Exercise

# Exercise 1 - Confidence Intervals of Polling Data

For each poll in the polling data set, use the CLT to create a 95% confidence interval for the spread. Create a new table called `cis`

that contains columns for the lower and upper limits of the confidence intervals.

Instructions

**100 XP**

- Use pipes
`%>%`

to pass the`poll`

object on to the`mutate`

function, which creates new variables. - Create a variable called
`X_hat`

that contains the estimate of the proportion of Clinton voters for each poll. - Create a variable called
`se`

that contains the standard error of the spread. - Calculate the confidence intervals using the
`qnorm`

function and your calculated`se`

. - Use the
`select`

function to keep the following columns:`state`

,`startdate`

,`enddate`

,`pollster`

,`grade`

,`spread`

,`lower`

,`upper`

.