# Stat 301 – HW 9 answers

```Stat 301 – HW 9 answers
1. Chimp learning
a. 1 pt. F = 7.76, p &lt; 0.0001
b. 1 pt. very strong evidence that at least one word takes a different amount to time to learn.
c. 1 pt. longest time: string: mean = 5.65, 95% ci: (4.82, 6.48)
d. 1 pt. 0.404
e. 1 pt. 0.438
f. 1 pt. Yes, blocking by chimp is a good idea – it increases the precision of comparisons among words.
2. Iridium at the Cretaceous – Tertiary transition
a. 2 pts. Removed from the HW. My question was not worded carefully enough.
b. 1 pt. F = 1.03, p-value = 0.43. no evidence of an interaction between rock type and depth category.
c. 1 pt.
d. 1 pt. The lines for shale and limestone are roughly parallel.
Depthcat 3 has a sharp peak in both shale and limestone.
e. 1 pt. F = 12.63, p-value &lt; 0.0001.
Very strong evidence that at least one depth category has a different mean Iridium concentration.
f. 1 pt. From depth 1 to depth 6, lsmean Iridium concentrations are: 222, 265, 623, 306, 146, 123
g. 1 pt. (329, 624)
3. Missing work
b. 1 pt. Two things jump out at me: the relationship looks curved and there is one observation with a
very large Y value for its X value.
c. 1 pt. Clear reason to remove the outlier.
Note: In terms of the 3 step approach in class, you are restricting the population to currently working
employees.
d. 1 pt. Cook’s D is 0.42.
Note: This large, but not so large to indicate that the observation substantially changes the predicted
values.
e. 1 pt. The regression coefficients change from 223 and -9.60 to 191 and -9.58. The rMSE drops
substantially, from 131 to 39.4. As a consequence, the standard errors of the regression coefficients are
much smaller and the p-value for the test of slope = 0 drops from 0.33 to 0.0058.
Note: The standardized residual for observation 13 is 3.4, which is very large, especially with only 15
observations.
```