by Christos Giannoulis, PhD

Attributes are often measured using multiple variables with different upper and lower limits. For example, we may have five measures of political orientation, each with a different range of values.

Each variable is measured in a different way. The measures have a different number of categories and the low and high scores on each measure are different.

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December 2018 Member Webinar: Those Darn Ratios!

Ratios are everywhere in statistics—coefficient of variation, hazard ratio, odds ratio, the list goes on. Join Elaine Eisenbeisz as she presents an overview of the how and why of various ratios we use often in statistical practice.

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Statistical Models for Truncated and Censored Data

Can we ignore the fact that a variable is bounded and just run our analysis as if the data wasn’t bounded?

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Your Questions Answered from the Interpreting Regression Coefficients Webinar

Q16: The different reference group definitions (between R and SPSS) seem to give different significance values. Is that because they are testing different hypotheses? (e.g. “Is group 1 different from the reference group?”)

A: Yes. Because they’re using different reference groups, we have different hypothesis tests and therefore different p-values.

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November 2018 Member Webinar: Meta-analysis

Meta-analysis is the quantitative pooling of data from multiple studies. Meta-analysis done well has many strengths, including statistical power, precision in effect size estimates, and providing a summary of individual studies. But not all meta-analyses are done well.

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Should I Specify a Model Predictor as Categorical or Continuous?

Predictor variables in statistical models can be treated as either continuous or categorical.

Usually, this is a very straightforward decision about which way to specify each predictor.

Categorical predictors, like treatment group, marital status, or highest educational degree should be specified as categorical.

Likewise, continuous predictors, like age, systolic blood pressure, or percentage of ground cover should be specified as continuous.

But there are numerical predictors that aren’t continuous. And these can sometimes make sense to treat as continuous or sometimes make sense as categorical.

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Count vs. Continuous Variables: Differences Under the Hood

One of the most important concepts in data analysis is that the analysis needs to be appropriate for the scale of measurement of the variable. The focus of these decisions about scale tends to focus on levels of measurement: nominal, ordinal, interval, ratio.

These levels of measurement tell you about the amount of information in the variable. But there are other ways of distinguishing the scales that are also important and often overlooked.

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Differences in Model Building Between Explanatory and Predictive Models

Suppose you are asked to create a model that will predict who will drop out of a program your organization offers. You decide you will use a binary logistic regression because your outcome has two values: “0” for not dropping out and “1” for dropping out.

Most of us were trained in building models for the purpose of understanding and explaining the relationships between an outcome and a set of predictors. But model building works differently for purely predictive models. Where do we go from here?

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October 2018 Member Webinar: Latent Growth Curve Models

What statistical model would you use for longitudinal data to analyze between-subject differences with within-subject change?

Most analysts would respond, “a mixed model,” but have you ever heard of latent growth curves? How about latent trajectories, latent curves, growth curves, or time paths, which are other names for the same approach?

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The Difference Between Link Functions and Data Transformations

Generalized linear models—and generalized linear mixed models—are called generalized linear because they connect a model’s outcome to its predictors in a linear way. The function used to make this connection is called a link function. Link functions sounds like an exotic term, but they’re actually much simpler than they sound.

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