Confidence Intervals for Slope (Topics 9.2-9.3)

Chapter 12 - Day 2

Learning Targets
  • Interpret the values of a, b, s, and SEb in context, and determine these values from computer output.

  • Construct and interpret a confidence interval for the slope of the population (true) regression line.

Activity: Does Seat Location Matter? Part 2
Answer Key:

Construct a confidence interval. Easy!

This is where all of our hard work training students with the 4-step process really pays off. The general formula for a confidence interval is always the same:

Point Estimate +/- Margin of Error

The specific formula for this confidence interval is easy if you know what you're trying to estimate (slope):

b +/- t* SEb

The only new idea students need to know here is that df = n - 2.

What about all these conditions?

Checking conditions here does provide a good opportunity to review some important ideas (residual plots, 10% condition, random sample vs. random assignment), but it is very unlikely that students will be asked to check conditions for linear regression inference on the AP Exam (watch this be the investigative task this year). 


Should I take students through the calculation for SEb?

No. Have them find this value in the computer output.

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