Does an Age Explain Membership Growth in the U.S.

Median Age by State: 2012

The United States like much of the  world is experiencing declining birth rates and its inevitable consequence, an aging population.  In “Does an Aging World Explain Lower Convert Baptisms?,” I find a statistically significant relationship between the median age in seventy five countries and the growth in net membership of The Church of Jesus Christ of Latter-day Saints.  Older countries grow more slowly than younger countries.  I find that the same relationship exists in the United States; membership grows more slowly in old states than young states. 

Median age and the birth rate of a state measure age.  Data came from the U.S. Census population estimates for 2012. I consider two models, one using the median age and the other replacing median age with the birth rate.  The variable, the number of missions in a state, adjusts for the size of Church and the intensity of missionary effort.  All variables in both models are statistically significant and the birth rate acts as a nearly identical substitute variable for median age.  The higher the median age, the lower the increase in net membership and the higher the birth rate, the lower the increase in net membership.   

The model specification is weak in two ways.  First, growth is tied to the existing population but my simple model specification does not capture this aspect of population growth.  Second, the data should be expanded to include more than one time period.  My results have limitations but they are suggestive that the growth of the Church is slowed by an aging population.  I offer two possible explanations.  People are more likely to change beliefs when pushed by events such as the formation of a family, the birth of children and financial stress.  These events are more likely to occur early in life rather than late.  Finally, falling fertility is driving the increase in median age.  A generation or two ago, the growth of the Church was greater because LDS families were bigger.  The conversion of a young family was likely to add three or four children to the Church rather than today’s 2.1.