Posts Tagged ‘ Uncategorized ’

Correlation does not imply causation (parental involvement edition)

April 17, 2014
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The New York Times recently published an article on education titled "Parental Involvement Is Overrated". Most research in this area supports the opposite view, but the authors claim that "evidence from our research suggests otherwise".  Before you stop helping your children … Continue reading →

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Errors on percentage errors

April 16, 2014
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Errors on percentage errors

The MAPE (mean absolute percentage error) is a popular measure for forecast accuracy and is defined as     where denotes an observation and denotes its forecast, and the mean is taken over . Armstrong (1985, p.348) was the first (to my knowledge) to point out the asymmetry of the MAPE saying that “it has a bias favoring estimates that are below the actual values”. A few years later, Armstrong…

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On the determinant of the Hilbert matrix

April 16, 2014
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On the determinant of the Hilbert matrix

Last week I described the Hilbert matrix of size n, which is a famous square matrix in numerical linear algebra. It is famous partially because its inverse and its determinant have explicit formulas (that is, we know them exactly), but mainly because the matrix is ill-conditioned for moderate values of […]

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Generating tables in LaTeX

April 14, 2014
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Generating tables in LaTeX

Typing tables in LaTeX can get messy, but there are some good tools to simplify the process. One I discovered this week is tablesgenerator.com, a web-based tool for generating LaTeX tables. It also allows the table to saved in other formats including HTML and Markdown. The interface is simple, but it does most things. For complicated tables, some additional formatting may be necessary.     Similar functionality is available via…

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Summary of new features in SAS/IML 12.1

April 14, 2014
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Summary of new features in SAS/IML 12.1

I enjoy blogging about new functionality in the SAS/IML language because I can go into more depth and provide more complicated examples than the SAS/IML documentation. Today's article is a summary of all of my posts about features that were added to SAS/IML 12.1, which shipped in August 2012 as […]

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Shape File Selfies in ggplot2

April 12, 2014
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Shape File Selfies in ggplot2

In this post you will learn how to: Create your own quasi-shape file Plot your homemade quasi-shape file in ggplot2 Add an external svg/ps graphic to a plot Change a grid grob's color and alpha *Note get simple .md version … Continue reading →

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The #rOpenSci hackathon #ropenhack

April 10, 2014
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Editor's note: This is a guest post by Alyssa Frazee, a graduate student in the Biostatistics department at Johns Hopkins and a participant in the recent rOpenSci hackathon.  Last week, I took a break from my normal PhD student schedule … Continue reading →

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How to format decimals as fractions in SAS

April 10, 2014
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How to format decimals as fractions in SAS

Yesterday I blogged about the Hilbert matrix. The (i,j)th element of the Hilbert matrix has the value 1 / (i+j-1), which is the reciprocal of an integer. However, the printed Hilbert matrix did not look exactly like the formula because the elements print as finite-precision decimals. For example, the last […]

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The Hilbert matrix: A vectorized construction

April 9, 2014
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The Hilbert matrix: A vectorized construction

The Hilbert matrix is the most famous ill-conditioned matrix in numerical linear algebra. It is often used in matrix computations to illustrate problems that arise when you compute with ill-conditioned matrices. The Hilbert matrix is symmetric and positive definite, properties that are often associated with "nice" and "tame" matrices. The […]

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My forecasting book now on Amazon

April 9, 2014
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My forecasting book now on Amazon

For all those people asking me how to obtain a print version of my book “Forecasting: principles and practice” with George Athanasopoulos, you now can. Order on Amazon.com Order on Amazon.co.uk Order on Amazon.fr The online book will continue to b...

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