Tell me, why was this subject lost to follow-up?

So, I’m reading a randomized controlled trial comparing two common methods of wart removal : duct tape and cryotherapy (Focht DR III, Spicer C, Fairchok MP. The efficacy of duct tape vs cryotherapy in the treatment of verruca vulgaris (the common wart). Arch Pediatr Adolesc Med. 2002;156:971-974). No, I didn’t know you could use duct tape for this purpose, either— although I gotta say, I’m not too surprised. I mean, what can’t that stuff do? Anyway, as is customary in this sort of paper, the authors begin their results section by talking about the study period and how many subjects they ended up with:

From October 31, 2000, to July 25, 2001, 61 patients were enrolled in the study. Nine patients, 3 from the duct tape group and 6 from the cryotherapy group, were not available for follow-up and were not included in our analysis.

So far, pretty unremarkable. But dig what comes next:

One patient enrolled in the duct tape arm lost his study wart in a trampoline toe-amputation accident and was also not included in our analysis.

Yikes. As tragic as that is, you just know that the authors had fun figuring out how to word that for the writeup…

It turns out that duct tape was definitely more effective than cryotherapy: 85% of the duct tape patients' warts were completely resolved, whereas only 60% of the cryotherapy patients' were (chi-squared p-value of 0.05, which is, if not exactly significant, close enough that it implies that they’re probably on to something good—– especially given the limited sample size and some of the study limitations as noted in their discussion). The time-to-resolution was comparable between the two treatment groups, although the authors note anecdotally that the warts in the duct tape arm of the study that didn’t resolve by 14 days were unlikely to suddenly change course and resolve after that point.

Of course, the study had a few interesting statistical problems, most importantly, that the authors only reported point estimates rather than proper risk or odds ratios with confidence intervals (pointed out in a follow-up letter to the editor ). I didn’t actually catch this problem on the first read-through, although I did notice that the authors sort of glossed over their analysis— they probably figured that with results like theirs, duct tape was so clearly superior to cryotherapy that it wasn’t necessary to belabor the point statistically. In this particular case, I can see where they’re coming from, but still wish that they’d gone into more detail— it’s one of those “good form” things, like stopping at a four-way stop in the middle of nowhere even when there’s nobody around. Confidence intervals keep us all honest.