2005-07-26_PWETC_AgendaPacket - Laserfiche WebLink

Home

March 23, 2005 Page 4 Table 3 City of Roseville Number of Samples Sorted Number of Number of Dual Total Average Single Stream Pounds Pounds per Stream Samples Sorted Sample Samples Before Pilot 22 4,708 214 During Pilot 26 7,105 273 8 Data Collection Total Pounds Sorted Average Pounds per Sample 2,269 284 Data sheets were completed during the sampling and sorting of the recyclable materials. The tare weight of the container, and the weight of the individual materials plus the tare weight, were recorded on the data sheets by the sort crew supervisor. The data sheets used in the study can be found in Attachment C. Statistical Modeling The data from the sorting events were entered into R. W. Beck's specially designed statistical model (Model). The Model has been developed in Microsoft Excel for easy accessibility and use. The Model statistically manipulates the data to calculate the mean, 90% confidence intervals, and standard deviation for individual material categories. In addition, the Model is structured to identify where specific samples could be considered statistical outliers. The mean represents the mathematical average or average percent of material composing the recyclable materials stream. The confidence interval is an expression of accuracy. It provides the upper and lower limits of the actual mean for all the recyclables in each sample, based on the sorting and sampling of the materials. For example, the 90% confidence interval represents that there is a 90% level of confidence that the true population mean falls within the upper and lower bounds of the confidence interval. The 90% confidence interval is the generally accepted standard by the industry for solid waste and recyclable materials composition studies. In general, the more samples that are sorted, the narrower the confidence interval. The narrower the intervals, the less variability in the data. We believe it is critical when comparing the recyclable materials composition results that the confidence intervals are considered along with the mean percentages. In addition, the total quantities of materials collected for each route were compiled during the sorting and sampling process. This data was analyzed separately to identify the mean quantities collected with the various collection methods and the applicable standard deviations. 01-00253-10 10 1-01 01 I 070001 I 13500 P:\13500 Ramsey Co. 2003\R T A \Roseville\F A\B 1544 * Final Data Analysis