Once again -- 10-40% is not 50/50 chance. This all started with me asking for the factual basis of 50/50.
Whenever I have seen data based estimates as high as 90%, it is from table that also includes a lot of 0% entries.
What you consider credible depends on what you are willing to believe. 10%-90% is a rather wide range. Was David Howman talking about men's distance running, or the London Olympics? Recall that the London 2012 Olympics was 26 different sports, of which "Athletics" is but one, which itself includes sprint, fields, and race-walking.
I don't know what facts Victor Conte knows about distance running. I'm also not aware of who Ann Richards is. Maybe you mean Renee-Anne Shirley? Likewise, what does a Jamaican whistleblower know about distance running performance? I'm interested in facts, not the beliefs of people. I would generally agree with "it is present in all sports and across all countries at the elite level, with the collusion of sports governance bodies", but find it too general to suggest one distance running performance is more suspicious than any other.
The question isn't whether Kenya has a doping problem, or whether sports or countries are not immune. You said 50/50 chance. It already makes a big difference compared to 1 in 3 or 1 in 4. Then we can say 2 in 3 or 3 in 4 are clean. But why stop there? These threads are dominated by EPO suspicion. Why not use the Sunday Times reporting of 1 in 7, or 1 in 9, or 1 in 12.5, or 1 in 14, depending on the country?