FIGURE 12.4.1 Labeled shelf life. t, Labeled shelf life; x(t)'b, estimated mean degradation curve; 1, lower specification limit; ii(t), adjusted lower specification limit.
b, = where X, and Y, are as defined in (12.2.1). Under assumption A, the b, are independent and
b, ~ Np([3, + QQ (X'X,)-1). (12.4.16)
b, ~ Arp(it,ip). Hence, approximately,
x(t) (b, — b) (b, — b)' x(t).