Beta distribution

2 parameters

can only take values in the interval (0,1)

for the beta distribution

$$E(\theta)= \frac{a}{a+b} $$

$$V(\theta)= \frac{ab}{(a+b)^{2} (a+b+1)} $$

$$V(\theta)= \frac{E(\theta)(1-E(\theta)}{a+b+1} $$