Dr. Warren Winkelstein, a physician and researcher whose groundbreaking studies connected unprotected sex between men to AIDS, smoking to cervical cancer and air pollution to chronic lung disease, died July 22 at his home in Point Richmond, Calif. He was 90.

The cause was complications from an infection, according to the University of California, Berkeley, where he was an emeritus professor of epidemiology and a former dean at the School of Public Health.

Epidemiologists look for patterns of illness in populations, and Winkelstein was considered a master at designing rigorous studies to answer tough questions about the causes, risk factors and transmission of disease.

He was best known for an AIDS project, the San Francisco Men’s Health Study, which began in 1984 and tracked 1,034 single men, some straight and some gay, from parts of the city with the highest rates of AIDS.

At that time, the virus that causes AIDS had been identified, but scientists did not know what practices, sexual or otherwise, might increase the risk of infection. A number of research projects were set up to find out.

What set Winkelstein’s study apart was his insistence on using a technique called probability sampling to find participants. It involved selecting blocks from census tracts and actually knocking on doors to ask men to participate, rather than putting advertisements in newspapers and waiting for responses. The goal was to ensure that the study included a representative sample of men so that the findings could be broadly applied.

The study lasted 12 years and led to about 150 articles in scientific journals. It confirmed, with solid data, what researchers had suspected: men who had the most male partners and were the receptive partner during unprotected anal sex had the highest risk of infection. The study also yielded important information about the incubation period of AIDS.

“It was a uniquely important study because it showed both how common HIV infection was among men who have sex with men and the central role of unsafe sexual behavior in transmission of the virus causing AIDS,” said Dr. Arthur Reingold, the dean for research at Berkeley’s School of Public Health. It was the only study at the time, he said, that used a representative sample of men living in San Francisco.

Reingold said that, paradoxically, Winkelstein’s insistence on sound methodology nearly cost him the government money needed to keep the project going. Other researchers were conducting similar studies but using different techniques to recruit participants. The differences meant that Winkelstein’s data could not be combined with that from the other groups. The agency providing money wanted to cut him off but eventually conceded that his work was too valuable.

The same disciplined approach led Winkelstein to findings that were so counterintuitive that other researchers refused to believe them. He suggested in 1977 that smoking was a risk factor for cervical cancer, and 25 years later it was widely accepted that smoking does increase the odds of cervical cancer in women who are also exposed to a common sexually transmitted virus.

In the 1960s, in Buffalo, Winkelstein designed a study showing that air pollution could cause chronic lung disease and that lung disease in polluted areas was not just caused by risk factors related to poverty. The findings helped shape national air quality standards.

Warren Winkelstein was born on July 1, 1922, in Syracuse, N.Y. His father was a prominent lawyer.

From an early age, he was surrounded by people who were concerned about social issues. The family lived near Syracuse University, and his mother would often arrange dinner parties for scholars who went to lecture there. A close friend of the family was a department chairman at the medical school who had a strong interest in public health.

“So I think my background led me in a direction of social concern,” Winkelstein said in an interview in the journal Epidemiology in 2004.

He kept teaching after he retired in 1991 and also wrote biographical sketches of leading figures in the history of epidemiology. He always urged his students to work with other scientists.

“You can make a lot of mistakes individually,” he told Epidemiology. “But by collaboration, you eliminate a lot of dumb errors.”