There are 12 Burr distributions.^{[}^{11}^{]} In many cases there are no published formulae for mean, variance, skewness or kurtosis. Although these might be developed, the majority of the distributions would offer a poor fit to process data that would almost certainly be bettered by other distributions for which the formulae exist. Indeed, they are largely neglected in the literature. The exception is Type XII, which we will show gives one of the best fits to the C_{4} in propane data.

The *Burr‐I distribution* is more commonly known as the uniform distribution, as described in Section 5.1.

The *Burr‐II distribution* is also known as the generalised logistic distribution, as described in the next chapter.

The *Burr‐III distribution* is described by the PDF

(21.1)

Figure 21.1 shows the effect of varying *δ*_{1} and *δ*_{2} with *α* fixed at 0 and *β* at 1. The CDF is

(21.2)

Fitting to the C_{4} in propane data gives *α* as −4.35, *β* as 3.84, *δ*_{1} as 4.86 and *δ*_{2} as 35.3. *RSS* is 0.0399.

The CDF can be inverted to give the QF.

(21.3)

The *Burr‐IV distribution* is described by the PDF

(21.4) ...

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