So one of my ongoing reading projects is classic books about Mormonism. I recently finished sociologist Thomas F. O'Dea's 1950's tome 'The Mormons', which is perhaps best remembered for what it doesn't talk about, it's a "comprehensive" study of The Church of Jesus Christ of Latter-day Saints that doesn't mention the black priesthood or temple bans, or black people at all. It doesn't appear to have occurred to O'Dea as being a subject worth mentioning. 

Still the book was long the classic introduction to Mormonism by and for a non-Mormon audience. A collage level text but meant for a general and literate audience, it is at least in its early chapters, perhaps the best written and least boring introduction to the Church which I have encountered. There are three things in it I'd like to point out: 

1) The book mentions how Joseph Smith was sealed to the spouses of close associates, something I don't think the Church officially acknowledge unit the online essays in 2013 & 2014, O'Dea's 'The Mormons' was published in 1957. So much of Church history is just hidden in plane sight. 

2) O'Dea makes extensive use of another researchers study of Mormon activity rates from 1949, according to that study only around half of the church membership was active and participating mid Century.  Recent numbers I saw for the present day indicates its somewhere between 25% and 37% with the higher number being a very generous interpretation. Unlike most denominations the LDS give their membership numbers based on members on the rolls, not active participants so activity rates must be estimated by ward sizes, number of priesthood holders with callings, ect.  

3) In the section where O'Dea is speculating on the challenges the Church will face in the future he predicts that the biggest source of stress on the institution will be its more intellectually inclined members, spot one sixty years early.