Exercise 9. Comparing to actual results by pollster - multiple polls

Remake the plot you made for the previous exercise, but only for pollsters that took five or more polls.

You can use dplyr tools group_by and n to group data by a variable of interest and then count the number of observations in the groups. The function filter filters data piped into it by your specified condition.

For example:

data %>% group_by(variable_for_grouping) 
    %>% filter(n() >= 5)

This exercise is part of the course

HarvardX Data Science Module 4 - Inference and Modeling

View Course

Exercise instructions

Define a new variable errors that contains the difference between the estimated difference between the proportion of voters and the actual difference on election day, 0.021.
Group the data by pollster using the group_by function.
Filter the data by pollsters with 5 or more polls.
Use ggplot to create the plot of errors by pollster.
Add a layer with the function geom_point.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

# The `polls` object has already been loaded. Examine it using the `head` function.
head(polls)

# Add variable called `error` to the object `polls` that contains the difference between d_hat and the actual difference on election day. Then make a plot of the error stratified by pollster, but only for pollsters who took 5 or more polls.

Edit and Run Code