[xtacy]

Maybe, but there is another, perhaps simpler hypothesis: Both the transistor count and life expectancy increase with time.

One way to verify one or the other is to look at a linear hypothesis:

    States: LifeExp, Transistors, Time
    Structural Equation Model [1]:

Model 1:

    LifeExp ~ Time + Transistors + noise_exp_1
    Transistors ~ Time + noise_trans_1

(The 2nd equation means that: Transistors(t) = a * t + noise, and you try to estimate "a" from the data.)

vs Model 2:

    LifeExp ~ Time + noise_exp_2
    Transistors ~ Time + noise_trans_2

If model 2 has more predictive power of LifeExp than model 2 (i.e., noise_exp_1 is lower than noise_exp_2), then according to _this_ model, Transistors causally affects LifeExp. However, this model is way too simplistic and doesn't incorporate other causal paths, such as the one you describe (Transistors -> Computing -> DiagnosticRate -> ...)

[1] http://en.wikipedia.org/wiki/Structural_equation_modeling

[zealon]

Math is not my field of expertise, but I think I get your point. My point was based on a social and economics perspective. I think these other causal paths are fundamental, because they are empirically verified (computing power vs health and life quality).