Year Ended December 31, 2019 Compared with Year Ended December 31, 2018 Year Ended December 31, 2018 Compared with Year Ended December 31, 2017 Premium income increased compared to 2017 due primarily to growth in the in-force block driven by higher persistency and rate increases in our group long-term disability product line. Net investment income decreased compared to 2017 due primarily to a lower yield on our fixed-rate bonds, partially offset by a higher level of invested assets and higher investment income from inflation index-linked bonds. The increase in net investment income attributable to these index- linked bonds was offset by an increase in the reserves for future claim payments related to inflation index-linked group long-term disability and group life policies. Benefits experience was consistent with 2017 as favorable claims recoveries in our group long-term disability product line were offset by unfavorable claims activity in our group life and supplemental product lines and the impact of inflation-linked increases in benefits. Commissions and the deferral of acquisition costs decreased relative to 2017 due to lower sales. The amortization of acquisition costs was lower in 2018 compared to 2017 due to a decline in the deferred asset. The other expense ratio was lower relative to 2017 due to higher premiums and our continued focus on expense management and operating efficiencies. Commissions and the deferral of acquisition costs were higher relative to 2018 due to higher sales. The amortization of acquisition costs was lower in 2019 compared to 2018 due to a decline in the level of the deferred asset. The other expense ratio was lower relative to 2018 due to higher premiums and our continued focus on expense management. Benefits experience was unfavorable relative to 2018 due to unfavorable mortality experience and a reduction in the claim reserve discount rate to recognize the impact on future portfolio yields from the higher than normal level of bond calls experienced during 2019, partially offset by lower inflation-linked increases in benefits related to our group products. Net investment income was higher compared to 2018 due to higher miscellaneous investment income resulting from a higher than normal level of bond calls, and a higher level of invested assets, partially offset by a lower yield on fixed-rate bonds and lower investment income from inflation index-linked bonds, which we invest in to support the claim reserves associated with certain of our group policies that provide for inflation-linked increases in benefits. The decrease in net investment income attributable to these index-linked bonds was offset by a decrease in the reserves for future claim payments related to the inflation index-linked group long-term disability and group life policies. Premium income was higher compared to 2018 due to higher overall persistency, sales growth, and the impact of rate increases in the group long- term disability product line. 68