The evaluation of geographic clusters must include consideration of potentially misleading aspects of ecologic studies.

The evidence from ecologic studies is not as strong as evidence from clinical trials or other types of research studies.

Although this result is consistent with a previous ecologic study [ 27 ] , suggesting that filtering at the level of a municipal system may not be successful in decreasing cases of cryptosporidiosis, this negative finding must be viewed with caution since our study was not specifically designed nor statistically powered to assess this exposure.

Demand for the devices grew so fast that in 2002 the leader of the group, Dr. Kris Pister of the University of California, Berkeley, helped found Dust Networks, of Hayward, Calif., which sells motes for many applications, including ecologic studies.

His debates in academic periodicals and published correspondence with R. William Field, Brian J. Smith (assistant professor of biostatistics, University of Iowa), Jerry Puskin (from the U.S. Environmental Protection Agency), Sarah Darby, and Sir Richard Doll and others regarding his radon-related ecologic studies are well known.

Evidence from ecologic and descriptive studies (e.g., international patterns studies, time series).

Sometimes ecologic studies can contribute to our understanding of combined effects.