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EXAMPLE #2:
Different chemicals were added to the reporting requirement in different years.
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Some chemicals have been required since reporting began in 1990. Additional chemicals were required starting in each of the years 1991, 1992, and 1993. This means that total quantities reported by a company may have risen from 1990 through 1993 simply because more chemicals were being reported, not because more chemicals were being used. Reporting progress for chemicals for which reporting was first required in different years is best done by reporting progress only over those years when the chemicals were all reported.
Suppose, for example, that a company used three chemicals, A, B and C. The quantities reported might look something like this:
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1990
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1991
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1992
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1993
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1994
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1995
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1996
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1997
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Chem A
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50,000
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60,000
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70,000
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80,000
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70,000
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50,000
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60,000
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70,000
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Chem B
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0
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100,000
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110,000
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110,000
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100,000
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120,000
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130,000
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130,000
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Chem C
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0
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0
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200,000
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210,000
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200,000
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220,000
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190,000
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190,000
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At first glance, it would seem that the total chemical use for the company might be:
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1990
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1991
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1992
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1993
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1994
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1995
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1996
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1997
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Total
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50,000
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160,000
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380,000
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400,000
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370,000
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390,000
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380,000
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390,000
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It looks like the chemical use for the company more than doubled from 50,000 in 1990 to 160,000 in 1991 and then more than doubled again to 380,000 in 1992. However, of the three chemicals, only Chemical A was required to be reported in 1990. Chemical B wasn't required to be reported until 1991 and Chemical C was first required to be reported in 1992. So, adding up the numbers tells you how much was reported but does not show how much was actually used since the company was probably using both chemicals B and C in 1990.
Given these changing reporting requirements, one way to look at the trend is to report the quantities for all chemicals that were required to report in common years. For this example, it is possible to say that the total chemical use for this company increased from 380,000 in 1992 to 390,000 in 1997. In this case, a report of use for the company might look like this:
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1990
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1991
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1992
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1993
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1994
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1995
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1996
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1997
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Total
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N/A **
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N/A **
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380,000
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400,000
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370,000
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390,000
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380,000
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390,000
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** A change in reporting requirements makes it impossible to report total use for these years on a basis consistent with the other years reported.
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