Precision in Estimates of Treatment Effects

Question 1

What is a confidence interval?

Answer 1

A range of values which quantifies the imprecision in the estimate of a particular value

Specifically, it quantifies the imprecision that results from random variation in the estimation of the value. Doesn’t include imprecision resulting from systemic error (bias)

Question 2

How do we interpret confidence intervals?

Answer 2

1. Does interval contain value that implies no change/no effect/no association?
   
   1. If confidence interval is for a ratio measure, look to see if interval contains 1.0
   2. If confidence interval is for measure of absolute change/difference look to see whether that interval includes a 0
2. Is confidence interval wide or narrow?
   
   1. If it’s narrow, results precise
   2. If wide, results imprecise - Generally indicates inadequate sample size
   3. What are the upper and lower limits? (Ties in with clinical implications of any potential effect)

Question 3

Describe sampling bias

Answer 3

Sample selected in way that individuals choses NOT representative of whole study population

Question 4

What’s the difference between accuracy and precision?

Answer 4

Accuracy - How close is your data to the correct answer

Precision - How close are your results to each other, is there inherent error associated with any estimate

Question 5

How does interpretation for a confidence interval differ between ratio and absolute differences?

Answer 5

1. If confidence interval is for a ratio measure, look to see if interval contains 1.0
2. If confidence interval is for measure of absolute change/difference look to see whether that interval includes a 0