D

1) How does one determine the minimum sample size to use for a Weibull? There are equations for calculations the sample size for a mean e.g n = Z^2 * sigma^2 / sampling_error^2. This seems to work well when your standard deviation is small but with failure data the standard deviation is typically large and on occasion not normally distributed. This equals huuuuuuge sample sizes using this method. Should I use a proportions method? The sample size is still large.

2) I would like to plot the remaining 21 data points over the CDF calculated from my first 5 points. The median ranking has a huge effect on this, so what is the correct way to do this? I have used 2 methods. Beta cumulative probability density function (first step in calculating the MR for any data set) and the second using the regression values for the set of 21 data (used to calculate the MR). The data is closest to the 5 point CDF is the beta cumulative probability density function but I intuitively think the regression method makes the most sense since. Is there a way to do this?

Here is my data set.

154173

171158

83431

201778

117578

192083

136262

149487

148009

98317

69798

94195

62548

103574

108364

132377

143047

85272

95760

214166

289237

161265

172490

99972

117440

89717