The two-parameter gamma distribution, illustrated in Figs. 16.1 and 16.2, is [1, p. 85]
| (16.1) |  |
where
| ? | =shape parameter, |
| ? | =scale parameter, |
and
| ?( ?) | =gamma function evaluated at the value of ?. See Table 12.1 for this function's equation and its values. |
Specific characteristics of the gamma pdf are the following:
As may be seen from Figs. 16.1 and 16.2, the gamma distribution is skewed to the right. For ? < 1 as T ? 0 f( T) ? ?. For ? = 1, f( T = 0) = 
and f( T) decreases monotonically when T > 0 until at T ? ?, f( T) ? ?. For ? > 1 the distribution starts at zero for T = 0; increases, as T increases, to its mode; and decreases thereafter to zero as T ? ?. This behavior is similar to that of the Weibull pdf for various values of its ?. This flexibility makes it suitable for describing product life.
Figure 16.1: The gamma distribution with various values of ? and ? = 1.
Figure 16.2: The gamma distribution with various values of ? and ? = 3.
The effect of ? is identical to that of ? in the Weibull pdf. As ? is decreased the distribution gets...
TABLE OF CONTENTS 
