Estimators for a Poisson exposure model
= Estimators for a Poisson exposure model
For $S_r=\sum_i x_i^r$, unweighted least squares through the origin and maximum likelihood give
$$
\widehat\theta_{LS}=\frac{\sum_i x_iY_i}{S_2},
\qquad
\widehat\theta_{MLE}=\frac{\sum_iY_i}{S_1}.
$$
Both estimators are unbiased.