In the "Model Equation $X _ { y } = \mu _ { i } + \varepsilon _ { y } { } ^ { \prime } s$

Essay

In the "model equation" $X _ { y } = \mu _ { i } + \varepsilon _ { y } { } ^ { \prime } s$ are assumed to be independent and normally distributed random variables with mean of 0 and standard deviation of $\sigma$ for every i and j. Then the mean and variance of $X _ { y }$ are __________ and __________, respectively.