The regression example (2.1.1 Simple Regression)
states y = β0 + β 1 ∗ x + ϵ
Then in the text below the parameters are called " β0 , β1 , σ2, ϵ , and the mean and variance of x".
And then in the diagram we see σ2x ,σ2y, βy, βyz and μx.
Much easier to follow with one set of conventions rather than three. And where mapping of conventions is necessary, it should be explicit (i.e., "and the mean and variance of x (μx and σ2x respectively) )"