Hospital Noise Levels Noise levels at various area urban hospitals were measured in decibels. The mean of the noise levels in 84 corridors was 61.2 decibels, and the standard deviation of the population was 7.9. Find the 95% confidence interval of the true mean. Source: M. Bayo, A. Garcia, and A. Garcia, "Noise Levels in an Urban Hospital and Workers’ Subjective Responses," Archives of Environmental Health 50, no. 3, p. 249 (May-June 1995). Reprinted with permission of the Helen Dwight Reid Educational Foundation. Published by Heldref Publications, 1319 Eiglitcuitli St N. W., Washington, D. C. 20036-1802. Copyright© 1995.