You said, "One of the problems of not using NNH or NNT type assessments is that we tend to overestimate prevalence of disease and are poor at calculating risk in our head. The way your statement reads it suggests that your CT scan pick up rate of clinically important ICH in children with minor closed head injuries (that are PECARN negative) is more than than 3% (and up to 10%).This does not sound likely and would not be consistent with the published evidence."
I have to agree with Jay Fisher's approach to risk stratification. For a similar clinical encounter, if the family of a patient who meets low risk criteria based on the PECARN data, enquires about the "worst case scenario," I would have to state that based on a large study of children with TBI, there is 95 % chance that their son's risk of death or operation (CiTBI) may be as high as 1 in 10. The NNH or NNS (number needed to screen) is also very useful, but to me is is most relevant from a population or societal perspective.
On that note, I am struggling with how you arrived at an NNH of 1 in 2,000. There were 61 patients with CiTBI in the high risk group (i.e. any one factor in the prediction rule being positive) & 2 patient's with CiTBI in the low risk group from a population of 6400 subjects in the validation study. The NNS would be closer to ~ 1:100. Besides, you are including just the point estimate in quoting the NNH. To be truly objective, you really need to examine the 95% CI for the NNH.
Unrelated, I thought persistent HA or "severe" mechanism were considered high risk criteria within the decision rule? One could then argue that Lakshmi's patient met both of the above, and cranial imaging would have been warranted???
Very engaging discussion....
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