Response to “Comments on ‘How Fragile Are the Results of a Trial? The Fragility Index’ by Dettori and Norvell”

We thank Nathan Evaniew for rightly pointing out that the example in Table 1 of our article reviewing the fragility index ¹ incorrectly changed the number in the treatment arm having the larger number of events. The calculation for the fragility index describes how many patients are required to have a different outcome within the group with the fewest number of events to make a study’s result not statistically significant. Though the results of the illustration remain the same, Table 1 should be corrected as follows:

Table 1.

Fragility Index Calculation Example Using Data Comparing Fusion of the Lumbosacral Spine Between rhBMP-2 and Iliac Crest Bone Graft (ICBG).

	rhBMP-2	ICBG	P
Original results	186/194	151/169	.023
Step 1	186/194	152/169	.036
Step 2	186/194	153/169	.055

We appreciate the opportunity to correct this oversight.

Joseph R. Dettori, PhD Daniel C. Norvell, PhD Spectrum Research, Inc, Steilacoom, WA, USA