The standard error of an fertility ratio, estimated number of children ever born per one thousand
women x and estimated number of women y, is approximately equal to x times the square root of
(begin parenthesis) the a parameter plus (begin parenthesis) the b parameter divided by (begin
parenthesis) x times y (end parenthesis) (end parenthesis) plus (begin parenthesis) the c
parameter divided by (begin parenthesis) one thousand times y (end parenthesis) (end
parenthesis) (end parenthesis).