Minitab Notes for Activity 4

Constructing a Confidence Interval for a Proportion (Question 5)

  1. Go to Stat / Basic Statistics / 1 Proportion
  2. Click on the Summarized data radio button
  3. Enter 50 for the number of trials
  4. Enter the number of strawberry (pink wrapper) candies that you found in your bag for the number of successes.
  5. Click on Options.
    1. Make sure the confidence level is set to 95 (for 95%)
    2. Check the box for "Use test and interval based on normal distribution"
    3. Click OK
  6. Click OK

Note that the confidence interval will appear as ( #### , #### ) where there ####'s are the lower and upper limits of the interval. These are given as proportions (decimals) not percents. If you convert them to percents, be sure to write the % sign after them. If the computer says (0.3215,0.6521), then write it on your paper as (preferred) "0.3215 < p < 0.6521" or (acceptable)"32.15% < p < 65.21%".

Hypothesis Test (Question 8)

The place to test the hypothesis that 35% of the candies are strawberry is from the same procedure we just used to find the confidence interval. The only differences are in the Options screen.

We want to test a proportion of 0.35 (35%), not 0.5 (50%), so change that. Also, for this part of the question, we want the Alternative to be "not equal" (which is should be), but we will change that later.

Completing the Sentences (Question 8c)

The probability value (p-value) is the chance of getting the results we obtained if the null hypothesis is true. For our data, that means the chance of getting your results if the true percentage of strawberry candies is 35%. Some of the sentences will require you to re-run the hypothesis test after changing the alternative hypothesis under Options.

Here are some guidelines to help you answer the sentences.