Of course that anecdotal evidence is valuable! It just depends on the pool it's been taken from. Canary breeding and husbandry evolved to where it is today from mere anecdotal references BUT we are talking about thousands upon thousands of people, hundreds of thousands of birds and hundreds of years accumulating and sharing experiences. Just as an example, I always 'knew' about the solar schedule, even way when I was a young girl and several decades before it was considered for parrots because anybody who bred canaries knew that they needed 13.5 to 14 hours of light to breed well. Canary breeders did not know the why or how of it but they knew this to be so and anybody who 'experimented' with it found it to be a fact creating, thus, a consensus about it.
I, myself, rely on anecdotal evidence and my own observations whenever there is no empirical data. But, when it comes to clipping, there IS empirical data on the danger of it and the anecdotal evidence is not only a mixed bag with people's experiences been both for as well as against (meaning absolutely no consensus) but also of only a few years and a few people with, usually, one or two birds -and that is what makes it unreliable. We are really not good observers of what is close to us (think of all the parents that were caught by surprise by the fact that their kids were doing drugs or all the neighbors that describe serial killers as 'good people') - and this is the reason why scientists conducting studies are not supposed to regard the objects of their studies as nothing but that. Because when we have any kind of bond with another being, our objectivity disappears and we only see what we want to see.
Now, much has been made of the fact that there are no studies on pet parrots mild clipping (and there aren't any per se) BUT there are loads of studies done on lots of things that are related as well as one that represents exactly what clipping does: increased wing load (the mathematical relationship between the size of the wing -as in the total area that 'resists' or 'moves' the air, think of a fan, the larger the fan, the more air it moves- and the weight of the bird's body) as well as what the wing aspect ratio (which is, basically, the actual shape of the wing because it's the mathematical relationship between the width and the length of the wing- and the shape!) does to flight. The studies are not on parrots and few use clipping, most are on birds that were either made to carry more weight (through weighted harnesses) or on birds that are naturally heavier (as in when a hen is forming an egg, for example) but every single study shows that when the wing load is higher (less wing to more weight -as when we clip) the take-off is slower, that slower take-off means more predation and that birds that have a higher wing load feel more vulnerable (see below).
Ergo, even if we leave aside all considerations of personal preference or philosophy on the part of the keeper, and/or physical and/or emotional consequences for the bird, if one goes down to the 'safety' issue, which is, by far, the number one reason people give for clipping, there are, indeed, scientific studies that do prove that a clipped bird (higher wing load) will be more in danger from predators than a fully flighted bird. So much so, that, in the wild, when birds are exposed to an increase in predation, they would lose weight in order to reduce the wing load and increase take-off speed!
See these:
https://www.researchgate.net/publicatio ... al_breederhttp://link.springer.com/chapter/10.100 ... 9-6421-2_1http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3138777/http://www.rug.nl/research/portal/files ... vdHout.pdfhttp://journals.plos.org/plosone/articl ... ne.0022352In these two, they actually clipped birds:
https://www.researchgate.net/publicatio ... ation_riskhttp://beheco.oxfordjournals.org/conten ... 4.full.pdf