Blog Archives

Example 8.38: WriteXLS to create spreadsheets

May 16, 2011
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Example 8.38: WriteXLS to create spreadsheets

In our last entry, we described reading Excel files. In this entry, we do the opposite: write native Excel files.RIn R, the WriteXLS package provides this functionality. It uses perl to do the heavy lifting, and the main complication is to install th...

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To attach() or not attach(): that is the question

May 3, 2011
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To attach() or not attach(): that is the question

R objects that reside in other R objects can require a lot of typing to access. For example, to refer to a variable x in a dataframe df, one could type df$x. This is no problem when the dataframe and variable names are short, but can become burdensom...

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Example 8.36: Quadratic equation with real roots

April 29, 2011
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Example 8.36: Quadratic equation with real roots

We often simulate data in SAS or R to confirm analytical results. For example, consider the following problem from the excellent text by Rice:Let U1, U2, and U3 be independent random variables uniform on . What is the probability that the roots...

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Example 8.34: lack of robustness of t test with small n

April 12, 2011
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Example 8.34: lack of robustness of t test with small n

Tim Hesterberg has effectively argued for a larger role for resampling based inference in introductory statistics courses (and statistical practice more generally). While the Central Limit Theorem is a glorious result, and the Student t-test remarkabl...

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Example 8.28: should we buy snowstorm insurance?

February 28, 2011
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Example 8.28: should we buy snowstorm insurance?

It's been a long winter so far in New England, with many a snow storm. In this entry, we consider a simulation to complement the analytic solution for a probability problem concerning snow. Consider a company that buys a policy to insure its revenue ...

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Example 8.27: using regular expressions to read data with variable number of words in a field

February 25, 2011
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Example 8.27: using regular expressions to read data with variable number of words in a field

A more or less anonymous reader commented on our last post, where we were reading data from a file with a varying number of fields. The format of the file was:1 Las Vegas, NV --- 53.3 --- --- 12 Sacramento, CA --- 42.3 --- --- 2The complication in the...

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Example 8.26: reading data with variable number of words in a field

February 22, 2011
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Example 8.26: reading data with variable number of words in a field

A student came with a question about how to snag data from a PDF report for analysis. Once she'd copied things her text file looked like:1 Las Vegas, NV --- 53.3 --- --- 12 Sacramento, CA --- 42.3 --- --- 23 Miami, FL --- 41.8 --- --- 34 Tucson, AZ --...

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Example 8.25: more latent class models (plus a graphical display)

February 15, 2011
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Example 8.25: more latent class models (plus a graphical display)

In recent entries (here, here, here and here), we've been fitting a series of latent class models using SAS and R. One of the most commonly used and powerful package for latent class model estimation is Mplus. In this entry, we demonstrate how to use...

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Example 8.24: MplusAutomation and Mplus

February 7, 2011
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Example 8.24: MplusAutomation and Mplus

In recent entries (here, here, and here), we've been fitting a series of latent class models using SAS and R. One of the most commonly used and powerful software package for latent class model estimation is Mplus. This commercial software includes su...

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Example 8.23: Expanding latent class model results

January 31, 2011
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Example 8.23: Expanding latent class model results

In Example 8.21 we described how to fit a latent class model to data from the HELP dataset using SAS and R (using poLCA(), and then followed up in example 8.22 using randomLCA(). In both entries, we classified subjects based on their observed (manifes...

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