# Lec29 Standard Errors Part II

### More on standard errors.

### Recall

**Thought Experiment**: Sample 3 students at random and get their (sample) mean age. Do this~~many, many, many~~only 3 times**Question 1**: Why do the sample means below vary?**Answer 1**: Because of the sampling variability induced by the random sampling!**Question 2**: What value quantifies how much these sample means vary by?**Answer 2**: The Standard Error!

Random Sample | (Sample) Mean Age |
---|---|

Jack, Jared, Sam | 21.7 |

Wengel, Rebecca, Steven | 19.4 |

Stefan, Joccelyn, Sierra | 20.0 |

### Announcements

- PS-10 Discussion.
- Regular lecture during lab time tomorrow.
- Doodle Poll to fill 11 time slots to discuss projects, as a group.

### In-Class

**Learning checks**: Based on

- the example in the Lec27-B learning check discussion
- the chalk talk notes from Lec28

- Explicity compute the
**standard error**when taking samples of size`n=5`

and`n=50`

. - Discuss with your peers
**why**they matter in any study that involves some kind of sampling.