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IAI Actuarial Core Principles · Risk Modelling and Survival Analysis · Introduction to copulas

If X has a continuous distribution function F_X, which statement is used to obtain the uniform inputs for a copula from observed losses?

For a continuous random variable X, applying its own distribution function gives F_X(X), which is uniformly distributed on (0,1). This probability integral transform produces the uniform margins needed by a copula, whatever the form of the original distribution.

  1. AF_X(X) has a uniform(0,1) distributionCorrect
  2. BF_X(X) has a standard normal distribution
  3. CF_X(X) has the same distribution as X
  4. DF_X(X) has an exponential distribution with mean 1
  5. F_X(X) has a uniform distribution only if X is normal

Explanation

The probability integral transform states that for continuous X, U=F_X(X) is uniform on (0,1). This is why a copula, with uniform marginals, captures dependence separately from the marginals. It holds for any continuous distribution, not only the normal.

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