Exercise

# Beak length to depth ratio

The linear regressions showed interesting information about the beak geometry. The slope was the same in 1975 and 2012, suggesting that for every millimeter gained in beak length, the birds gained about half a millimeter in depth in both years. However, if we are interested in the shape of the beak, we want to compare the *ratio* of beak length to beak depth. Let's make that comparison.

Remember, the data are stored in `bd_1975`

, `bd_2012`

, `bl_1975`

, and `bl_2012`

.

Instructions

**100 XP**

- Make arrays of the beak length to depth ratio of each bird for 1975 and for 2012.
- Compute the mean of the length to depth ratio for 1975 and for 2012.
- Generate 10,000 bootstrap replicates each for the mean ratio for 1975 and 2012 using your
`draw_bs_reps()`

function. - Get a
**99%**bootstrap confidence interval for the length to depth ratio for 1975 and 2012. - Print the results.