I was speaking about the researches for understanding the effects of doping, not about the validity of blood values, if investigated in longitudinal way.
While for any person, from the sedentary till the WR holder, we can build a Biological Passport based on several blood tests (not less than 10) carried out in a logic period of time (for example one year) looking at the fluctuation of the values, and the validity of the process doesn't depend on the value of the person in some specific event (so, probably, if we want to build a BP for normal people, we can discover many are doped without knowing... thank to all the medicines and supplements they take, not because they need, but because easily influenced by the heavy publicity bombarding continuously the brain of the most part of persons..... but this is another story), when we speak about "researches" looking at the effects of doping, ALWAYS we see that the subjects are part of a general population, very far from the specific class of top athletes.
I never become tired to explain that for speaking about effects of doping we MUST, before, to know the effects of training.
And training is not something "generic", but has very specific features.
What does mean "well trained" for a Group of athletes, generically called "elite" ? Is 40 km in 3 hours a workout producing on the body the same physiological effect, in some athlete with 2:50 of PB and in another athlete with 2:05 of PB ? Is 10 x 400m in 72" an example of "good specific training" for an athlete with PB of 16:00 in 5000m, or for Mo Farah ?
Accepting the fact that the physiology works in the same way for everybody, for increasing the personal ability to perform in some direction, how much is the influence of different training (as volume and intensity) or/and of the assumption of some PED, in order to modify the physiology itself for achieving more important results ? And how much is the influence of the COMBINATION of training and PEDs ? And how much the increase of quality and volume of training can reduce the importance of PED's, till cancelling completely the possibility of further improvements due to the PED assumption ? Or, on the contrary, how much the increase of doping can limit the effects of training (so more doping = less training, and also increasing training the athlete can't improve, because the development of his qualities depends more on the pharmacs he takes than on the level of his training) ?
Not every doping is the same, and putting in the same pot the assumption of steroids and of EPO and derivates is a great mistake. If NEVER (sorry for J.O.) it's possible for athletes using roids to reach the same level of muscle strength using clean training only (so in this case the effect of PEDs assumption on the final performance is evident, how the WR in throwing and all the events based on muscle strength clearly shows : no WR after 1988), ALWAYS it's possible to reach the same maximal level of competitivity in the sport of endurance not using external equipments (such as skies, or bikes), particularly running and swimming long distances, ONLY with proper training and a right modulation between training loads and recovery.
For doing this, we need to know which effects the training of top athletes can have on their physiology. And I'm quite sure that NOBODY about all the scientists involved in antidoping have real data about the effects of training of the best athletes in the world, because they don't know what athletes do, and don't have possibility to test with continuity these athletes during their periodization.
For a real research, there is one system only : to ask many of the top in the World to control their blood values periodically (for example, every 3 weeks) at charge of WADA or some other Agency, during all the season, putting the values in relation with the training period and the current shape of the athletes. This for knowing and understanding the effects of training.
And this MUST be the first step, before speaking about effects of doping.