5 2 Bias Variability Bias Variability Bias is

5. 2 Bias & Variability

Bias & Variability • Bias is consistent, repeated deviation of the sample statistic from the population parameter – Low Bias = High Accuracy – High Bias = Low Accuracy • Variability is how well you are able to reproduce the same results between repeated samples – Low Variability = High Precision – High Variability = Low Precision

Bias & Variability True parameter = 35%, identify each results as high/low bias & high/low variability • 52%, 55%, 51%, 54%, 55% High Bias, Low Variability • 48%, 29%, 27%, 43%, 20% Low Bias, High Variability • 48%, 63%, 71%, 52%, 59% High Bias, High Variability • 33%, 36%, 37%, 33%, 34% Low Bias & Variability Ideal Situation

Bias & Variability How do you reduce variability? Larger Sample Size Matched Pairs How do you reduce bias? Improve Sampling Method Increase Randomness

Matched Pairs • In an experiment you have two groups, those that you apply a treatment to (experimental group) and those you don’t (control group). • Normally you randomly assign people between the two groups. • Matched Pair Design: – Find out a lot of information about your subjects – Pair them up so each pair contains 2 people with many similar qualities – Split the pair up, randomly deciding which goes to the control group and which to the exp. group