Confidence intervals for means and proportions

STA 121. Practice questions, not past papers.

Lessons

• Interpret and construct intervals
• Proportions and differences

Practice questions

1. A confidence interval's margin of error equals what?

   Statistics study edition practice item Q286; Source: T125-128, T132-133

2. A 95% frequentist confidence level describes what?

   Statistics study edition practice item Q287; Source: T125-128, T132-133

3. For the same data, increasing confidence generally does what to interval width?

   Statistics study edition practice item Q288; Source: T125-128, T132-133

4. When σ is unknown and a normal small-sample mean model is appropriate, use which multiplier?

   Statistics study edition practice item Q289; Source: T125-128, T132-133

5. A mean interval uses known σ=10, n=100, sample mean=50 and z=1.96. Find its lower endpoint. Give the value to 4 decimal places.

   Statistics study edition practice item Q290; Source: T125-127

6. A mean interval uses known σ=8, n=64, sample mean=30 and z=1.96. Find its lower endpoint. Give the value to 4 decimal places.

   Statistics study edition practice item Q291; Source: T125-127

7. A mean interval uses known σ=6, n=36, sample mean=20 and z=1.96. Find its lower endpoint. Give the value to 4 decimal places.

   Statistics study edition practice item Q292; Source: T125-127

8. For independent proportions 30/1000 and 100/1200, find the upper endpoint of the 95% Wald interval for p1-p2, using z=1.96. Give the value to 4 decimal places.

   Statistics study edition practice item Q293; Source: T133 exercise 7

9. Interval width equals _____ times its margin of error.

   Statistics study edition practice item F095; Source: T125-128, T132-133

10. A confidence level describes repeated-sampling _____.

    Statistics study edition practice item F096; Source: T125-128, T132-133

Topic gap report