three months ended March 31, 2024, average written premium per policy increased 13.5%, 6.4%, and 7.4% in Private Passenger Automobile, Commercial Automobile and Homeowners lines, respectively, compared to the same period in 2023.
For the quarter ended March 31, 2024, loss and loss adjustment expenses incurred increased by $1.2 million, or 0.7%, to $168.4 million from $167.2 million for the comparable 2023 period. The slight increase is driven by larger policy counts offset by improved results in our homeowners lines.
Loss, expense, and combined ratios for the quarter ended March 31, 2024 were 71.3%, 30.6%, and 101.9%, respectively, compared to 87.2%, 31.3%, and 118.5%, respectively, for the comparable 2023 period. Total prior year favorable development included in the pre-tax results for the quarter ended March 31, 2024 was $11.0 million compared to $11.5 million for the comparable 2023 period. The prior year loss ratio was impacted by a severe weather event, totaling $32.1 million of losses for the quarter ended March 31, 2023.
Net investment income for the quarter ended March 31, 2024 increased by $1.5 million, or 11.5%, to $15.2 million from $13.7 million for the comparable 2023 period. The increase is a result of increases in interest rates on our fixed maturity portfolio compared to the prior year. Net effective annualized yield on the portfolio was 4.3% for the three months ended March 31, 2024 compared to 3.8% for the comparable 2023 period. Our duration on fixed maturities was 3.5 years at March 31, 2024 and 3.6 years at December 31, 2023, respectively.
Non-GAAP Measures
Management has included certain non-GAAP financial measures in presenting the Company’s results. Management believes that these non-GAAP measures better explain the Company’s results of operations and allow for a more complete understanding of the underlying trends in the Company’s business. These measures should not be viewed as a substitute for those determined in accordance with generally accepted accounting principles (“GAAP”). In addition, our definitions of these items may not be comparable to the definitions used by other companies.
Non-GAAP operating income and non-GAAP operating loss per diluted share consist of our GAAP net income adjusted by the net realized gains on investments, change in net unrealized gains on equity securities, credit loss expense and taxes related thereto. For the quarter ended March 31, 2024, an increase of $7.7 million for the change in unrealized gains on equity investments was recognized within loss before income taxes, compared to an increase of $0.8 million for the change in unrealized gains on equity investments in the comparable 2023 period. Net income and earnings per diluted share are the GAAP financial measures that are most directly comparable to non-GAAP operating income and non-GAAP operating income per diluted share, respectively. A reconciliation of the GAAP financial measures to these non-GAAP measures is included in the financial highlights below.
About Safety: Safety Insurance Group, Inc., based in Boston, MA, is the parent of Safety Insurance Company, Safety Indemnity Insurance Company, Safety Property and Casualty Insurance Company, Safety Northeast Insurance Company, and Safety Northeast Insurance Agency, Inc. Operating exclusively in Massachusetts, New Hampshire, and Maine, Safety is a leading writer of property and casualty insurance products, including private passenger automobile, commercial automobile, homeowners, dwelling fire, umbrella and business owner policies.
Additional Information: Press releases, announcements, U. S. Securities and Exchange Commission (“SEC”) Filings and investor information are available under “About Safety,” “Investor Information” on our Company website located at www.SafetyInsurance.com. Safety filed its December 31, 2023 Form 10-K with the SEC on February 28, 2024 and urges shareholders to refer to this document for more complete information concerning Safety’s financial results.