# Parameters in distributions

When it comes to representing certain continuous distributions like Gamma or Exponential, some books use the notation (1/theta)×e^(-x/theta), while other books use the notation theta×e^(theta×x) (this is for Exponential dist). Why this difference in notation? Does it make any difference no matter which notation we use? P.S: my teacher said something along the lines of the former notation being correct, because the latter notation poses problems in higher statistics.I didn't quite get it.

It's a trivial difference. The first is called the scale parameter whereas the latter is rate parameter. The density function is the same. Just the notation changes. For example, you have a density $$f\left(x\right) = 2e^{-2x}, \quad x>0.$$ Then, you can use either notation \begin{align*} &\operatorname{Exp}\left(2\right)\;\text{(rate)} \\ &\operatorname{Exp}\left(1/2\right) \; \text{(scale)} \end{align*} Once you know which one the author uses, the density will be the anchor that connects both. There's really no importance in which one you should use. You can choose whatever is comfortable.