Over the couple of years I've been lurking here, I've enjoyed a lot of threads, in which various people expressed an opinion that one decompression strategy is believed to be better than or as good as another. The way I usually like to think about claims that "X is better than Y" is, to try to justify or reject them on the basis of some sort of measurement. I would ideally want to think of some metric of "badness", such as the "% of injuries among divers" (for some definition of "injuries" and some criteria of selecting divers) that we can use to determine, independently, how bad X and Y are. Upon finding that badness(X) < badness(Y), we would then feel more comfortable accepting the claim that X is better.
I wonder what sorts of metrics exist out there that are widely believed to be meaningful, and that could be used to compare different decompression strategies.
The various metrics I've heard about so far seem to fall onto a spectrum.
On one end, we have the "% injuries" sort of metrics. These are the most meaningful, since, well, they talk directly about injuries, which is what we all ultimately care about. From what I understand, they seem to suffer from a general scarcity of data. When findings based on such metrics are reported, people inevitably bring concerns that the size of the population may have been too small, or that not all important factors were controlled for, or that the dive profiles were not sufficiently representative, etc. My understanding is that in order to extrapolate anything statistically significant out of those studies at all, a lot of assumptions have to be made that are later inevitably called into question.
On the other end of the spectrum, we have purely synthetic sorts of metrics, such as % tissue saturation in some compartment or another, that are not even based on measurements of the diver's body. There is no shortage of data, but not surprisingly, some controversy over whether these metrics are even measuring anything we care about, and a lot of ambiguity (which tissue compartment is more important?).
In the various posts I've read on the topic, often the choice/design of the metric itself seems to be based on assumptions that different models do not necessarily agree on (like, the extent to which tissue saturation is a factor in predicting the risk of an injury). Sometimes, it sounds like one faction "proving" that the Christmas holidays are, of course, vastly superior to the Easter holidays, on the basis of the fact that they are in December.
In-between these extremes, there are apparently some metrics, like those based on Doppler measurements, that are based on some real, physical assessments of the diver, but where there is some controversy over whether the symptoms being measured have any real significance (in the sense that they are somehow correlated to the risk of an injury).
So, what other metrics are out there? What's the rationale behind choosing them? How much agreement exists that they're meaningful? What do the critics say? Thanks in advance for all replies.
I wonder what sorts of metrics exist out there that are widely believed to be meaningful, and that could be used to compare different decompression strategies.
The various metrics I've heard about so far seem to fall onto a spectrum.
On one end, we have the "% injuries" sort of metrics. These are the most meaningful, since, well, they talk directly about injuries, which is what we all ultimately care about. From what I understand, they seem to suffer from a general scarcity of data. When findings based on such metrics are reported, people inevitably bring concerns that the size of the population may have been too small, or that not all important factors were controlled for, or that the dive profiles were not sufficiently representative, etc. My understanding is that in order to extrapolate anything statistically significant out of those studies at all, a lot of assumptions have to be made that are later inevitably called into question.
On the other end of the spectrum, we have purely synthetic sorts of metrics, such as % tissue saturation in some compartment or another, that are not even based on measurements of the diver's body. There is no shortage of data, but not surprisingly, some controversy over whether these metrics are even measuring anything we care about, and a lot of ambiguity (which tissue compartment is more important?).
In the various posts I've read on the topic, often the choice/design of the metric itself seems to be based on assumptions that different models do not necessarily agree on (like, the extent to which tissue saturation is a factor in predicting the risk of an injury). Sometimes, it sounds like one faction "proving" that the Christmas holidays are, of course, vastly superior to the Easter holidays, on the basis of the fact that they are in December.
In-between these extremes, there are apparently some metrics, like those based on Doppler measurements, that are based on some real, physical assessments of the diver, but where there is some controversy over whether the symptoms being measured have any real significance (in the sense that they are somehow correlated to the risk of an injury).
So, what other metrics are out there? What's the rationale behind choosing them? How much agreement exists that they're meaningful? What do the critics say? Thanks in advance for all replies.
