JAGGI AND FREEDMAN
For measurement of pH pollutant, a range between 6 and 8.5 was considered normal (McDuffie and Haney, 1973) and pH outside this range is considered pollution. Equation (3) is used to determine acidity-cdkalinity pollution for each pipe, and equation (4) is used for determination of acidity-alkalinity pollution for the firm.
Phij T,{Ph Max -8.5) + — X) (6 - Z'/iMin^vt) (3) P k. P k. Ph,i.F,t + Ph.2.F,2 + + Phjj.Fj^ Phi = ^—^ (4)
where F^, Fj2, . . . Fjj) = water flow for plant j, firm i. After the measures for each pollutant are calculated, a weighted pollution index is developed for each pollutant. The BOD and TSS raw scores (see column 1 of Table 1) are converted into per ton production scores (see column 2 of Table 1) for making comparative analysis across all firms. The use of BOD and TSS per ton of production provides a relative measure of pollution performance and size and efficiency are taken into account. This is also consistent with the EPA's policy of basing their mill pollution standards on mill size along with other factors. Furthermore, the studies by Spicer (1978), Ingram and Frazier (1980) and Freedman and Jaggi (1988) all utilized pollution performance adjusted for some measure of size. The firms with the highest per ton of production score of an individual pollutant is assigned the pollution index of 100. The indices for other firms are calculated in relation to the highest index. For example, the TSS measure of 23.71 per ton of production for International Paper is the highest, this firm is assigned the index of 100. Boise Cascade with a TSS measure of 10.25 of production is given the index of 43.2. This procedure is followed for TSS as well as BOD to calculate a pollution index for each firm (see column 3 of Table 1). The scores based on per ton of production are not considered appropriate for the pH measure since the formula to calculate pH pollution averages the mill sizes based on water flow. Therefore, pH raw scores are used for the calculation of the pH index. The pollution indices for each pollutant are combined to arrive at an overall pollution index. In view of the difficulty of determining the relative detriment of the three pollutants to the environment, each pollutant is weighted equally.
Economic and Market Performance Indicators
Because the impact of pollution performance will be felt both on profitability as well as on productivity, the following five economic performance indicators have been selected for the study: Net Income, Return on Equity, Return of Assets, Cash Flow/Equity, and Cash Flow/Assets. The measure of Net Income is selected because this measure is commonly used for evaluating the economic performance of firms. But net income alone does not sufficiently reflect economic