Confidence Intervals

Question 1

what does a confidence interval tells us?

Answer 1

how wrong could we be?

Question 2

what is the confidence interval?

Answer 2

the range above/below the finding of the study which gives us a ‘margin or error’

the true value probably lies in this region 95% of the time

Question 3

what was the risk of PET in the sample?

How much lower could it be in reality in the population?

how high could it be in the population?

how likely is it that the real risk is outside of this range (above/below)?

Answer 3

•What was the risk of PET in the sample?

–5.3%

•How much lower could it be, in reality, in the population?

–As little as 3.4%

•And how high could it be?

–As high as 8.0%

•How likely is it that the real risk is outside this range, above or below?

–Just 5%

Question 4

Look at the follwoing data and determine

• the difference between means - what does this actually tell us/
• the confidence interval- what does this actually tell us?

Answer 4

•Smokers’ babies were 247 grammeslighter

–3,220 g against 3,460 g

–That’s equivalent to a week of gestational development!

•The confidence interval is 133 to 361 grammes

–So smoking in this population is likely to reduce baby weight by at least 133 and as much as 361 grammes