Lesson 7.4 – Confidence Intervals for a Proportion

  • Use the four-step process to construct and interpret a confidence interval for a population proportion.
  • Determine the sample size required to obtain a C% confidence interval for a population proportion with a specified margin of error.


Activity: How much of the Earth is covered by water? 

Today we’re going to introduce the four step process: State, Plan, Do and Conclude.  We’ll be using this for the rest of the year so really stress it’s importance.  Memorizing the parts now will help students to be successful later.  We’ve created a 4 Step Confidence Intervals Template to use.  Students will use it as they’re memorizing and practicing, but by time they get to the test they will not be allowed to use it.

We’re going to estimate the proportion of the Earth that is covered by water.  To do this, the students will toss a globe around the room to each other.  We used this inflatable globe.  When they catch it, they need to call out if the tip of their right thumb is on land or water.  You should track this on the board while they do this.  We had students stand until they caught the globe twice, then they sat down.  We had them catch twice to make sure that the Large Counts condition was met.  You should try to get around 50 catches.  Once this process is done, the groups will use the data to calculate a confidence interval.  They should be able to complete the entire activity without teacher input using their notes from lesson 7.3 if needed.


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