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← SD Social Networkers - Intro to Descriptive Statistics

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Showing Revision 4 created 06/27/2017 by Dejan Trajkovic.

  1. >> I'm going to show you the answer to this, by doing it in a spreadsheet. You
  2. could do all of these calculations, without any technology. And if you did that,
  3. that's really great. It's always really good practice to calculate things
  4. without using any technology, but just for the purposes of figuring out the
  5. standard deviation, technology can really speed along this process. So I'm not
  6. going to use any shortcuts here. We're going to do it exactly as we would if we
  7. didn't have technology. So first we need to take the avearage of all of these,
  8. we're going to sum them up. So we're taking the sume of all of these. I could
  9. also just write equals a1 plus a2 plus a3 all the way to a10. And we'd get the
  10. same thing. But why would we do that if we can simply write this. Now to take
  11. the average all we do is divide by the number of values which is 10. So that's
  12. just going to be 51,511.1. Alternatively, the nice thing about technology is we
  13. can just do this. Take the sum, and divide by the total number. Do it all in 1
  14. step. So now we have the average. Now we're going to subtract the average from
  15. each 1 of these values. Not the opposite, where we subtract each of these values
  16. from the mean. That's an important distinction. In this case, it doesn't matter
  17. as much but in other statistical concepts that's an important distinction to
  18. make. So we'll write equals A1 minus. The mean. So I'm subtracting the mean from
  19. each of these values. Now I could just do the same thing here and write equals
  20. a2 minus the mean but that would be tedious. We can just drag this down. When
  21. you do that, remember that there has to be a little plus sign there. That means
  22. you're successfully dragging it down. If you went like this, it won't do
  23. anything. It'll just highlight the boxes. So here, we have the deviations from
  24. the mean. Here, in the next column We're going to square each deviation. Equals
  25. b1 squared. And again, we're going to drag it down. So we have the squared
  26. deviations for each of these values. Now remember that the variance is the
  27. average squared deviation. So we could just write. Average of c1 to c10. But I
  28. want to make sure we go through all the other steps in between. So let's again
  29. practice calculating the average just for clarity's sake. So the variants then
  30. would be the sum of c1 to c10. Remember that's how you start out taking the
  31. average, and then divide by 10. So here's the variance, and then the standard
  32. deviation is simply the square root of the variance. So we'll write equals SQRT.
  33. That's the shortcut for square root. And then we can just see C13. So we know
  34. that the standard deviation is 6557.16 approximately. Now I want to point out
  35. something really important before we finish this solution video. Here I simply
  36. said equals square root of this cell C13. Whereas here, I wrote out the
  37. whole average. The reason for that is because say I had but this all here, A13.
  38. Then, when we drag it down, we don't get the right deviations. And we can double
  39. click on it, and see what it did. Here, it took A4 minus A16, whereas here it
  40. took A1 minus A13, which is what we wanted. But we want it to always stay A13,
  41. which is why we have to make sure this is a constant. And the way to make sure
  42. it's a constant is by just writing it. Notice also that all of these values
  43. changed when these values changed because all these values are dependent of
  44. these values So when we change it back we should again get the correct standard
  45. deviation.