Private U.S. property/casualty insurers' second-quarter net income rose to $10.18 billion after taxes, a 48% increase compared with a year earlier, according to an analysis released Thursday by Jersey City, N.J.-based Verisk Analytics Inc.'s Insurance Services Office Inc. unit and the Chicago-based Property Casualty Insurers Association of America.

Net written premiums for the second quarter grew 4.7% year to year to $120.06 billion.

The group's combined ratio improved to 100.8% from 104.8% a year earlier.

Net income for the first half of the year rose 42.4% over that of the same period in 2012 to $24.5 billion. Net written premiums grew 4.3% year to year to $237.25 billion, while the group's combined ratio improved to 97.9% from 101.9% during the same period a year earlier.

ISO and PCI noted in their analysis that insurers' results were driven by an $8.7 billion swing — with $2.3 billion in net income for the first half of this year vs. $6.4 billion in losses for the same period last year.

“The swing to net gains on underwriting in first-half 2013 reflects premium growth and a decline in loss and loss adjustment expenses,” ISO and PCI said in a statement.

Insurers' overall results for first-half 2013 also benefited from a $1.5 billion increase in net investment gains — the sum of net investment income and realized capital gains or losses on investments — to $27.1 billion in first-half 2013, the groups said.

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In addition, according to ISO's Property Claim Services unit, U.S. catastrophe losses in the first half of this year dropped 32.6% to $9.7 billion in direct insured losses before reinsurance recoveries. The data is for all insurers, including residual market insurers and foreign insurers and reinsurers. While catastrophe losses declined, they still were $500 million more than the $9.2 billion average for first-half direct catastrophe losses during the past 10 years.

For the second quarter, direct insured losses from catastrophes striking the United States excluding loss adjustment expenses totaled $7 billion, down $3.8 billion from the direct insured losses caused by catastrophes that struck the United States in second-quarter 2012, according to the PCS unit.

The figures are consolidated estimates for all private property/casualty insurers based on reports accounting for at least 96% of all business written by private U.S. property/casualty insurers.