I have data that looks like

YC      Age	Num
82	11	2
83	10	0
84	9	8
85	8	21
86	7	49
87	6	18
88	5	79
89	4	28
90	3	273
91	2	175

with a program 

mod1=lm(log(Num+1)~YC, data=box44) 
plot(log(Num+1)~YC, data=box44, pch=19, xlab="Year Class",
    ylab="Loge Number at age", ylim=c(0,6), xlim=c(91,82))
abline(lm(log(Num+1)~YC), col="blue", lwd=2)
summary(mod1)

I need to regress log(Num+1) against YC, but in descending (91 - 82) order so as to get a negative slope and positive intercept.  I can plot the values such that the regression line appears correct (the xlim statement), but I can't figure out how to force the regression from YC 91 through 82.  A call to the rev() function in front of YC does not produce the results I'm looking for.

More than likely, I'm overlooking something.  Thanks for any help you can provide.

SR

Steven H. Ranney
Graduate Research Assistant (Ph.D)
USGS Montana Cooperative Fishery Research Unit
Montana State University
PO Box 173460
Bozeman, MT 59717-3460

phone: (406) 994-6643
fax:   (406) 994-7479


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