Gauging the savings in future malpractice costs - the key goal of a reform bill rushed through a special legislative session - is a virtually impossible task, experts say.

MedChi, the state medical society, and the Maryland Hospital Association are scheduled to present their assessment of the legislation at a press conference today.

Gov. Robert L. Ehrlich Jr. has promised that an outside actuary hired by the state will follow with its assessment of the bill, which he has vowed to veto.

But experts warn that aside from a steep cut in malpractice insurance premiums scheduled to take effect this year, a lack of data and varying circumstances make it much more difficult to evaluate provisions designed to rein in future costs through changes in the legal system, insurance regulation and patient safety requirements.

State lawmakers are counting on the long-term reforms to eventually reduce the number of malpractice cases that are filed as well as the amounts paid in settlements and court awards.

In the process they hope to moderate the rising insurance premiums doctors say are threatening their practices.

"It's hard to predict how any particular intervention is likely to stabilize premiums," said William M. Sage, a physician who is also professor of law at Columbia University and who is conducting a study of malpractice reforms.

For example, no one knows precisely how many wrongful death judgments there were in Maryland last year that would have been subject to the lower monetary cap set by the bill.

And there are no precedents on which to base projections of the impact of other provisions, such as an enhanced system to collect data on medical errors.

Cheye Calvo, a policy analyst for the National Conference of State Legislatures in Washington, said lawmakers in different states often ask how much savings in malpractice costs can be generated by particular reforms, but that impact can vary from state to state.

"You're dealing with a unique set of circumstances," he said. "You can't just plug in a new number. It's impossible to predict with any degree of confidence how it will affect future costs."

Part of the difficulty stems from limitations in the data, such as in cases of deaths that resulted from malpractice, Calvo and Sage said.

While the bill would cut in half the maximum that could be paid in non-economic damages from malpractice, Maryland, like most other states, has no public source of data on how much money is paid out annually.

Medical Mutual Insurance Society of Maryland, the doctor-owned insurer that covers most of the state's physicians, has made public data on verdicts and settlements. But that data doesn't distinguish between death cases and others, or show how much of each payout was for non-economic damages that would be subject to the cap.

The state Health Claims Arbitration Office flags death cases, but collects data only on filings, and not on whether they ultimately resulted in a court judgment or settlement or no payment at all.

Payouts in all malpractice cases are reported to the board that assesses discipline against doctors, but its information isn't public. And most payouts result from settlements rather than court verdicts, and settlements generally include confidentiality agreements.

Some states collect more data than others, Calvo said. For example, in Missouri "you're able to look and say, 'had the cap been in existence, these verdicts would have been reduced.'" The bill would expand claims data collection in Maryland.

Sage said there's no complete data comparing premiums in different states - data that could give an indication of how certain types of reforms affect the rates doctors pay. "I've never actually seen statistics about premiums I believe," he said.

Ehrlich has repeated promises to veto the bill because it extends a 2 percent premium tax to health management organizations and because he believes reforms in the legal system don't go far enough. He officially received the bill yesterday, giving him until next Monday to sign it or to follow through on his veto threat.