Twenty items undergo a nonreplacement test, which is terminated
at 100 hours. Failure times observed were 10, 16, 17, 25, 31, 46, and 65
hours. Calculate (1) the one-sided approximate 90% confidence interval (a = 0.10), and (2) the
two-sided approximate 90% confidence limits of q,
the mean life.

That is, 114.83 hours is
the lower (two-sided) 90% confidence limit for q, the true mean life, and
459.67 hours is the upper (two-sided) 90% confidence limit.

Table 8.3-12 presents the
factor 2/c^{2}_{p,d} for one-sided and two-sided
confidence limits, at six confidence levels for each. Multiplying the
appropriate factor by the observed total life T gives a confidence limit on
s. Figure 8.3-16
presents a graphical technique for determining upper and lower confidence
limits for tests truncated at a fixed time, when the number of failures is
known.

TABLE 8.3-12: FACTORS FOR
CALCULATION OF MEAN LIFE

CONFIDENCE INTERVALS FROM TEST DATA (FACTORS =
2/c^{2}_{P,D})