A First Course in Quality Engineering, 2nd Edition

114 A First Course in Quality Engineering

2.6.1 Definitions

A sample of n units drawn from a population produces n observations {X

1

,

X

2

,…, X

n

}� This set of n observations is identied as “the sample” for further

mathematical work� It is easy to see that each element of the sample is a

random variable having the same distribution as the population� In addi-

tion, we assume that the observations are independent� Thus, a sample of

size n is a collection of n independent, identically distributed (I�I�D�) ran-

dom variables� When we pick a sample (of physical units) in practice and

take measurements on them, we get one set of observations ...