Catriona: You have already been roundly (and appropriately) chastised for your sins. So I need not join the chorus.
Instead, let me just briefly focus on the substance of what you are trying to do, because I continue to believe it's wrong. Here's the leading question: Could you just as logically reversed your x and y allometric variables and done things as: lm(Contrast_log_MTL_ALL ~ Contrast_log_FTL_ALL) ## ignoring the offset business and expected the slope to be 1 for this, too. If the answer to this question is yes, then your whole approach is wrong and you need to consult a local statistician or post on a statistical list, as I suggested earlier. If the answer is no, it can only be done the way you showed us, then you're fine. Cheers, Bert On Sat, Nov 24, 2012 at 6:05 PM, Catriona Hendry <hen...@gwmail.gwu.edu>wrote: > Hi, > > @ Albyn, David.. No, its not homework. Its basic groundwork for testing > allometric relationships for a graduate project I am working on. I read the > guide before posting, I spent half the day trying to understand how I am > going wrong based on the advice given to others. > > @Bert, David... I apologise for the lack of code, I wasn't sure how to > explain my problem and I guess I went about it the wrong way. > > I do think this is what I need to be doing, I am testing allometric > relationships of body size against a predicted isometric (1:1) > relationship. So I would like to know if the relationship between my > variables deviates from that. > > Hopefully the information below will be what is needed. > > Here is the part of the code relevant to the regression and plot: > > > >plot(Contrast_log_MTL_ALL, Contrast_log_FTL_ALL) > > >Regression_PhyloContrasts_ALL <- lm(Contrast_log_FTL_ALL ~ > Contrast_log_MTL_ALL, offset=1*Contrast_log_MTL_ALL) > abline(Regression_PhyloContrasts_ALL) > > the plot that resulted is attached as an image file. > > > Below are the vectors of my variables. The are converted from other values > imported and indexed from a csv file, so unfortunately I don't have matrix > set up for them. > > Contrast_log_FTL_ALL Contrast_Log_MTL_ALL 83 0.226593 0.284521 84 > 0.165517 0.084462 85 -0.1902 -0.0055 86 0.585176 0.639916 87 -0.01078 > 0.118011 88 0.161142 0.073762 89 -0.08566 -0.04788 90 -0.13818 -0.0524 > 91 -0.02504 -0.21099 92 -0.05027 -0.07594 93 -0.11399 -0.07251 94 > -0.07299 -0.08247 95 -0.09507 -0.04817 96 0.207591 0.151695 97 -0.14224 > -0.05097 98 0.06375 -0.0229 99 0.04607 0.06246 100 0.257389 0.190531 > 101 -0.0612 -0.10902 102 -0.1981 -0.24698 103 -0.12328 -0.36942 104 > 0.269877 0.341989 105 0.125377 0.227183 106 0.087038 -0.05962 107 > 0.114929 0.096112 108 0.252807 0.305583 109 -0.0895 -0.08586 110 > -0.38483 -0.20671 111 -0.72506 -0.63785 112 -0.37212 -0.21458 113 > 0.010348 0.117577 114 -0.09625 -0.0059 115 -0.26291 -0.25986 116 > 0.056922 0.064041 117 0.051472 -0.09747 118 -0.05691 0.075005 119 > 0.117095 -0.15497 120 -0.01329 -0.12473 121 0.098725 0.020522 122 > -0.0019 -0.01998 123 -0.12446 -0.02312 124 0.019234 0.031391 125 > 0.385366 0.391766 126 0.495518 0.468946 127 -0.09251 -0.08045 128 > 0.147965 0.139117 129 -0.03143 -0.02319 130 -0.19801 -0.14924 131 > 0.014104 -0.01917 132 0.031872 -0.01381 133 -0.01412 -0.04381 134 > -0.12864 -0.08527 135 -0.07179 -0.03525 136 0.31003 0.29553 137 > -0.09347 -0.11903 138 -0.10706 -0.16654 139 0.078655 0.065509 140 > 0.08279 -0.00766 141 0.181885 0.001414 142 0.345818 0.496323 143 > 0.235044 0.095073 144 -0.03022 0.039918 145 0.042577 0.136586 146 > 0.064208 0.001379 147 -0.02237 -0.03009 148 -3.55E-05 0.040197 149 > 0.011168 0.087116 150 0.019964 0.071822 151 -0.04602 -0.06616 152 > 0.083087 0.038592 153 0.032078 0.107237 154 -0.21108 -0.22347 155 > 0.122959 0.297917 156 -0.05898 0.012547 157 -0.07584 -0.21588 158 > -0.00929 -0.06864 159 -0.01211 -0.04559 160 0.090948 0.136582 161 > 0.016974 0.018259 162 -0.04083 0.016245 163 -0.20328 -0.31678 > > > > > > > On Sat, Nov 24, 2012 at 8:22 PM, Bert Gunter <gunter.ber...@gene.com>wrote: > >> 1. The model is correct : lm( y~ x + offset(x)) >> ( AFAICS) >> >> 2. Read the posting guide, please: Code? I do not know what you mean by: >> >> " this resulted in a regression line that was plotted perpendicular to >> the data when added with the abline function." >> >> Of course, maybe someone else will groc this. >> >> 3. I wonder if you really want to do what you are doing, anyway. For >> example, in comparing two assays to see whether they give "similar" >> results, you would **not** do what you are doing. If you care to follow up >> on this, I suggest you post complete context to a statistical mailing list, >> not here, like stats.stackexchange .com. Also, feel free to ignore me, of >> course. I'm just guessing. >> >> Cheers, >> Bert >> >> Cheers, >> Bert >> >> >> On Sat, Nov 24, 2012 at 4:27 PM, Catriona Hendry >> <hen...@gwmail.gwu.edu>wrote: >> >>> Hi! >>> >>> I have a question that is probably very basic, but I cannot figure out >>> how >>> to do it. I simply need to compare the significance of a regression slope >>> against a slope of 1, instead of the default of zero. >>> >>> I know this topic has been posted before, and I have tried to use the >>> advice given to others to fix my problem. I tried the offset command >>> based >>> on one of these advice threads as follows: >>> >>> Regression <- lm(y~x+offset(1*x)) >>> >>> but this resulted in a regression line that was plotted perpendicular to >>> the data when added with the abline function. >>> >>> I would be extremely grateful for your help!! >>> >>> Thanks!! >>> >>> Cat >>> >>> [[alternative HTML version deleted]] >>> >>> ______________________________________________ >>> 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. >>> >> >> >> >> -- >> >> Bert Gunter >> Genentech Nonclinical Biostatistics >> >> Internal Contact Info: >> Phone: 467-7374 >> Website: >> >> http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm >> >> >> > > > -- > ----------------------------------------- > *Catriona Hendry* > *Postgraduate Student* > *Biological Sciences Department* > *George Washington University* > *hen...@gwmail.gwu.edu* > > -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm [[alternative HTML version deleted]] ______________________________________________ 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.
