In the article “Randomized Stratified Sampling Methodology for Water Quality in Distribution Systems” (Journal of Water Resources Planning and Management, Vol. 130, Issue 4, pp. 330–338), V. Speight et al. proposed the method of stratified sampling to collect water samples for water-quality testing. The following table separates the Durham, North Carolina water distribution system into strata based on distance from the nearest treatment plant.

Distance from Stratum treatment center size Less than 1.5 miles 1310 1.5–less than 3.0 miles 3166 3.0–less than 4.5 miles 2825 4.5–less than 6.0 miles 1593 6.0–less than 7.5 miles 1350 7.5 miles or greater 1463 Use the table to design a procedure for obtaining a stratified sample (with proportional allocation) of 80 water samples from Durham.

Hint: Refer to the remarks about strata sample size on pages 44–45 following Example 1.14.

* AVONEX and MS.