Our GAAP loss ratio for the three months ended September 30, 2019 increased to 68.0% from 59.2% for the comparable 2018 period. Our GAAP loss ratio for the nine months ended September 30, 2019 increased to 65.1% from 63.0% for the comparable 2018 period. Our GAAP loss ratio excluding loss adjustment expenses for the three months ended September 30, 2019 was 59.5% compared to 51.4% for the comparable 2018 period. Our GAAP loss ratio excluding loss adjustment expenses for the nine months ended September 30, 2019 was 56.4% compared to 55.2% for the comparable 2018 period. Total prior year favorable development included in the pre-tax results for the three months ended September 30, 2019 was $3,204 compared to $13,048 for the comparable 2018 period. The decrease is mainly a result of the umbrella claim noted above. Total prior year favorable development included in the pre-tax results for the nine months ended September 30, 2019 was $25,541 compared to $39,348 for the comparable 2018 period.
Underwriting, Operating and Related Expenses. Underwriting, operating and related expenses for the three months ended September 30, 2019 decreased by $1,651, or 2.6%, to $60,845 from $62,496 for the comparable 2018 period. Underwriting, operating and related expenses for the nine months ended September 30, 2019 decreased by $2,738, or 1.5%, to $182,187 from $184,925 for the comparable 2018 period. Our GAAP expense ratio for the three months ended September 30, 2019 decreased to 30.7% from 31.7% for the comparable 2018 period. Our GAAP expense ratio for the nine months ended September 30, 2019 decreased to 30.9% from 31.7% for the comparable 2018 period.
Interest Expense. Interest expense was $22 for the three months ended September 30, 2019 and 2018. Interest expense was $67 for the nine months ended September 30, 2019 and 2018. The credit facility commitment fee included in interest expense was $56 for the nine months ended September 30, 2019 and 2018.
Income Tax Expense. Our effective tax rate was 19.7% and 21.2% for the three months ended September 30, 2019 and 2018, respectively. Our effective tax rate was 18.9% and 20.0% for the nine months ended September 30, 2019 and 2018. The effective tax rates for the three and nine months ended September 30, 2019 were lower than the statutory rate primarily due to the effects of tax-exempt investment income and the impact of stock-based compensation. The effective tax rates for the three and nine months ended September 30, 2018 were lower than the statutory rate primarily due to the effects of tax-exempt investment income.
Net Income. Net income for the three months ended September 30, 2019 was $15,619 compared to net income of $28,908 for the comparable 2018 period. Net income for the nine months ended September 30, 2019 was $71,499 compared to net income of $64,849 for the comparable 2018 period.
Non-GAAP Operating Income. Non-GAAP operating income as defined above was $15,079 for the three months ended September 30, 2019 compared to $27,115 for the comparable 2018 period. Non-GAAP operating income was $58,635 for the nine months ended September 30, 2019 compared to $65,662 for the comparable 2018 period.
Liquidity and Capital Resources
As a holding company, Safety’s assets consist primarily of the stock of our direct and indirect subsidiaries. Our principal source of funds to meet our obligations and pay dividends to shareholders, therefore, is dividends and other permitted payments from our subsidiaries, principally Safety Insurance. Safety is the borrower under our credit facility.
Safety Insurance’s sources of funds primarily include premiums received, investment income, and proceeds from sales and redemptions of investments. Safety Insurance’s principal uses of cash are the payment of claims, operating expenses and taxes, the purchase of investments, and the payment of dividends to Safety.
Net cash provided by operating activities was $69,651 and $90,397 during the nine months ended September 30, 2019 and 2018, respectively. Our operations typically generate positive cash flows from operations as most premiums are received in advance of the time when claim and benefit payments are required. Positive operating cash flows are expected to continue in the future to meet our liquidity requirements.