Day 2 - 08/21/2024

From last class

Think of your project topic!
Talk to us if you need data. Check out kaggle, Harvard Dataverse, this R package.
About R versus SAS, versus python…
Assignment 1 is due next Wednesday 28th.

Intro to statistical modeling

Mental checklist:

What is the problem or question? (what is the objective?)
How is the data generated?

Short story

My dad wants to grow clover in our farm and has different species to pick from.

How does the mental checklist look like?
1. What is the problem or question? (what is the objective?)
2. How is the data generated?

The data

We planted three different legume species and waited two months for them to grow.

source 1, 2, 3.

library(tidyverse)
library(car)

dd_lotus <- read.csv("data/lotus_part1.csv") %>% 
  transmute(species = factor(species), agb_g) 
summary(dd_lotus)

 species     agb_g      
 A:24    Min.   :1.265  
 C:24    1st Qu.:1.969  
 D:24    Median :2.355  
         Mean   :2.492  
         3rd Qu.:2.936  
         Max.   :4.354

dd_lotus %>% 
  ggplot(aes(species, agb_g))+
  labs(y = expression(Aboveground~Biomass~(g~plant^{-1})))+
  geom_boxplot()

dd_lotus %>% 
  ggplot(aes(agb_g))+
  labs(x = expression(Aboveground~Biomass~(g~plant^{-1})))+
  geom_histogram( fill = NA, color = "black")+
  theme_classic()+
  theme(aspect.ratio = 1, 
        panel.grid.major.x = element_line())+
  facet_wrap(~species)

Data generating process

To the whiteboard!

Fitting the model to data

Live R session

See code here.

For next class:

Read Chapter 2 from the book.
Think of your project topic!
Schedule a 15-min meeting and we can chat about your project.