As readers of this blog will know, one of my favourite themes is sampling bias. I have recently been trying to explain to Geo that there is not necessarily any great "significance" in the fact that a few old geologists found a few erratics from a certain area in another area where there happened to be a few ploughed fields which were easy to examine. On that basis they described what they found, thereby inviting other geologists to go and have another look in the same place, some 70 years later -- that, in a grotesque sort of way, invested the location with even more "significance" simply because it was mentioned by name...........
But actually, our concentration on this particular site is entirely illogical and artificial........ it may well be that there is a far more significant site one field away, or a kilometre away, or ten kilometres away, which nobody has yet discovered or got round to looking at........
This is a quote from the Wikipedia page on sampling bias:
An example of selection basis is called the "caveman effect." Much of our understanding of prehistoric peoples comes from caves, such as cave paintings made nearly 40,000 years ago. If there had been contemporary paintings on trees, animal skins or hillsides, they would have been washed away long ago. Similarly, evidence of fire pits, middens, burial sites, etc. are most likely to remain intact to the modern era in caves. Prehistoric people are associated with caves because that is where the data still exists, not necessarily because most of them lived in caves for most of their lives.
I have previously admitted to sampling bias myself, when in my D Phil thesis I gave great importance to a site called Ogof Golchfa, thinking it to be unique and hugely important, whereas when I went back many years later I realised that there was an even better (and more important) site just round the corner, which I had entirely missed. Why had I missed it? It might have been covered with brambles at the time, or it may have been pouring with rain when I walked past it, or it may only recently have been revealed by a rockfall.
On the same basis I have expressed concerns about the incredibly detailed provenancing by Rob Ixer and Richard Bevins of the "foliated rhyolites" from Craig Rhosyfelin to within a few metres of one particular sampling location. As I have explained before on this blog, I am not sure that you can do that, unless you have sampled several hundred sampling points on a detailed and very tight grid, across a large area. And your sampling is in some way biased towards the places where you have rock outcrops at the surface. In other words, the provenancing conclusion may be down to sampling bias rather than reality. So although their geology is highly impressive, I retain a degree of doubt and reserve judgment on the conclusions reached.
In the archaeological field, we see over and over again that a site or group of sites may be interpreted as belonging to some great cultural complex, only for the thesis to be overturned as new discoveries show wider distributions than anticipated, or even larger and more complex associations of features elsewhere. In Pembrokeshire, for example, we have suspected for many years that the distribution of cromlechs or standing stones (as we see them today) may have no geographical or cultural significance -- it may simply be that those features in the roughest areas have survived better, while features in the lowlands which have been heavily used for agriculture over the past few centuries have been flattened or simply removed because of their "nuisance value." And those features that have survived in the uplands have not survived because they were venerated in any way, or even because they were erected in "sacred places" -- but because in recent centuries they were not particularly in anybody's way, so that nobody could be bothered to remove them.