5.1 Percentages and odds

Endotracheal intubation (ETI) is a method for maintaining an open airway or as a method for administering certain drugs for ill patients.

ETI is widely used for airway management of children in the out-of-hospital setting, but for many years little evidence was available on the effect of using ETI.

Table 5.1 comes from a study (Gausche et al. 2000) of using different types of endotracheal intubation on children.

Use the table to answer the questions that follow.

TABLE 5.1: Airway management data
Group
BVM group
ETI group
Number % Number %
Normal, no change from baseline 39 (10%) 33 (8%)
No change from baseline 33 (8%) 25 (6%)
Mild disability 20 (5%) 27 (6%)
Moderate disability 6 (1%) 7 (2%)
Severe disability 10 (2%) 6 (1%)
Coma/vegetative 15 (4%) 12 (3%)
Death 281 (70%) 306 (74%)
Total 404 416
  1. Among people treated with BVM (‘ball valve mask’), compute the percentage that died.

  2. Among the people treated with BVM, what are the odds that someone died? Explain which one of the following calculations is correct, and explain what the other calculations compute, and hence why they are wrong.

  3. Among people treated with ETI, the odds that someone died is 2.78. What does this mean?

  4. How many times greater is the odds that a person treated with ETI died compared to the odds that a person treated with BVM died?

References

Gausche, Marianne, Roger J. Lewis, Samuel J. Stratton, Bruce E. Haynes, Carol S. Gunter, Suzanne M. Goodrich, Pamela D. Poore, et al. 2000. “Effect of Out-of-Hospital Pediatric Endotracheal Intubation on Survival and Neurological Outcome: A Controlled Clinical Trial.” Journal of the American Medical Association 283 (6): 783–90.