Question

Many traffic experts argue that the most important factor in accidents is not the average speed of cars but the amount of variation. Suppose that the speeds of a sample of 200 cars were taken over a stretch of highway that has seen numerous accidents. Compute the standard deviation of the speeds in Excel file Q-14.xlsx.

Answer 1

Answer and Step-by-step explanation: Standard Deviation is the measure of how diferent a number is from the mean of the data set. It is the spread of a data set. To calculate it manually:

1) Find the mean of the data set. Mean, represented by μ, is the sum of all the values divided by the total number of elements forming the set;

2) Subtract each number with the Mean and square the result;

3) Add the differences and divide it by the total number of elements of the set;

4) Take the square root of the result and that is the Standard Deviation.

The calculations can be done by a calculator like Excel:

1) In each cell of a same column, write the data you want to know the deviation.

2) On the last cell, write: =stdev.p(A1:A10) or =stdev.s(A1:A10).

3) Press Enter. The deviation will appeared on the same cell.

The function STDEV.P is used when the data represents the entire population, whereas STDEV.S is used when the data is for a sample of the population. Inside the parenthesis, put the cells where your data is. For example, if you put your data in the column A, from cell 1 to cell 10, you write like it's written above.