Covariance by hand
In R, you can quickly compute various statistical measures using functions. The interviewer might be interested if you can replicate the calculations of these functions to ensure your understanding of what the functions do.
In this exercise, you will compute covariance by hand. The covariance measures the variability of two random variables.
Recall that the formula for the covariance of a sample is:
\( \sum_{i=1}^{n} \frac{(x_i - \overline{x})(y_i - \overline{y})}{n-1}\)
The df
data frame is available in your environment with variables x
and y
.
This exercise is part of the course
Practicing Statistics Interview Questions in R
Exercise instructions
- Assign the number of observations in
df
ton
. - Compute the covariance between
x
andy
by hand. - Compute the covariance between
x
andy
using a function from thestats
package.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# The number of observations
___ <- nrow(___)
# Compute covariance by hand
___((df$x-___(df$x))*(___-mean(df$y)))/(___-1)
# Compute covariance with function
___(df$x, ___)