One hundred teachers attended a seminar on mathematical problem solving. The attitudes of a representative sample of 15 of the teachers were measured before and after the seminar. A positive number for change in attitude indicates that a teacher's attitude toward math became more positive. The 15 change scores are as follows: 3; 8; -1; 2; 0; 5; -3; 1; -1; 6; 5; -2; 4; -3; 7

What is the standard deviation for this sample?

2.00

2.07

3.67

-1.00