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In R: ...
• 87.1k

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
1 vote

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

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

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

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 ...
• 57.2k

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: ...
• 57.2k

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

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: ...
• 57.2k
1 vote

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 ...
• 57.2k

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 ...
• 57.2k

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

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 ...
• 57.2k
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 ...
• 57.2k