Exercise

# Confidence intervals

Polling data is not perfect. Most polls come with a reported "margin of error," or intervals around estimates that indicate how much true results could vary from sample proportions. In layman's terms, the margin of error is a standard 95% confidence interval around the estimated proportion.

When using polls to predict elections, we use a predictive margin of error, equal to the root-mean-square error (RMSE) of polling in previous years. You'll learn how to calculate and wrangle a variable for the margin of error in polls.

Instructions

**100 XP**

- Using the dataset you created in the last exercise, find the root-mean-square of the
`error`

variable. - Find the standard 95% confidence interval for polling by multiplying the RMSE times 1.96.
- Append that confidence interval, or "margin of error", to the dataset and save it to a new object,
`by_year`

.