Statistics 227

Homework 7

Due Wednesday, 20 November 1996

• Data on heart-transplant patients' quality of life were collected from patients receiving two different therapies to suppress the immune system (necessary to avoid rejection of the transplanted organ). The table below shows the frequency of severe bruising episodes incurred by patients on azothioprine and on cyclosporine. Write a short paragraph summarizing any conclusions that these data would support.

 
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                        Frequency of Bruises
                            ------------------------------
                               Rarely/    Often/
  Immunosuppresion     Never   Sometimes  Always
       ----------------------------------------------------
  Azathioprine           4         8        19
  Cyclosporine          10        23        11
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• Patients in intensive care often must be intubated, that is, flexible tubing is used to maintain a clear passage for air to reach the lungs. These airways may be inserted through the mouth ("orotracheal intubation") or through the nose ("nasotracheal intubation"). Some patients may have instead a surgical opening made in the windpipe to permit breathing ("tracheostomy"); a breathing tube may be inserted into this opening when present. A serious complication using any of these devices occurs when material that should be swallowed is taken into the lungs instead. This is called "aspiration," and occurs because the mechanical aids to ventilation interfere with the body's usual ability to close the windpipe when material is being swallowed. The data below concern daily observations on patients in a critical care unit. Describe in a short paragraph whether the route of intubation affects the chances of aspiration. Does any particular route put patients at particularly high or low risk of aspiration?

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                             Route of intubation
                  ------------------------------------------
 Aspiration        Nasotracheal   Orotracheal   Tracheostomy   
------------------------------------------------------------
Occurred               24            137            86
Did not occur         116            411           130
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• The data in table 10.24, page 406, of Selvin can be used to explore possible factors that predict a twin birth. Explore the relationship between the predictors parity, age, and race and the outcome "twin birth." Which variable has the greatest impact on the probability of a twin? Write a paragraph summarizing your findings. The data can be found in Selvin Data Sets.

  Hint: What do the following Stata commands produce?

       tabulate twin age
       tabulate twin age [fweight=count]
       logistic twin age
       logistic twin age [fweight=count]