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From |
jl591164@albany.edu |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: bivariate correlation analsis for longitudinal data |

Date |
Sun, 23 May 2010 14:07:27 -0400 (EDT) |

I try to do bivairate correlation analysis for longitudinal data. My understanding is to use the data in wide format and then do regular correlation of the x and y vairables, for example correlation of x at time 1 and y at time 2, x at time 2 and y at time 3, etc., or x and y both at the same time point. By doing so, do i assume that time effect is the name on the correlations at different time point? What is the appropriate way of conducting bivairate correlation analysis for longitudinal data? Eventually, i will fit randome intercept models for y on Xs. Thanks a lot. Junqing > Dear David > > I think that it might help if we were able to see a picture of the > graph that you have > in mind. Of course, sharing such a picture is not easy via Statalist, but > you could draw > something and share it using Jing, see > > http://www.michaelnormanmitchell.com/stow/capturing-and-sharing-screen-images.html > > I think that the growth model that you have in mind does not involve > any of the > interaction effects (note that age and age squared are not interacted with > anything) thus > when you look at the trajectory over time, the interactions you refer to > just get > "averaged out". I think it is possible that you might actually want more > than one graph, > for example you might like... > > 1) a graph with age on the X axis, the predicted outcome on the y axis, > and separate > lines for maternal IQ groups/treatment groups. This shows the growth curve > over time for > the six groups. Note that the growth curves will be parallel. > > 2) a graph with maternal IQ class on the X axis, separate lines for > treatment groups. > This will focus on the interaction. > > There may be multiple ways to touch the elephant, but I don't think > there is one way to > touch the elephant to get the entire picture. It is also possible that you > might be > interested in interacting age (and perhaps age squared) with some of your > other predictors > if you think that the growth trajectory depends on these factors. > > Finally, I would recommend "Applied Longitudinal Data Analysis: > Modeling Change and > Event Occurrence" by Judith D. Singer and John B. Willett to anyone who is > interested in > these kinds of models. It does not solve this exact problem, but is an > outstanding > reference, see > > http://www.ats.ucla.edu/stat/examples/alda.htm > > I hope this helps, > > Michael N. Mitchell > Data Management Using Stata - > http://www.stata.com/bookstore/dmus.html > A Visual Guide to Stata Graphics - > http://www.stata.com/bookstore/vgsg.html > Stata tidbit of the week - http://www.MichaelNormanMitchell.com > > > > On 2010-05-22 5.52 PM, David Torres wrote: >> Hello, >> >> I actually came upon the link Nick provided in a previous post >> (http://www.ats.ucla.edu/stat/stata/faq/mar_graph/margins_graph.htm) >> while I was working on this earlier today. The graph I was able to >> produce does seem useful in that it shows the difference in slope >> between child IQ scores of the different maternal IQ classes for both >> the control and treatment groups. I wonder, though, if I'm missing >> something by not showing growth. ??? >> >> Since the data include assessments at several time points (8 to be >> exact), should I not want a graph of the adjusted means at each time by >> maternal IQ and treatment group assignment? And shouldn't it be >> curvilinear given the quadratic? I guess I would like a growth curve >> that takes into account significant interaction effects. >> >> -------------------------------------------- >> >> David Diego Torres, MA(Sociology) >> PhD Candidate in Sociology >> >> >> * >> * For searches and help try: >> * http://www.stata.com/help.cgi?search >> * http://www.stata.com/support/statalist/faq >> * http://www.ats.ucla.edu/stat/stata/ > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: bivariate correlation analsis for longitudinal data***From:*Michael Mitchell <Michael.Norman.Mitchell@gmail.com>

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