Standard Deviation



Standard Deviation

Steps

1. Average the results of you tests.

2. Subtract the average from each result.

3. Square all of your results from step 2.

4. Add all of the new result numbers.

5. Divide that new number by the number of trials minus one. (if you have five trials you will divide by 5 – 1 = 4)

6. Find the square root of that new number.

Example:

|TRIAL |RESULT |

|1 |2 |

|2 |4 |

|3 |6 |

|4 |8 |

|5 |5 |

Step 1: Average the results.

2 + 4 + 6 + 8 + 5 = 25

25 ( 5 = 5

Step 2: Subtract the average from each result.

2 – 5 = -3

4 – 5 = -1

6 – 5 = 1

8 – 5 = 3

5 – 5 = 0

Step 3: Square all of your results.

-3² = 9

-1² = 1

1² = 1

3² = 9

0² = 0

Step 4: Add all of the new result numbers.

9 + 1 + 1 + 9 + 0 = 20

Step 5: Divide that new number by the number of trials minus one.

20 ( (5-1)

20 ( 4 = 5

Step 6: Find the square root of that new number.

±√5 = ±2.2

The standard deviation is ±2.2. This means that when evaluating your results the margin of error is ±2.2 in either direction. Anything outside of this range would be considered insignificant.

If you have Excel and with to use its standard deviation graph, after creating the spreadsheet, choose STDP when running the graph.

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