When is a Multilevel Model not appropriate?

Chris Daman
Chris Daman|April 24, 2013

I recently received this interesting question regarding Multilevel Models after one of my last blog posts: Question: Can you tell me when a multilevel-model is not appropriate? I have data that by design is clustered but the random intercept in the null model is not significant. I have seen advice [...]

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Multilevel Models Part 2: What is a Multilevel Model?

Chris Daman
Chris Daman|March 28, 2013

Multilevel models (also called hierarchical linear models) are used to analyze clustered or grouped data, as well as longitudinal or repeated measures data. Consider the simple scenario shown below, where Y is continuous and is shown as a function of a continuous predictor variable, X (which has been standardized). If [...]

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Multilevel Models Part 1: Do I Need a Multilevel Model?

Chris Daman
Chris Daman|March 27, 2013

If you have data where the observations are not independent due to nesting or clustering, you may need a multilevel model. Another scenario that would require a multilevel model is if you have data where observations have been gathered multiple times on the same subject (a.k.a., longitudinal data or repeated [...]

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ESTIMATE Statements - the final installment

Chris Daman
Chris Daman|May 2, 2012

FINALLY…the simplest ESTIMATE statements to write are for continuous variables not involved in interactions or higher order terms. Consider a data set containing the 2004 SAT scores for each of the 50 states. The file includes the combined math and verbal SAT scores (TOTAL), the state (STATE) and the percent [...]

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"Easy button" for ESTIMATE statements

Chris Daman
Chris Daman|April 25, 2012

My previous blog demonstrated the most difficult type of ESTIMATE statement to write—a two-way (or higher) ANOVA with interactions. An “easy button” for ESTIMATE statement comes by having a simpler model. Models with only main effects and no interactions make writing ESTIMATE statements straightforward.  Consider first a one-way ANOVA. A [...]

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The magical ESTIMATE (and CONTRAST) statements

Chris Daman
Chris Daman|April 23, 2012

When asked to select the best (or worst) of something in a business setting, do you wish you had “magic glasses” to see the answer? PROC GLM and other statistical modeling procedures have their own versions of such an item with their ESTIMATE (and CONTRAST) statements. They allow you to [...]

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The Human Side of Statistical Process Control: Three Applications of SAS/QC You Might Not Have Thought About

Catherine Truxillo
Catherine Truxillo|March 22, 2011

When you think of statistical process control, or SPC for short, what industry first comes to your mind? In the past 10 or 15 years, diverse industries have begun to standardize processes and administrative tasks with statistical process control. While the top two bars of the industrial Pareto chart are [...]

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Who Ate My Lunch? Discriminant Thresholds to Reduce False Accusations

Catherine Truxillo
Catherine Truxillo|February 18, 2011

Lunch. For some workers, it’s the sweetest part of an otherwise bitter day at the grindstone. Nothing can turn that sweetness sour like going into the breakroom to discover that someone has taken your lunch and eaten it themselves. Nothing like that ever happens here at SAS. But if it [...]

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The Punchline: MANOVA or a Mixed Model?

Catherine Truxillo
Catherine Truxillo|February 2, 2011

Edited to add: Thanks for Larry Madger for noticing an important omission in my code below. I have updated the programs to include the response variables, which enables the responses to have different means. So, if you were reading last week, we talked about how to structure your data for [...]

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The Bayes theorem, explained to an above-average squirrel

Michele Reister
Michele Reister|January 31, 2011

Editor’s Note: The following question was recently asked of our statistical training instructors. Terry Woodfield, along with Bob Lucas took the time to write this eloquent and easily digestible answer. Question: I’m trying to get a general – very general – understanding what the Bayes theorem is, and is used [...]

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