Short Answer

A psychology researcher measures the number of tasks completed by a small group of N=2N=2 participants, obtaining scores of 4 and 8. Using the formula SD=(XM)2NSD = \sqrt{\frac {\sum (X-M)^2}{N}}, compute the standard deviation (SDSD) for this dataset and write down each step of your calculation.

Question: A psychology researcher measures the number of tasks completed by a small group of N=2N=2 participants, obtaining scores of 4 and 8. Using the formula SD=(XM)2NSD = \sqrt{\frac {\sum (X-M)^2}{N}}, compute the standard deviation (SDSD) for this dataset and write down each step of your calculation.

Sample answer: First, calculate the mean: M=(4+8)/2=6M = (4 + 8) / 2 = 6. Second, find the difference between each score and the mean: 46=24 - 6 = -2 and 86=28 - 6 = 2. Third, square these differences: (2)2=4(-2)^2 = 4 and 22=42^2 = 4. Fourth, sum the squared differences and find their mean: (4+4)/2=8/2=4(4 + 4) / 2 = 8 / 2 = 4. Finally, take the square root of that mean: SD=4=2SD = \sqrt{4} = 2.

Key points:

  • Calculate the mean (M=6M = 6).
  • Subtract the mean from each score and square the results (44 and 44).
  • Find the mean of the squared differences (44).
  • Take the square root to calculate the standard deviation (SD=2SD = 2).

Rubric: The answer must show the correct intermediate calculations (mean M=6M = 6, squared deviations of 4 and 4, mean of squared deviations of 4) and provide the correct final standard deviation of 2.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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