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Suppose for each $x\in[0,1]$ I have random variable $f_x$ defined on $(\Omega_x,\mathcal{F}_x,\mathbb{P}_x)$ where $f_x \sim \operatorname{Ber}(x)$; i.e. $f_x=1$ w.p. $x$ and $f_x=0$ w.p. $1-x$.

If I understand this post correctly, can construct a probability space $(\Omega,\mathcal{F},\mathbb{P})$ as an infinite product space of the $(\Omega_x,\mathcal{F}_x,\mathbb{P}_x)$ for all $x\in[0,1]$, and I also believe that $f$ will be a random variable on $(\Omega,\mathcal{F},\mathbb{P})$.

Based on my application, I would like to compute, $$ \mathbb{E}_{\Omega} \left[ \int_0^1 f(x) dx \right]. $$

However, since $f_{\omega}$, $\omega\in\Omega$ is the indicator function of some set on $[0,1]$, it seems possible that $f$ may not be Lebesgue integrable.

Is there another way I can interpret $\int_0^1 f(x) dx$ to avoid this? (i.e. not Lebeguse).

Otherwise, is it possible to compute $\mathbb{P}[ \{f : f \text{ is not Lebeguse measurable} \} ]$?

Perhaps another possible workaround for me would be to define my product space on $[0,1]\cap (\beta\mathbb{Z})$ where $\beta$ is very small so that I can use a sum to approximate the integral?

  • You are correct that $f$ needn't be pathwise integrable in any meaningful sense. This is basically the same issue that causes white noise to not be a sensible stochastic process; indeed if your process even had measurable paths then you could use the probability integral transformation to convert it into white noise. – Ian Feb 07 '20 at 17:36
  • Is there any fix? In this case it seems like $f(\omega)$ has a lot more structure than white noise. On the wikipedia page for white noise in the section on Continuous-time white noise they give an integral similar to what I have, but no references. – overfull hbox Feb 07 '20 at 19:42
  • My point was that if you make them independent by defining them through the product structure, then actually they have pretty much the same structure as white noise. They're not identically distributed, but that doesn't really matter. You're still going to have "oscillation everywhere", and in a way that can't be fixed by just excluding a Lebesgue-small set. – Ian Feb 07 '20 at 21:22
  • I guess what I mean is are there well defined integrals on this type of thing? – overfull hbox Feb 07 '20 at 21:47
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    The answer is basically no, not pathwise. – Ian Feb 08 '20 at 00:13

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