Supplement to Chapter on Causal Controls

Presentations

  • Step by step guide to constructing causal control charts Slides►

Assignments

Question 1: There are many reasons for excessive boarding times in emergency rooms.  The following data shows the simulated experience of a hospital.  For each time period, we show the number of excessive boarding and total patients examined.  These numbers are divided into 4 strata each corresponding to presence of alternative reasons for backup; in particular whether there was image or hospital-bed back up present.  The pre-intervention period corresponds to before hiring additional personnel for the emergency room.  The post intervention refers to the period after hiring,  Create a control chart to examine if the addition of new personnel in the emergency room has led to decline of excessive boarding times. Data► Excel Example►

  Month Pre-Intervention Controls Post-Intervention Cases
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Total Examined None 3 6 19 27 27 3 1 27 19 17 19 4 27 19 3 28 24 21 13 4 17 18 28 18 18
Image Backup 21 22 4 22 0 5 16 9 23 27 6 11 3 21 27 21 2 25 8 24 0 29 19 16 28
Bed Availability 1 1 2 1 2 0 5 8 1 2 9 11 17 1 10 2 4 11 12 14 12 2 17 13 2
Image & Bed Backup 4 18 28 28 20 18 7 18 19 13 24 26 8 26 19 4 24 17 0 26 12 29 20 16 0
Excessive Boarding None 0 0 2 1 3 0 0 3 1 2 2 0 3 1 0 4 2 2 0 0 1 1 3 1 2
Image Backup 10 10 1 6 0 2 6 2 9 7 3 6 1 22 60 35 2 57 17 41 0 42 45 23 56
Bed Availability 0 0 0 1 2 0 1 3 0 1 6 7 8 0 7 1 1 4 11 7 10 1 12 12 0
Image & Bed Backup 5 18 18 28 20 18 7 10 23 13 11 20 7 26 19 2 15 17 0 26 14 16 20 9 0

Using weighting procedures, the following control chart is obtained:

Causal Control Chart

Question 2:  Estimate the effect of election of president Trump on healthcare stock of Humana Inc.  Election of president Trump was a surprise to many.  After his election, stock prices may reflect both his election as well as the stock's historical patterns. President Trump had promised to repeal and perhaps replace Obama Care. Humana Inc. was one of the insurers who was active within Obama Care. It eventually dropped out of the insurance markets months later; but at the time it should have been affected by the uncertainty about future of Affordable Care Act (Obama care). Examine the price of Humana's stock prices 2 months before and 2 months after the election; did the election make a difference in percent of days the stock went up? Complete the analysis for every 6 days the market was open. Repeat the analysis and this time control for the Nasdaq index fund (as a surrogate of general economy) and Standard & Poor Healthcare Sector index (a surrogate for changes in the healthcare industry). After controlling for these two alternative explanations, did the election still affect percent of days stock went up?  Data► Chihiro's Slides► Chihiro's write up► Excel

More

  • Stratified covariate balancing PubMed► More►
  • Causal analysis of emergency department delays PubMed►
  • Judea Pearl's home page on causal modeling More►