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The Department of Environmental Quality (DEQ) for the State of Oregon has compiled data on the amount of solid waste generated, recovered and disposed for each of the 34 counties in Oregon (plus the Portland metropolitan area or Metro). Counties and Metro are referred to as "wastesheds" by the DEQ, a term analagous to watershed in hydrology; a wasteshed collects solid waste into a concentrated waste stream. Solid waste monitored by the DEQ includes both household waste (garbage, recyclables, etc.) and some industrial waste such as construction debris, but apparently does not include industrial wastes from manufacturing, agricultural processing, petrochemical plants, etc.

Data are given on the population and tons of solid waste disposed in 35 wastesheds in Oregon in 1998. Disposal takes place by both landfilling and incineration. Though not stated, operators of these two types of disposal facilities presumably monitor the disposed tonnage and report these values to the DEQ.

The amount of solid waste disposed each year depends upon the amount generated or produced and the amount recycled or recovered. The production rate is probably strongly correlated with population, whereas the recycling rate depends upon a large number of factors, including the proportion of recyclables in the waste stream, ease of recycling, education programs, etc.

Population size is most likely the dominant variable in waste disposal, and the graph supports this assumption, showing a strong positive correlation between population and solid waste disposed in 1998. The relationship between people and waste disposed is linear, with a very high correlation coefficient. The slope of the regression line gives a typical "disposal rate" of a bit less than 1 ton of solid waste per citizen per year. Note that the Y-intercept is not zero; what is the significance, if any, of a non-zero intercept?

The datum for the Portland metropolitan area has been excluded from the graph, to better view the majority of data points. Is the Metro datum an "outlier"? Students could run regressions both excluding and including this datum; how different are these regressions?

Reference: Oregon State Department of Environmental Quality, Solid Waste Program. Data available at: http://www.deq.state.or.us/wmc/solwaste/data/percapdisposal1998.html

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 Solid Waste Disposed in 1998 by Wasteshed State of Oregon Wasteshed Population Disposed Per capita (people) (tons) (tons/person) Baker 16,700 12,376 0.741 Benton 71,860 45,551 0.634 Clatsop 34,700 30,716 0.885 Columbia 42,300 23,004 0.544 Coos 61,400 37,434 0.610 Crook 16,650 14,232 0.855 Curry 22,000 12,264 0.557 Deschutes 104,900 101,313 0.966 Douglas 100,300 86,369 0.861 Gilliam 2,100 1,320 0.629 Grant 8,000 3,174 0.397 Harney 7,600 1,794 0.236 Hood River 19,500 14,931 0.766 Jackson 172,800 136,337 0.789 Jefferson 8,709 8,709 1.000 Josephine 73,000 40,518 0.555 Klamath 62,000 62,603 1.010 Lake 7,400 6,361 0.860 Lane 313,000 261,958 0.837 Lincoln 43,200 41,127 0.952 Linn 107,090 75,807 0.708 Malheur 29,200 20,052 0.687 Marion 271,750 237,166 0.873 Metro 1,363,100 1,196,486 0.878 Milton-Freewater 6,500 5,586 0.859 Morrow 9,400 5,893 0.627 Polk 58,940 36,790 0.624 Sherman 1,900 1,092 0.575 Tillamook 24,000 15,063 0.628 Umatilla 60,600 52,484 0.866 Union 24,400 15,610 0.640 Wallowa 7,200 4,526 0.629 Wasco 22,600 17,997 0.796 Wheeler 1,600 359 0.224 Yamhill 82,460 68,901 0.836 Total 3,258,859 2,695,903 0.827

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