Month SVL volume
4 57 48.131
4 57.75 43.854
4 59.05 41.005
4 56.75 50.697
4 57.44 41.729
4 56.41 43.593
4 60.35 29.609
4 56.28 59.218
4 57.68 42.439
4 58.82 36.616
5 55.67 40.301
5 61.81 25.661
5 57.01 38.136
5 57.99 37.472
5 58.29 35.794
5 59.72 32.076
5 58.62 34.215
5 59.07 34.899
5 57.04 39.478
5 58.11 36.294
5 59.94 31.691
5 53.74 49.052
5 54.65 42.729
5 60.34 28.628
5 60.07 31.649
5 55.85 39.478
6 57.9 15.545
6 57.3 17.321
6 63.32 14.002
6 58.5 15.377
6 55.1 17.502
6 56.15 18.423
6 60.06 14.804
6 61.28 14.377
7 59.04 25.296
7 57.98 27.003
7 55.79 27.316
7 52.71 29.675
7 60.96 22.703
7 59.49 23.687
7 53.77 28.306
7 61.44 22.029
以上的数据存在一个名为data2.txt下。
data2<-read.table(file="D:/R workplace/data2.txt",sep=" ",header=TRUE)

plot(data2[,2],data2[,3])
abline(lm(formula=volume~SVL,data=data2))

sum(data2[,1]==4)
sum(data2[,1]==5)
sum(data2[,1]==6)
sum(data2[,1]==7)

plot(data2[1:10,2],data2[1:10,3])
abline(lm(formula=volume~SVL,data=data2[1:10,]))

plot(data2[11:26,2],data2[11:26,3])
abline(lm(formula=volume~SVL,data=data2[11:26,]))

plot(data2[27:34,2],data2[27:34,3])
abline(lm(formula=volume~SVL,data=data2[27:34,]))

plot(data2[35:42,2],data2[35:42,3])
abline(lm(formula=volume~SVL,data=data2[35:42,]))

用以上的代码可以看出，按月做线性回归的话，还是比整体好。

你可以分月去做。 具体的信息，你用
summary(lm(formula=volume~SVL,data=data2[35:42,]))去看。