Even though the Mormon church doesn’t actually report the number of members leaving the church, it’s still easy to prove apostle Cook wrong with simple arithmatic and an appeal to common sense. First the arithmatic:
Members this year = members last year + children + converts – members lost
Solving for members lost yields:
Members lost = members last year – members this year + children + converts
Members lost in 2013 = members 2013 – members 2014 + children 2014 + converts 2014
= 15,082,028 – 15,372,337 + 116,409 + 296,803
Doing this for every year since 1975 (when the church started reporting numbers of children and converts) yields the following chart:
1. Deaths and resignations are both increasing;
2. Deaths or resignations are increasing while the other remains constant;
3. Deaths are increasing more than resignations are decreasing;
4. Resignations are increasing more than deaths are decreasing.
According to the United Nations, death rates around the world have decreased by about 20% between 1975 and 2015. This decrease is less dramatic in the US, where most Mormons live, but still a decrease of about 8%. In South America, where most Mormons outside the US live, the mortality decrease is even 30%.
That leaves only option 4: resignations are increasing at a rate that not only offsets the 8-30% mortality decrease in Mormonism’s primary markets but actually doubles the rate at which members are lost.
The situation is the same if we look at lost members as a percentage of total members over the last 25 years, as apostle Cook suggests in the footnote to his statement: