Point Estimates and Margin of Error

A confidence interval gives all plausible values of the population parameter you are trying to estimate

• TRUE

• FALSE

• I HAVE NO IDEA

How do you interpret a confidence interval?

• There is a 95% chance the the interval from ____ to ____ contains the population parameter.

• 95% of the data values are in the interval from _____ to _____.

• I am 95% confident that the interval from _____ to _____ captures the true value of the population parameter.

• I am 95% confident that the sample statistic is in the interval from _____ to _____.

The general form of a confidence interval is

• point estimate x 2

• point estimate + margin of error

• point estimate - margin of error

• point estimate +/- margin of error

Given a confidence interval, how do you determine the value of the point estimate?

• Find the middle of the interval - (lower value + upper value)/2.

• Find the range of the interval and divide by 2.

• Use the lower end of the interval.

• You can't determine the point estimate from the confidence interval.

If a proposed value of the population parameter is not captured in the confidence interval, there is convincing evidence that that proposed value is incorrect.

• TRUE

• FALSE

A local pizza shop claims that they deliver pizzas in 30 minutes or less. The 95% confidence interval obtained from a random sample of 12 deliveries is [26.8,41.0].

Calculate the point estimate used to create this interval.

• 7.1 minutes

• 13.4 minutes

• 33.9 minutes

• 30.7 minutes

Answer explanation

(26.8 + 41)/2 = 33.9

A local pizza shop claims that they deliver pizzas in 30 minutes or less. The 95% confidence interval obtained from a random sample of 12 deliveries is [26.8,41.0].

Calculate the margin of error used to create this interval.

• 7.1 minutes

• 13.4 minutes

• 33.9 minutes

• 30.7 minutes

Answer explanation

(41 - 26.8)/2 = 7.1

A local pizza shop claims that they deliver pizzas in 30 minutes or less. The 95% confidence interval obtained from a random sample of 12 deliveries is [26.8,41.0].

Is there evidence to suggest that the stated mean delivery time is 30 minutes or less is incorrect?

• No. There are values in the interval that are 30 or less, so it is plausible the the pizza shop is making a valid claim.

• Yes. There are values higher than 30 in the interval which means that the pizza shop is delivering pizzas in more time than 30 minutes.

• No. The interval does not contain 30, so this value must be incorrect.

Answer explanation

(41 - 26.8)/2 = 7.1

A magazine reported that 66% of dog owners greet their dog before their spouse of children when they arrive home.

A random sample of 40 dog owners was obtained and a 95% confidence interval was calculated as [0.68, 0.78].

Calculate the point estimate that was used to create this interval

• 78%

• 5%

• 73%

• 66%

A magazine reported that 66% of dog owners greet their dog before their spouse of children when they arrive home.

A random sample of 40 dog owners was obtained and a 95% confidence interval was calculated as [0.68, 0.78].

Calculate the margin of error that was used to create this interval

• 78%

• 5%

• 73%

• 66%