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Date:         Wed, 16 Jul 2003 14:04:50 -0400
Reply-To:     Mike Fay <rmf4@CDC.GOV>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Mike Fay <rmf4@CDC.GOV>
Subject:      Use SAS to fit this curve?

Hi folks,

I'm an amateur user of SAS, and even worse with statistics (laugh). Recently we charted some descriptive data that I'd like to fit to a curve, but am unsure how to ask SAS to do this. Or more especially, is there a way to ask SAS to search through the different fit possibilities and report on which are the best fit?

The data itself is appended. It shows the number of U.S. hazardous waste sites at which N or more chemicals are found in an exposure pathway. For example, the "n_chems = 2, n_sites = 588" observation means that two (or more) chemicals are found in an exposure pathway at 588 sites. (The universe N is 1706 -- many sites don't have a single exposure pathway.) (This data is draft and subject to revision as the generating algorithm is refined; do not cite or quote.)

If I play around with several possible fits, such as exponential or logarithmic, the best R2 is from an exponential fit. But it appears to be unable to cope with the steep drop-off and then levelling off, even though the curve seems pretty darn smooth to the eye. In other words, although I get an R2 of .955 in Excel's very simple "put a fit on this data" functionality, it obviously misses especially the beginning of the curve. And I don't know what else to do if Excel's missing it... but I'm willing to bet SAS (v9) can do a lot more than Excel ;)

Anyone is also welcome to point out any other math/stats software that might exist, particularly for the Windows environment. And the simpler (VERY simple) to operate, the better, lol.

TIA if you can help!

Mike, Atlanta

***

input N_Chems N_Sites;

cards;

1 743 2 588 3 475 4 390 5 321 6 266 7 214 8 185 9 161 10 136 11 111 12 102 13 87 14 74 15 69 16 61 17 56 18 52 19 47 20 46 21 44 22 39 23 36 24 33 25 29 26 26 28 24 29 22 30 20 31 19 32 18 37 16 38 15 39 13 40 11 41 10 42 9 48 7 49 6 51 5 56 4 58 3 62 2

;


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