This means sum all of the xi’s from i=1 to i=n. To keep things simple, when the
suffix i assumes all values in the range we use Σxi or simply Σx. The range of
values to be summed is indicated above and below sigma. So, with respect to the
five anxiety scores,Rules of summation:
is read as sum of all the squared values of xi, that is 5^2 +4^2 + 7^2 +9^2 +8^2 This is
equal to 235. However, means sum all the values of xi and then square this
value (5+4+7+9+8)^2. This equals 33^2 =1089.
Note The general rule, which always applies, is to perform
operations within parentheses before performing operations outside parentheses.
3 Order statistics
Should you want to specify the order of a set of values this is denoted by adding
small brackets around the subscript i, that is (i). In general form this would be x(1),
x(2)...x(n) where x(l) would be the smallest value in a set, i.e., rank of 1, x(2) would
be the second smallest value in a set, i.e., rank of 2 and so on. This implies that
x(1)≤x(2)≤...x(n) where ≤ means less than or equal to. For the set of 5 anxiety
scores,
x(1)=4, x(2)=5, x(3)=7, x(4)=8, and x(5)=9
Appendix 349