Sochacki et al. write as follows in recent study criticizing sham-controlled studies in orthopaedics:
Additionally, two studies in this systematic review were performed in Finland. Unfortunately, any study investigating an intervention (e.g. surgery) on individuals born and raised in Finland cannot be extrapolated to the rest of the world. Finns embrace sisu, a special form of courage, grit, and determination. This grit applies to any medical condition that is electively evaluated and treated, including subacromial shoulder pain and degenerative knee pain, adding a confounding source of selection bias to these investigations.
“Suomi mainittu! Torilla tavataan!” we Finns might say. This is certainly an interesting proposition.
Let´s assume that sisu truly exists and it can be quantified in some manner. Firstly, it is evident that not ALL Finns embrace sisu. And even if each and every Finn did so, the amount of sisu certainly varies from individual to individual. Sochacki et al. state that sisu adds “a confounding source of selection bias” to sham-controlled studies performed in Finland. In another words sisu is a collider as shown below.
If sisu was truly causing selection bias and being a collider, it would be favoring meniscectomy. Before patient can undergo a meniscectomy he or she must see a physician who refers him or her to an orthopaedic surgeon. It is very likely that those Finns with low sisu would be those who gets referred to orthopaedic surgeon because those Finns with knee pain and with true sisu won´t see their physician in the first place. That would mean that the patients included in these sham-controlled studies would be those most susceptible for benefit after meniscectomy if there was any benefit at all to achieve. That said, I don´t agree with Sochacki et al. with their statement about selection bias.
Confounding by sisu in some another way does not either seem plausible. I´d refer to excellent piece by Darren Dahly who carefully explains about confounding, prognostic variables and RCTs in general. He writes among other things:
… people start to believe in a boogeyman called infinite confounders, which leads them to mistakenly discount the value of randomization. It’s the idea that even with randomization that there could always be some kind of strong prognostic factor that we didn’t measure that is disproportionately distributed across the trial arms that wrecks the validity of our results. Taken to the extreme, you even have people arguing that the trial arms should be very tightly “balanced” for every possible characteristic to make valid inferences about an outcome (e.g. this obscene paper in PLOS One).
If sisu was a prognostic factor, adjusting for it would not probably offset the results of sham-controlled studies. Adjusting would make the results just more precise. So, again, sisu can´t be seen as valid source of true confounding.
Sochacki et al. continue:
It is this grit observed in sisu and hygge that may objectively account for differences in absolute and relative values of patient-reported outcomes in all of the placebo-controlled studies analyzed in this review from these studies (4 of 7), but were not measured.
As said, sisu might be a prognostic factor, and if so, it can be accounted for by an adjustment. I don´t understand how sisu or hygge could account for differences in absolute and relative values of PROMs. This would mean that sisu and hygge somehow interact with treatment given. But in randomized trial this is just impossible.
Until further evidence, sisu, if measured, should be treated as any other prognostic factor which can be handled in the analysis of RCT results. It seems that sisu is a big thing in sports medicine, so I look forward to validated tools to measure sisu or hygge in sports surgery setting!