I think you want CI's for intercepts, not "means" (what is a "mean" for a line??). If so, the ?confint function will give this to you for the lot effect estimates when applied to a model fitted without an intercept:
myfit <-lm(y~ lot-1+time) confint(myfit) Further discussion should be directed to a statistical site or a local statistician, as these are not R issues. Cheers, Bert Bert Gunter Genentech Nonclinical Biostatistics (650) 467-7374 "Data is not information. Information is not knowledge. And knowledge is certainly not wisdom." Clifford Stoll On Tue, May 5, 2015 at 9:53 AM, li li <hannah....@gmail.com> wrote: > Hi all, > I have the following data in which there is one factor lot with six > levels and one continuous convariate time. > I want to fit an Ancova model with common slope and different intercept. So > the six lots will have seperate paralell > regression lines.I wanted to find the upper 95% confidence limit for the > mean of the each of > the regression lines. It doesnot seem straightforward to achieve this using > predict function. Can anyone give some suggestions? > > Here is my data. I only show the first 3 lots. Also I show the model I > used in the end. Thanks very much! > Hanna > > y lot time > [1,] 4.5 1 0 > [2,] 4.5 1 3 > [3,] 4.7 1 6 > [4,] 6.7 1 9 > [5,] 6.0 1 12 > [6,] 4.4 1 15 > [7,] 4.1 1 18 > [8,] 5.3 1 24 > [9,] 4.0 2 0 > [10,] 4.2 2 3 > [11,] 4.1 2 6 > [12,] 6.4 2 9 > [13,] 5.5 2 12 > [14,] 3.5 2 15 > [15,] 4.6 2 18 > [16,] 4.1 2 24 > [17,] 4.6 3 0 > [18,] 5.0 3 3 > [19,] 6.2 3 6 > [20,] 5.9 3 9 > [21,] 3.9 3 12 > [22,] 5.3 3 15 > [23,] 6.9 3 18 > [24,] 5.7 3 24 > > >> mod <- lm(y ~ lot+time) >> summary(mod) > Call: > lm(formula = y ~ lot + time) > Residuals: > Min 1Q Median 3Q Max > -1.5666 -0.3344 -0.1343 0.4479 1.8985 > Coefficients: > Estimate Std. Error t value Pr(>|t|) > (Intercept) 4.74373 0.36617 12.955 2.84e-14 *** > lot2 -0.47500 0.41129 -1.155 0.2567 > lot3 0.41250 0.41129 1.003 0.3234 > lot4 0.96109 0.47943 2.005 0.0535 . > lot5 0.98109 0.47943 2.046 0.0490 * > lot6 -0.09891 0.47943 -0.206 0.8379 > time 0.02586 0.02046 1.264 0.2153 > --- > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
