On Wed, Jul 02, 2008 at 08:55:54PM -0500, Erik Iverson wrote: > Hello - > > Keld Jørn Simonsen wrote: > >Hi > > > >I have a problem with lm and predict > > > >I have > > > >us > > [1] 2789.53 3128.43 3255.03 3536.68 3933.18 4220.25 4462.83 4739.48 > > [9] 5103.75 5484.35 5803.08 5995.93 6337.75 6657.40 7072.23 7397.65 > >[17] 7816.83 8304.33 8746.98 9268.43 9816.98 10127.95 10469.60 > >10960.75 > >[25] 11685.93 12433.93 13194.70 13843.83 > > > > > > us.p > > [1] 227.62 229.92 232.13 234.25 236.31 238.42 240.59 242.75 244.97 247.29 > >[11] 250.05 253.39 256.78 260.15 263.33 266.46 269.58 272.82 276.02 279.20 > >[21] 282.31 285.25 288.10 290.85 293.53 296.26 299.08 301.97 > > > > us.l = lm(log(us) ~ log(us.p)) > >>predict(us.l,n.ahead=5) > > 1 2 3 4 5 6 7 8 > >8.079754 8.131908 8.181531 8.228692 8.274111 8.320224 8.367224 8.413588 > > 9 10 11 12 13 14 15 16 > >8.460813 8.509709 8.567285 8.636117 8.705057 8.772694 8.835719 8.897015 > > 17 18 19 20 21 22 23 24 > >8.957402 9.019376 9.079867 9.139289 9.196752 9.250495 9.302067 9.351347 > > 25 26 27 28 > >9.398927 9.446950 9.496094 9.545979 > > > > > >Why does predict not give me any predictions? The result of predict() is > >same lenght (28) as the us and us.p variables. > > The version of 'predict' being called on 'us.l' (i.e., predict.lm) is > doing predictions, and it should be giving you a result of identical > length as your original vectors. What are you expecting here? Your > usage of the 'n.ahead' parameter suggests to me you might be wanting to > fit your model using a different function than 'lm', and use its > corresponding prediction function.
Yes, what I have is actually some time series since 1980 on various countries - here USA production and population. I would like to estimate a model and then extrapolate for future years. Maybe predict.lm() is not the right function for that. What would be an adequate function then? best regards keld ______________________________________________ R-help@r-project.org mailing list 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.