First, the good news: There are about a third fewer AIDS cases worldwide than has been estimated by the UN.

The latest estimates, due to be released publicly Tuesday, put the number of annual new HIV infections at 2.5 million, a cut of more than 40 percent from last year’s estimate, documents show. The worldwide total of people infected with HIV — estimated a year ago at nearly 40 million and rising — now will be reported as 33 million.

Now, the bad (though not unexpected) news: Politics drove the over-estimation of AIDS cases.

Having millions fewer people with a lethal contagious disease is good news. Some researchers, however, contend that persistent overestimates in the widely quoted U.N. reports have long skewed funding decisions and obscured potential lessons about how to slow the spread of HIV. Critics have also said that U.N. officials overstated the extent of the epidemic to help gather political and financial support for combating AIDS.

“There was a tendency toward alarmism, and that fit perhaps a certain fundraising agenda,” said Helen Epstein, author of “The Invisible Cure: Africa, the West, and the Fight Against AIDS.” “I hope these new numbers will help refocus the response in a more pragmatic way.”

The newer estimates are based on better methodologies, but the new report’s best feature may be the elimination of alarmist rhetoric.

The United Nations’ AIDS agency, known as UNAIDS and led by Belgian scientist Peter Piot since its founding in 1995, has been a major advocate for increasing spending to combat the epidemic. Over the past decade, global spending on AIDS has grown by a factor of 30, reaching as much as $10 billion a year.

But in its role in tracking the spread of the epidemic and recommending strategies to combat it, UNAIDS has drawn criticism in recent years from Epstein and others who have accused it of being politicized and not scientifically rigorous.

For years, UNAIDS reports have portrayed an epidemic that threatened to burst beyond its epicenter in southern Africa to generate widespread illness and death in other countries. In China alone, one report warned, there would be 10 million infections — up from 1 million in 2002 — by the end of the decade.

Piot often wrote personal prefaces to those reports warning of the dangers of inaction, saying in 2006 that “the pandemic and its toll are outstripping the worst predictions.”

But by then, several years’ worth of newer, more accurate studies already offered substantial evidence that the agency’s tools for measuring and predicting the course of the epidemic were flawed.

So the opinions of strategically placed advocates in the UN bureaucracy helped drive the worldwide politicization of AIDS policies, which resulted in widespread misperceptions of the science behind the estimates and distortions in funding for AIDS research across the board. And it took the UN years to figure all of this out.

What other science questions might the UN be giving similarly unwarranted alarmist treatment?