# Posts Tagged ‘ R-english ’

## MAT8886 the Dirichlet distribution

February 15, 2012
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In the course, still introducing some concept of dependent distributions, we will talk about the Dirichlet distribution (which is a distribution over the simplex of ). Let denote the Gamma distribution with density (on ) Let denote independent...

## MAT8886 elliptically contoured distributions

February 15, 2012
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(This article was first published on Freakonometrics - Tag - R-english, and kindly contributed to R-bloggers) Last week, we’ve introduced the concept of exchangeable variables, i.e. satisfying for any matrix  , i.e. is a permutation matrix: belongs to the orthogonal group, , and with elements in . It is possible to extend that family, considering all matrices in the...

## MAT8886 exchangeability, credit risk and risk measures

February 10, 2012
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Exchangeability is an extremely concept, since (most of the time) analytical expressions can be derived. But it can also be used to observe some unexpected behaviors, that we will discuss later on with a more general setting. For instance, in a old...

## MAT8886 a short word on profile likelihood

February 7, 2012
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Profile likelihood is an interesting theory to visualize and compute confidence interval for estimators (see e.g. Venzon & Moolgavkar (1988)). As we will use is, we will plot But more generally, it is possible to consider where . Then (...

## On linear models with no constant and R2

February 2, 2012
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In econometrics course we always say to our students that "if you fit a linear model with no constant, then you might have trouble. For instance, you might have a negative R-squared". So I tried to find databases on the internet such that, when we ...

## MAT886 mean excess function (and reinsurance)

February 1, 2012
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Tomorrow, in the course on extreme value, we will focus on applications. We will discuss reinsurance pricing. Consider a random variable , a threshold and define the mean excess function. This function is known in life insurance as the average ...

## It is "simply" the average value

January 24, 2012
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for some obscure reasons, simple things are usually supposed to be simple. Recently, on the internet, I saw a lot of posts on the "average time in which you hold a stock", and two rather different values are mentioned "Take any stock in the United ...

## Even odds

January 22, 2012
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This evening, I found a nice probabilistic puzzle on http://www.futilitycloset.com/ "A bag contains 16 billiard balls, some white and some black. You draw two balls at the same time. It is equally likely that the two will be the same color as diff...

## MAT8886 Extremes and sums (of i.i.d. random variables)

January 20, 2012
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Yesterday, we have discussed briefly sums and maximas of i.i.d. random variables using the concept of subexponential distributions. Today, we will introduce the concept of regular variation: a positive function is said to be regularly varying (at i...

## Gold price and fear

January 18, 2012
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Via @theEconomist, I understood that there might be connections between the price of Gold (which is said to be extremely high nowadays) and the VIX SP500 index (the option volatility index, i.e. the so-called "fear index", as discussed - in French-...