The following hypothetical data were obtained from a random sample of nine college freshmen. They represent attitude scores toward a statement made by the President, "The economy has improved in the last 12 months". Scores ranged from 9 (strongly agree) to 1 (strongly disagree). The investigator was interested in estimating the variability of attitudes among this year's entire freshman class on this question.

3 7 7 9 4 6 2 7 6

Calculate the appropriate index of standard deviation for the above investigation.