California Department of Resources Recycling and Recovery (CalRecycle) 

Local Government Central

Why is There a Diversion Rate Calculation Range (Maximum and Minimum)?

Note: This page contains historical data from CIWMB's (now known as CalRecycle) statewide goal measurement prior to 2007 that estimated a diversion percentage. For 2007 and subsequent years, CalRecycle compares reported disposal tons to population to calculate per capita disposal expressed in pounds/person/day. This new goal measurement system is described in the Goal Measurement: 2007 and Later web page.

The Board's approved method to estimate a diversion rate uses eight input values to adjust a base-year waste generation amount forward to a report-year waste generation amount. This includes base-year and report-year values for:

  • Population
  • Employment
  • Taxable Sales
  • Consumer Price Index (CPI)

Taxable Sales input values are dollar amounts of retail transactions reported to the State Board of Equalization (BOE) by over one million retailers. Population, employment, and the CPI are estimates, and in most cases very good estimates.[1] However, careful measurements almost always vary. The environment of every measurement is slightly different. One combination of selected population, employment, taxable sales, and inflation (CPI) measurements results in a "maximized" diversion rate estimate. Another combination of these measurements results in a "minimized" diversion rate estimate.

For each of these input values, jurisdictions have choices. First, a jurisdiction may use a standard ("default") value provided by CIWMB, or it may propose an alternative input value from a scientifically reliable third-party source.[2] Second, the input value may be measured at jurisdiction or countywide level. An exception is CPI because this estimate is available only by metropolitan area or statewide.

For annual reports to the Board, each jurisdiction should select population, employment, taxable sales, and CPI input values that most accurately reflect base-year to report-year percentage change in waste generation within their jurisdiction.

A jurisdiction may use one factor (for base year and report year) measured at the jurisdiction level, and another factor (for base year and report year) measured at the countywide level. For example, jurisdiction population may be used with countywide employment, jurisdiction taxable sales, and statewide CPI.

If a jurisdiction decides to use only "default" population, employment, taxable sales, and inflation (CPI) values, it usually has eight possible combinations of these input values (2 x 1 x 2 x 2 = 8):

  • Population (Jurisdiction or Countywide)
  • Employment[3] (Countywide)
  • Taxable Sales (Jurisdiction or Countywide)
  • Consumer Price Index (Metropolitan Area or Statewide)

For example, the "City of Almond Creek" has eight possible combinations of "default" population, employment, taxable sales, and CPI values for 1998:

Population Employment Taxable Sales Consumer Price Index Estimated Diversion Rate
Jurisdiction Countywide Countywide Metropolitan area 55% (minimized)
Jurisdiction Countywide Countywide Statewide 55%
Countywide Countywide Countywide Metropolitan area 56%
Countywide Countywide Countywide Statewide 56%
Jurisdiction Countywide Jurisdiction Metropolitan area 60%
Jurisdiction Countywide Jurisdiction Statewide 61%
Countywide Countywide Jurisdiction Metropolitan area 61%
Countywide Countywide Jurisdiction Statewide 61% (maximized)

As illustrated above, the range of diversion rate estimates is usually narrow. The highest diversion rate estimate is "maximized," and the lowest diversion rate estimate is "minimized."


[1] For 1998 through 2000, taxable sales values published by CIWMB were estimated using 1st through 3rd quarter Board of Equalization data, and a 4th quarter CIWMB estimate using prior year 3rd to 4th quarter percent change.

[2] Title 14, California Code of Regulations, Division 7, Chapter 9. Section 18797.2 Adjustment Factor Sources.

[3] Relevant jurisdiction-level employment data is readily available only for each 10-year population census: 1990, 2000, 2010, etc.

Last updated: December 3, 2010
Local Government Central 
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