Schwert (1989) writes on page 1117: "The estimator of the variance of the monthly return is the sum of the squared daily returns (after subtracting the average daily return in the month): $$\hat \sigma_t^2 = \sum_{i=1}^{N_t} r^2_{it}$$ where there are $N_t$ daily returns $r_{it}$ in the month $t$. "
Why doesn't he divide $\sum_{i=1}^{N_t} r^2_{it}$ by the number of days in the month $t$, $N_t$? That is, why isn't he calculating the variance of the returns as in: $$\hat \sigma_t^2 = \frac{1}{N_t} \sum_{i=1}^{N_t} r^2_{it} \quad ?$$
