- (a) Define a statistic.
A random sample \(X _ { 1 } , X _ { 2 } , \ldots , X _ { \mathrm { n } }\) is taken from a population with unknown mean \(\mu\).
(b) For each of the following state whether or not it is a statistic.
- \(\frac { X _ { 1 } + X _ { 4 } } { 2 }\),
- \(\frac { \sum X ^ { 2 } } { n } - \mu ^ { 2 }\).