HALO (or diffusion) Effect

12-year-old children living in states where more than half of the communities have fluoridated water will have 26% fewer decayed tooth surfaces per year than 12-year-old children living in states where less than one-quarter of the communities are fluoridated.

12-year-old children living in states where more than half of the communities have fluoridated water will have 26% fewer decayed tooth surfaces per year than 12-year-old children living in states where less than one-quarter of the communities are fluoridated.