Also posted over at Rogue Medic (now at EMS Blogs).
Continuing from Part I.
After assessing what it is that the abdominal pain patients want/expect from a visit to the ED (Emergency Department), they move on to part 2.
Second, we attempted to assess patients’ understanding of relative radiation exposure by asking them to compare the amount of radiation exposure from one abdomen-pelvis CT to increasing numbers of 2-view chest radiographs (standard posterior-anterior and lateral chest series).
And a graph of the responses is here. I added a red bar as an estimate of the responses that were not given because the patients thought that the radiation from a CT is less than the radiation from an X-ray.
When presented as 50 out of 121 who did not answer the question, it seems to be a large percentage, but it is only 50 out of about a thousand patients who did answer the question. Not a large percentage.
The authors included a footnote to the study that produced the numbers they are relying on, but they never specifically cite the X-rays per CT number from that study. This is probably because that study did not produce any simple answer. There is a lot of interpretation of the many factors involved in the study. Even then, the idea that the result can be presented as any simple answer would be misleading.
The simplest answer is in the response of those authors to criticism of their methods.
The concern is that radiation doses from CT are typically 100 times those from conventional x-ray examinations such as chest x-rays or mammograms and that there is now direct epidemiologic evidence of a small but significant increase in the risk of cancer at CT doses.1-3 Because CT is such a superb diagnostic tool and because individual CT risks are small, the CT benefit–risk balance is generally by far in the patient’s favor.
Is that with any defined size of the error bars?
Because CT is such a superb diagnostic tool and because individual CT risks are small, the CT benefit–risk balance is generally by far in the patient’s favor.
This does not appear to be the message being communicated by the authors of the study I am looking at. When we are dealing with any risks, we should understand the risks, but it does not help to exaggerate the risks.
Again, would physicians do much better in answering the same questions?
Are the answers in this study? Or does this muddy the waters?
 Patient perceptions of computed tomographic imaging and their understanding of radiation risk and exposure.
Baumann BM, Chen EH, Mills AM, Glaspey L, Thompson NM, Jones MK, Farner MC.
Ann Emerg Med. 2011 Jul;58(1):1-7.e2. Epub 2010 Dec 13.
PMID: 21146900 [PubMed - indexed for MEDLINE]
 Computed tomography–an increasing source of radiation exposure.
Brenner DJ, Hall EJ.
N Engl J Med. 2007 Nov 29;357(22):2277-84. Review. No abstract available.
PMID: 18046031 [PubMed - indexed for MEDLINE]