Confidence Interval

Even though the difference is not statistically significant, let's practice interpreting a confidence interval.

(t) First, use the 2SD method to approximate a 95% confidence interval:

  • What value did the applet give you for the standard deviation of the null distribution?
  • Extend that distance on each side of the observed statistic.
lower bound = observed difference - 2 SD
upper bound = observed difference + 2SD

(u) Use the applet to determine the theory-based confidence interval.

  •  At the bottom of the first column in the applet, check the box to display 95% CI(s) for difference in proportions
  • Take a screen shot of your results and add to your report.

Are the intervals similar?

Rememberm to interpret the interval as the difference in probabilities, indicating the direction and the size of the difference. This is a bit tougher when zero is in the interval!

We are 95% confident that
is up to than
is up to than

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