valemid.md 480 B
$$
{p = \frac{fatalities_current_year + fatalities_previous_year}{population_current_year + population_previous_year}} {\qquad\qquad} {\left( 1 \right)}
$$
$$
z = \frac{{\left( {\frac{fatalities_current_year}{population_current_year}}-{\frac{fatalities_previous_year}{population_previous_year}} \right)}}{\sqrt{{p}{(1-p)}{{\left( {\frac{1}{population_current_year}}+{\frac{1}{population_previous__year}}\right)}}}} {\qquad\qquad} {\left( 2 \right)}
$$