprob (var #84) and mortprob (var #85) are probabilities of morbidity and mortality, respectively, based on the NSQIP risk models. Finally, the variable treatment (var #86) tells you whether the appendectomy was performed open or laparoscopically. Type the command: describe, number STATA output: Contains data from D:\nbirkmey\Desktop\Desktop\ACS Course 2010\Mark propensity \Appendicitis_Propensity\ obs: 21,475 vars: 90 27 Oct 2010 13:11 size.

3 4,123,200 ( of memory free) ---------------------------------------- ---------------------------------------- --------- variable storage display value name type format label variable label ---------------------------------------- ---------------------------------------- --------- 1. caseid long % Patient ID 2. sex byte % sex Patient Sex 3. race str32 %32s Patient Race 4. race1 byte % race==American Indian or Alaska Native 5.

4 Race2 byte % race==Asian or Pacific Islander 6. race3 byte % race==Black, Not of Hispanic Origin 7. race4 byte % race==Hispanic, Black 8. race5 byte % race==Hispanic, Color Unknown 9. race6 byte % race==Hispanic, White 10. race7 byte % race==Unknown 11. race8 byte % race==White, Not of Hispanic Origin 12. white byte % whitelab White/Non-White Race 13.

5 White1 byte % white==White 14. white2 byte % white==Non-white 15. white3 byte % white==Unknown 16. prncptx str25 %25s Principal CPT ACS Outcomes Research Course ADVANCED STATISTICAL methods 2 17. cpt str5 %5s CPT code 18. inout byte % inout Inpatient/Outpatient Status 19. age byte % Patient Age 20. operyr int % Year of Operation 21.

6 Height byte % Patient Height 22. weight int % Patient Weight 23. bmi float % BMI 24. bmi40 float % Morbid Obesity 25. bmicat byte % 4 quantiles of bmi 26. diabetes byte % diabetes DM/oral or insulin 27. diabet~1 byte % diabetes==No 28. diabet~2 byte % diabetes==Oral Med 29. diabet~3 byte % diabetes==Insulin 30. smoke byte % yesno Current (Within 1 YR) Smoker 31.

7 Etoh byte % yesno Current (Within 2 Weeks) Drinker (>2 per Day) 32. dyspnea byte % dyspnea Dyspnea 33. dyspnea1 byte % dyspnea==No 34. dyspnea2 byte % dyspnea==Moderate Exertion 35. dyspnea3 byte % dyspnea==At Rest 36. dnr byte % yesno DNR Status 37. fnsta~s2 byte % fnstatus2 Functional Status Prior to Surgery 38. fnsta~21 byte % fnstatus2==Independent 39. fnsta~22 byte % fnstatus2==Partially Dependent 40.

8 Fnsta~23 byte % fnstatus2==Totally Dependent 41. hxcopd byte % yesno History of Severe COPD 42. ascites byte % yesno Ascites 43. hxchf byte % yesno CHF within 30 days 44. hxmi byte % yesno MI within 6 mths 45. hypermed byte % yesno HTN requiring medication 46. dialysis byte % yesno On dialysis pre-op 47. pregna~y byte % yesno Pregnant at time of surgery 48. rupture byte % Rupture 49.

9 Emergncy byte % yesno Emergency Case 50. asa byte % asa ASA Class 51. asa1 byte % asaclas==1-No Disturb 52. asa2 byte % asaclas==2-Mild Disturb 53. asa3 byte % asaclas==3-Severe Disturb 54. asa4 byte % asaclas==4-Life Threat 55. asa5 byte % asaclas==5-Moribund 56. asa6 byte % asaclas==NULL 57. tothlos int % LOS 58.

10 Supinfec byte % yesno Superficial surgical site infection 59. wndinfd byte % yesno Deep Incisional SSI 60. orgspc~i byte % yesno Organ Space SSI 61. dehis byte % yesno Wound Disruption 62. oupneumo byte % yesno Pneumonia 63. reintub byte % yesno Unplanned Reintubation 64. pulembol byte % yesno PE 65. failwean byte % yesno Ventilator>48 Hours 66. renainsf byte % yesno Progressive Renal Insufficiency 67.