To quote from my book, [The Bayesian Choice][1] (2007, Section 2.3, pp. 63-64) > The Bayesian approach to decision theory integrates on the parameter > space $\Theta$, since $\theta$ is unknown, instead of integrating on > the sampling space ${\cal X}$, as $x$ is observed. It relies on the > ***posterior expected loss*** \begin{eqnarray*} \rho(\pi,d|x) & = & \mathbb{E}^\pi[L(\theta,d)|x] \\ \tag{1} & = & \int_{\Theta} \mathrm{L}(\theta,d) \pi(\theta|x)\, \text{d}\theta, \end{eqnarray*} which averages the error (i.e., the > loss) according to the posterior distribution of the parameter > $\theta$, conditional on the observed value $x$. Given $x$, the > average error resulting from decision $d$ is actually $\rho(\pi,d|x)$. > The posterior expected loss is thus a function of $x$ but this > dependence is not an issue, as opposed to the frequentist dependence > of the risk on the parameter because $x$, contrary to $\theta$, is known. > > Given a prior distribution $\pi$, it is also possible to define the > ***integrated risk***, which is the frequentist risk averaged over the > values of $\theta$ according to their prior distribution > \begin{eqnarray*} r(\pi,\delta) & = & \mathbb{E}^\pi[R(\theta,\delta)] \\ \tag{2} & = & \int_{\Theta} \int_{\cal X} \mathrm{L}(\theta,\delta(x))\, f(x|\theta) \,\text{d}x\ \pi(\theta)\, \text{d}\theta. \end{eqnarray*} One particular appeal of this second > concept is that it associates a real number with every estimator, not > a function of $\theta$. It therefore induces a total ordering on the > set of estimator s, i.e., allows for the direct comparison of > estimators. This implies that, while taking into account the prior > information through the prior distribution, the Bayesian approach is > sufficiently reductive (in a positive sense) to reach an > effective decision. Moreover, the above two notions are equivalent in > that they lead to the same decision. A bit further, I use the following definition for the Bayes risk: > A ***Bayes estimator*** associated with a prior distribution $\pi$ and a loss > function $\mathrm{L}$ is any estimator $\delta^\pi$ which minimizes > $r(\pi,\delta)$. For every $x\in\cal{X}$, it is given by $\delta^\pi(x)$, > argument of $$\min_d \rho(\pi,d|x)$$ The value $$r(\pi) = r(\pi,\delta^\pi)\tag{3}$$ is then called the ***Bayes risk***. [1]: http://amzn.to/2kxykkw