New answers tagged sas
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3
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Why would SAS proc mixed produce residual variance estimates under AR1 covariance structure, but none for unstructured covariance?
The AR(1) covariance matrix is:
$$
\begin{bmatrix}
\sigma^2 & \rho\sigma^2 & \rho^2\sigma^2 & \rho^3\sigma^2 \\
\rho\sigma^2 & \sigma^2 & \rho\sigma^2 & \rho^2\sigma^2 \...
- 57.2k
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Identifying groups with better response to treatment
It is not clear how you found that:
Overall, the treatment was effective
Assuming that you fitted a simple regression model in SAS:
...
- 57.2k
3
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Could lower limit of a confidence interval be negative?
Yes ! The lower confidence bound can be negative. This is reflected by the p-values being quite large, around 0.5. This means that if the true value for the parameter is actually zero, then the ...
- 57.2k
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How can I verify the linear hypothesis in a multiple logistic regression using SAS?
Sure, one way to do this is to introduce nonlinear terms into the model, and test their significance. A good way to do this is with regression splines. First, you need to create spline variables for ...
- 57.2k
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How is the SAS REPLICATE statement in PROC NLMIXED different from a FREQ statement?
TL;DR:
The key distinction lies in their level of operation (subject-level vs observation-level) and how they contribute to the likelihood estimation. Understanding this difference is crucial in model ...
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6
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Generalized estimating equation and data format
PROC GENMOD requires data in long format. Data can be reshaped from wide to long format with PROC TRANSPOSE:
For example:
...
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5
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SAS fails to fit a mixed model
The SAS model you have fitted is not the same as the one you fitted with lme4::lmer. You have specified an unstructured variance-covariance matrix for the residual ...
- 57.2k
4
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SAS Proc Mixed Repeated VS Random (or Both)?
The main difference between these models is that you are treating timepoint as categorical in the first model:
...
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2-way Anova on Unequal Group Proportions
Which method or technique should I use to account for the binary response variable?
For a binary response you can use logistic regression. In SAS that would be ...
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4
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Test for synergy using Bliss independance model for two drugs
This could be quite a long answer as it's something I've also been working on recently. The Bliss Independence model (Bliss, 1939; Greco et al., 1995, Geary, 2013) is an Effect-Based method (in ...
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In SAS, does the using the GLM statement ABSORB invalidate the standard errors of the parameter estimates?
In SAS, if you ABSORB a variable in PROC GLM, it adjusts its effects but does not include it in the VCV matrix of the estimated ...
- 57.2k
7
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Doubts about mixed model (R vs SAS) with nested random effects
Can I ignore this warning ?
You certainly can, but I doubt that would be a good idea.
The problem you have encountered seems to be due to the way the variables are coded. If we look at a cross ...
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6
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Accepted
How should I analyse this experiment with two blocking factors
Is this another type of Randomized Complete Block Design?
It is very closely related but this seems to be a Latin Square design, not a RCB design, though we could say that it's an extension of the ...
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6
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Accepted
What is a Randomized Complete Block Design. How do we create one and analyze it?
There are a number of different designs that use the term "Randomised Complete Block Design", but they are all based on a very basic idea, that of blocking. A block is just another factor (a ...
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