# Posts Tagged ‘ stats ’

## Covariance structures

October 26, 2011
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$Covariance structures$

In most mixed linear model packages (e.g. asreml, lme4, nlme, etc) one needs to specify only the model equation (the bit that looks like y ~ factors...) when fitting simple models. We explicitly say nothing about the covariances that complete … Continue reading →

## Queueing up in R, continued

October 20, 2011
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Shown above is a queueing simulation. Each diamond represents a person. The vertical line up is the queue; at the bottom are 5 slots where the people are attended. The size of each diamond is proportional to the log of the time it will take them to be attended. Color is used to tell one

## Maximum likelihood

October 13, 2011
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$Maximum likelihood$

This post is one of those ‘explain to myself how things work’ documents, which are not necessarily completely correct but are close enough to facilitate understanding. Background Let’s assume that we are working with a fairly simple linear model, where … Continue reading →

## Waiting in line, waiting on R

October 13, 2011
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I should state right away that I know almost nothing about queuing theory. That’s one of the reasons I wanted to do some queuing simulations. Another reason: when I’m waiting in line at the bank, I tend to do mental calculations for how long it should take me to get served. I look at the

## Simulating data following a given covariance structure

October 12, 2011
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Every year there is at least a couple of occasions when I have to simulate multivariate data that follow a given covariance matrix. For example, let’s say that we want to create an example of the effect of collinearity when … Continue reading →

## On R versus SAS

October 6, 2011
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A short while ago there was a discussion on linkedin about the use of SAS versus R for the enterprise. I have thought a bit about the issue but, as I do not use Linkedin, I did not make any … Continue reading →

## Linear regression with correlated data

October 5, 2011
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I started following the debate on differential minimum wage for youth (15-19 year old) and adults in New Zealand. Eric Crampton has written a nice series of blog posts, making the data from Statistics New Zealand available. I will use … Continue reading →

## How many NYC restaurants get As on their health inspections?

August 15, 2011
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Decision Science News is no stranger to misleading infographics in free New York newspapers. We could stop reading them entirely, but we find that playing "spot the infographic flaw" makes time fly on the subway. Recently we saw the above graphic in a paper called Metro. Can you spot the goof?

## The Stats Clinic

July 27, 2011
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Here at HSL we have a lot of smart kinda-numerate people who have access to a lot of data. On a bad day, kinda-numerate includes myself, but in general I’m talking about scientists who have have done an introductory stats course, but not much else. When all you have is a t-test, suddenly everything looks