Three bar charts show the distribution of coupons at three points in time: December 2011, December 2015, and December 2022. December 2011 chart shows 81% of the bonds were 5s and 4% were 6s; the remainder were mostly 4s. Compared with December 2011, the December 2015 chart shows that more bonds were 3s and 4s, and fewer bonds were 5s and 6s. The December 2022 chart shows an even bigger shift of the distribution to 2s, 3s, and 4s, and away from 5s and 6s.