Exam 2 review

Lecture 23

Dr. Mine Çetinkaya-Rundel

Duke University
STA 199 - Fall 2022

11/17/22

Warm up

Announcements

• Exam 2 is released on today at noon and is due at 2pm on Monday.

  • No TA OH during the exam.

  • I will have OH 4-5pm on Friday (on Zoom).

  • Any clarification questions must be emailed to me only.

  • No Slack use during the exam, even about non-exam related questions.

• Answer keys:

  • HW 4 and HW 5 feedback: Keys both posted, feedback coming soon.

  • All lab keys also posted.

  • AE 16 key missing complete answers, will post after class.

Review questions

Questions: Grouping

Does order of variables in group_by() matter?

library(palmerpenguins)
library(tidyverse)

penguins |>
  group_by(species, sex) |>
  summarize(mean_bm = mean(body_mass_g))

# A tibble: 8 × 3
# Groups:   species [3]
  species   sex    mean_bm
  <fct>     <fct>    <dbl>
1 Adelie    female   3369.
2 Adelie    male     4043.
3 Adelie    <NA>       NA 
4 Chinstrap female   3527.
5 Chinstrap male     3939.
6 Gentoo    female   4680.
7 Gentoo    male     5485.
8 Gentoo    <NA>       NA 

penguins |>
  group_by(sex, species) |>
  summarize(mean_bm = mean(body_mass_g))

# A tibble: 8 × 3
# Groups:   sex [3]
  sex    species   mean_bm
  <fct>  <fct>       <dbl>
1 female Adelie      3369.
2 female Chinstrap   3527.
3 female Gentoo      4680.
4 male   Adelie      4043.
5 male   Chinstrap   3939.
6 male   Gentoo      5485.
7 <NA>   Adelie        NA 
8 <NA>   Gentoo        NA 

Questions: Factors

• When will we use factors and how does that make a difference in the data?

• When do you use fct_relevel() versus fct_reorder()?

• How to use case_when() function and the proper use of forcats functions like fct_relevel() , fct_reorder(), fct_other()?

Review: https://r4ds.hadley.nz/factors.html.

Questions: LaTeX / equations

• What is the name of the math symbol text we use to write equations? Is there a cheat sheet with the shortcuts for each symbol?
• Do we have to use LaTeX for our equations?

\(H_0:\mu_1 - \mu_2 = 0\)

\(H_A: \mu_1 - \mu_2 \ne 0\)

$H_0:\mu_1 - \mu_2 = 0$

$H_A: \mu_1 - \mu_2 \ne 0$

H0: mu1 - mu2 = 0

HA: mu1 - mu2 ≠ 0

Questions: Ethics

Would love to review data ethics and how to answer questions about ethical issues with any dataset.

Review: The videos from the Ethics module.

Questions: Miscellaneous

What does geom_smooth(method = “loess”) do?

Fits a non-linear model to the data, a smooth curve.

How do we know how much to round by?

Round as much as it makes sense in the context of the data. Avoid rounding in interim steps.

Question: Inference

How do we decide whether to use bootstrap, simulate, or permute in the generate() step of inference?

• Bootstrap: For constructing bootstrap intervals or for testing for a single mean (\(H0: \mu_0 = 5\))

• Simulate: For testing for a single proportion (\(H_0: p_0 = 0.3\))

• Permute: For testing for independence, i.e., for testing for differences in means or proportions across groups (or whether one is less/greater than the other)

Application exercise

ae-19

• Go to the course GitHub org and find your ae-19 (repo name will be suffixed with your GitHub name).
• Clone the repo in your container, open the Quarto document in the repo, and follow along and complete the exercises.
• You should have already pushed updates on Tuesday, so you should be good for submission.