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← Rent - Increase n - Intro to Inferential Statistics

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Showing Revision 5 created 05/25/2016 by Udacity Robot.

  1. If our sample size is 100, that means we now have 99 degrees of freedom instead
  2. of 24. And if we look at our T table, we see that the closest degrees of
  3. freedom to 99 is 100. So we'll just use that one. And again we want .025 in
  4. each tail. Notice that it also says at the bottom Confidence level C. And here
  5. we have 95%. This is the same as how at the top of the column, it has .025% in
  6. either tail. That's equivalent to a 95% confidence interval, pretty cool. And
  7. we see that the t critical value is 1.984 and negative 1.984. Therefore, the
  8. margin of error is 1.984 times s, divided by root n. And this is 39.68. Notice
  9. that now the margin of error got a lot smaller than it was before with a sample
  10. size of 25. Before the margin of error was 2.064 times 200 divided by the
  11. square root of 25, which was 82.56. So when we increase the sample size, we
  12. decrease our margin of error, and we're more precise. And remember, when we
  13. increase the sample size, we also have more degrees of freedom and therefore,
  14. our t distribution goes from wider to skinnier as it approaches normality.