Page 266 - Solid Waste Analysis and Minimization a Systems Approach

244 SOLID WASTE CHARACTERIZATION BY BUSINESS ACTIVITIES

15.3 SIC Code Grouping Validation

The initial grouping of business to characterize solid waste generation was based on
SIC codes. U.S. environmental regulators typically use SIC codes to report waste gen-
eration data of business sectors. The literature review indicated the use of SIC codes
for this purpose has not been statistically validated. This section discusses the valida-
tion procedure and results to justify this usage.
The following statistical validation procedure was used. Two analyses were con-
ducted, first to examine the variability within SIC code groups and second to examine
the variability between SIC code groups:

1 Develop 95 percent confidence intervals on the mean composition percentage for
each material in each of the 65 SIC code groups.
2 Conduct one-way ANOVA (analysis of variance) on each waste material across all
waste groups at the 95 percent confidence level.
3 Validate the consolidation of businesses by SIC codes to investigate:
a Similar variation exists within wastes groups (verify each material’s confidence
interval is equal to or less than plus or minus 5 percentage points)
b Significant variation exists between waste groups (verify the ANOVA results are
statistically different for each waste material)

Ninety-five percent confidence intervals were developed for each waste material in
each of the 65 SIC code groups using the following equation:

±
xt s
α/ 2
n

where x = the average waste material composition percentage for the random sample
t
α / 2 = the t-value with v = n − 1 degrees of freedom
s = the sample standard deviation
n = the sample size

All solid waste materials were within the desired 5 percent confidence interval to
validate the grouping of SIC codes. The minimum range was 0.5 percent and the max-
imum range was 4.6 percent. Table 15.1 displays an example of the results for organic
wastes in SIC code group 01: agriculture production crops.
The 95 percent confidence interval range of 2.4 percent indicates that 95 percent of
the mean percentages of organic waste for SIC code group 01 (agriculture production
crops) will be between 19.6 percent and 24.4 percent. The 95 percent confidence inter-
val 2.4 percent is well within the desired range of 5 percent to validate grouping mate-
rial composition percentages based on SIC codes.
One-way ANOVA was applied to examine difference between all 65 SIC code
groups and materials. Table 15.2 is the one-way ANOVA for organic waste. As
shown in the table, the test statistic (F = 1354.734) is significantly higher than