Intro to Statistics Critical Thinking

FOR #1:

You need the point-estimate, which is the mean. You will also need the standard deviation as you will be calculating confidence intervals.

LOWER LIMIT: MEAN - z ( Standard Deviation/ sq rt (N))

UPPER LIMIT: MEAN + z ( Standard Deviation/ sq rt (N))

For “z” , you use the z-value that corresponds to the level of confidence…. should be 1.96 for 95% confidence intervals and 1.645 for 90%.

FOR #2 and #3

You are still finding the same information from above, but using a Population proportion.

POINT ESTIMATE (p): Number of Successes/Total Number

The point estimate is what gets plugged in for “p” in the formula.

LOWER LIMT: p – z * sq rt [ (p(1-p))/n])

UPPER LIMIT: p + z * sq rt [ (p(1-p))/n])

For “z” , you use the z-value that corresponds to the level of confidence…. should be 1.96 for 95% confidence intervals and 1.645 for 90%.

QUESTION 4: Sample size

This site should help you.

Watch the second video under:

Sample Size Point Estimate Statistics

This video shows two examples on estimating a desired sample size based on predetermined margins of error.