How should I build my model?

I get this question a lot, and it’s difficult to answer at first glance–it depends too much on your particular situation.

There are really three parts to the approach to building a model: the strategy, the technique to implement that strategy, and the decision criteria used within the technique. [click to continue…]

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Why Use Stata?

Like many people with graduate degrees, I have used a number of statistical software packages over the years. Through work and school I have used Eviews, SAS, SPSS, R and Stata. Some were more difficult to use than others but if you used them often enough you would become proficient to take on the task at hand (though some packages required greater usage of George Carlin’s 7 dirty words). There was always one caveat which determined which package I used…

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Examples for Writing up Results of Mixed Models

If you have worked on or know of a paper that used mixed models, please give us the reference in the comments. Links to online versions are great too, if you have one.

Trust me, many people in your field are looking for an example and will be happy to cite it.

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When Does Repeated Measures ANOVA not work for Repeated Measures Data?

Repeated measures ANOVA is the approach most of us learned in stats classes, and it works very well in certain designs. But it’s a bit limited in what it can do. Sometimes trying to fit a data set into a repeated measures ANOVA requires too much data gymnastics—averaging across repetitions or pretending a continuous predictor isn’t really.

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R Is Not So Hard! A Tutorial, Part 18: Re-Coding Values

You can re-code an entire vector or array at once. To illustrate, let’s set up a vector that has missing values.

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R Is Not So Hard! A Tutorial, Part 17: Testing for Existence of Particular Values

Sometimes you need to know if your data set contains elements that meet some criterion or a particular set of criteria. For example, you may need to know if you have missing data (NAs) lurking somewhere in a large data set…

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R Is Not So Hard! A Tutorial, Part 16: Counting Values within Cases

SPSS has the Count Values within Cases option, but R does not have an equivalent function. Here are two functions that you might find helpful, each of which counts values within cases inside a rectangular array…

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R Is Not So Hard! A Tutorial, Part 15: Counting Elements in a Data Set

Combining the length() and which() commands gives a handy method of counting elements that meet particular criteria…

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Random Sample from a Uniform Distribution in R Commander

Why We Needed a Random Sample of 6 numbers between 1 and 10000 As you may have read in one of our recent newsletters, this month The Analysis Factor hit two milestones: 10,000 subscribers to our mailing list 6 years in business. We’re quite happy about both, and seriously grateful to all members of our […]

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Spotlight Analysis for Interpreting Interactions

Not too long ago, a client asked for help with using Spotlight Analysis to interpret an interaction in a regression model.

Spotlight Analysis? I had never heard of it.

As it turns out, it’s a (snazzy) new name for an old way of interpreting an interaction between a continuous and a categorical grouping variable in a regression model…

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