From the article:
The placebo-controlled, double-blinded trial examined the effect of testosterone therapy on sexual function in a group of 470 men. The men were enrolled in the study through 12 academic medical centers. The participants were at least 65 years old and had low testosterone levels, based on the average results of multiple tests. All of the men had a heterosexual partner.
[…]
The men treated with testosterone therapy displayed consistent improvement in libido and in 10 of the 12 sexual activity measurements, including frequency of intercourse, masturbation and nighttime erections. In comparison, men who received the placebo did not change their questionnaire responses significantly over the course of the year-long study.