Number Needed to Treat

In this article on Science Based Medicine, Dr. Harriet Hall sets out the significance of the Number Needed to Treat (NNT) as a measure of the benefit of a medical intervention (drug, procedure, or other therapy).  In brief,  the NNT represents the total number of patients that must be treated for one person to benefit (on average, of course).  Not too surprisingly, it turns out that most patients do not benefit (or do not benefit much) from most therapies.  Hall uses the example of statins for heart disease, explaining that "60 people without heart disease have to be treated with statins for 5 years to prevent one heart attack. For people who already have heart disease, the NNT to prevent one non-fatal heart attack is 39, and the NNT to save one life is 83."  That is actually a fairly low NNT, which makes statins a good choice for people with any risk factors at all.

Hall's article links to a fascinating website that provides the NNTs, as well as the associated risk factors, for hundreds of therapies, arranged by medical specialties from cardiology to urology. It also lists the studies on which the NNTs are based.  I pulled up a couple of examples at random:  Antibiotic treatment for acute sinusitis has an NNT of 15; zinc for the common cold has an NNT of 5; aspirin to prevent a first heart attack or stroke has an NNT of 1667, and an NNT of 50 for those with known heart disease or a prior stroke.  Most interesting are some of the better known screening procedures.  PSA screening for prostate cancer has an infinite NNT (that is, "none were helped," in the sense of statistically reduced mortality); while CT scanning for lung cancer has an NNT of 217 (among high-risk subjects).

I am not aware of any comparable studies for legal procedures, but some can be figured pretty easily.  The NNT for certiorari petitions, for example, seems to be somewhere around 100.  But what is the NNT for the common motions in trial courts, such as motions to suppress (in criminal cases) or summary judgment (in civil cases)?

 

Comments

[Jack Chin]

Super-interesting post. But (as I am sure you well know) lawyers file motions for reasons in addition to the hope of winning the motion; to educate the court about the case, communicate with the other side, get the client ready to take the plea, etc. In the case of cert petitions, filing continues the AEDPA clock. I suspect that some of this (i.e., multiple goals or potential benefits) is also true in different ways with respect to medical interventions.

[Matthew Reid Krell]

NNT for summary judgment motions is one, because the purpose is not to resolve the case but to bill for preparing the motion for summary judgment.