SFU Beedie courses only. See the course list →
Business TutorBusiness Tutor
← Everything for BUS 232
BUS 232

How precise is your estimate?

Turn a sample into a useful range. Build confidence intervals for means and proportions, choose the sample size you need, and see what confidence really means.

Estimating a mean · Step 1 of 16

One estimate needs a measure of uncertainty

Average flight tickets
135.00140.00145.00150.00155.00population value
Point estimate: 145.50Interval: 137.10 to 153.90
A point estimate is one sample number used to estimate a population number: x̄ estimates the mean μ; p̂ estimates the proportion p. A point alone says nothing about precision. An interval estimate adds a range. A reported unemployment rate of 4.10%, with a 90% interval from 3.95% to 4.25%, does not establish a fall from a 4.20% benchmark.
Try it: Switch between a mean and a proportion. Both have a point in the middle and uncertainty on either side.
What are we estimating?
Point estimate
145.50
Margin of error
8.40
x̄ = (sum of observations) / n; p̂ = successes / n. Interval = point estimate ± margin of error.

In Excel: =AVERAGE(A1:A35)

Check yourself
What does a point estimate leave out?

Need help choosing z, t or a sample size?

Bring your problem sets. We work through them together until every type feels routine.

FAQ

Questions, answered.

Still unsure about something? Message us and you will hear back within a day.

See all questions
  • In person, we meet at the SFU Burnaby campus or in a private meeting room near Brentwood in Burnaby. Online sessions run on Zoom. You choose when you book.