do not attend BYU or another high-LDS concentration university like USU, SVU, SUU or UVU have about a 90% probability of being inactive by age 25. They get a local job, marry a local non-LDS girl/boy friend and drop away from the church. Attending 4 years of institute increase the odds a little bit.
This is from a white paper by Clayton Christiansen distributed to Stake Presidents about 7-8 years ago and is supported by my observations in stakes in South Carolina, Connecticut and Michigan. Our stake in Connecticut had around 600 YSAs. About 50-60 of those who did not leave home for school were active.