The increases in direct written premiums and net written premiums are a result of new business production and rate increases. For the year ended December 31, 2024, the Company achieved policy count growth across all lines of business, including 10.0%, 4.5% and 8.7% in Private Passenger Automobile, Commercial Automobile and Homeowners lines, respectively, compared to the same period in 2023. Additionally, for the year ended December 31, 2024, average written premium per policy increased 14.1%, 10.7% and 8.9% in Private Passenger Automobile, Commercial Automobile and Homeowners lines, respectively, compared to the same period in 2023.
Net earned premiums for the quarter ended December 31, 2024 increased by $43.1 million, or 19.0%, to $269.1 million from $226.0 million for the comparable 2023 period. Net earned premiums for the year ended December 31, 2024 increased by $176.3 million, or 21.1%, to $1,010.7 million from $834.4 million for the comparable 2023 period.
For the quarter ended December 31, 2024, losses and loss adjustment expenses incurred increased by $20.9 million, or 12.1%, to $193.0 million from $172.1 million for the comparable 2023 period. For the year ended December 31, 2024, losses and loss adjustment expenses incurred increased by $74.3 million, or 11.6%, to $716.6 million from $642.3 million for the comparable 2023 period. The increase in losses is driven by our larger policy counts and current market conditions, specifically inflationary impacts on our Private Passenger Automobile book of business.
Loss, expense, and combined ratios calculated for the quarter ended December 31, 2024, were 71.7%, 30.2%, and 101.9%, respectively, compared to 76.1%, 30.4%, and 106.5%, respectively, for the comparable 2023 period. The decrease in loss and expense ratios is driven by the increase in earned premiums. The loss ratio is also favorably impacted by the moderation of loss severity in the Private Passenger Automobile line. Loss, expense, and combined ratios calculated for the year ended December 31, 2024 were 70.9%, 30.2%, and 101.1%, respectively, compared to 77.0%, 30.7%, and 107.7%, respectively, for the comparable 2023 period. The prior year loss ratio was impacted by severe weather events totaling $41.2 million of losses.
Total prior year favorable development included in the pre-tax results for the quarter ended December 31, 2024 was $13.0 million compared to $12.4 million for the comparable 2023 period. Total prior year favorable development included pre-tax results for the year ended December 31, 2024 was $51.9 million compared to $47.4 million for the comparable 2023 period. Included within 2024 current and prior year development is $10.1 million related to the Massachusetts Property Insurance Underwriting Association (“FAIR Plan”). On April 1, 2024, the Massachusetts Division of Insurance approved a restructuring of the FAIR Plan that resulted in the Company recognizing current and prior year development.
Net investment income for the quarter ended December 31, 2024 decreased by $0.1 million, or 0.7% to $14.8 million from $14.9 million for the comparable 2023 period. Net investment income for the year ended December 31, 2024 decreased by $0.7 million, or 1.2%, to $55.7 million from $56.4 million for the comparable 2023 period. The decrease is due to the earned interest from our higher yield bonds and variable rate secured and senior bank loans. Net effective annualized yield on the investment portfolio was 4.0% for the quarter ended December 31, 2024 compared to 4.2% for comparable 2023 period. Net effective annualized yield on the investment portfolio was 3.9% for the year ended December 31, 2024 compared to 4.0% at 2023. The investment portfolio’s duration on fixed maturities was 3.5 years at December 31, 2024 compared to 3.6 years at December 31, 2023.
Non-GAAP Measures
Management has included certain non-GAAP financial measures in presenting the Company’s results. Management believes that these non-GAAP measures are useful to 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.