In charlotte-ngs/asmss2022: Applied Statistical Methods in Animal Science - Spring Semester 2022

knitr::opts_chunk$set(echo = TRUE)

# define data directory depending on online status
if (params$isonline){
  s_data_dir <- "https://charlotte-ngs.github.io/asmss2022/data"
} else {
  s_data_dir <- file.path(here::here(), "docs", "data")
}
s_data_path <- file.path(s_data_dir, "asm_bw_mult_reg.csv")
s_data_bw_bc_path <- file.path(s_data_dir, "asm_bw_bc_reg.csv")
# write the default one variable regression, if we are not online
if (!params$isonline){
  tbl_mult <- readr::read_csv(file = s_data_path)
  tbl_bw_bc <- dplyr::select(tbl_mult, Animal, `Breast Circumference`, `Body Weight`)
  if (!fs::file_exists(path = s_data_bw_bc_path))
    readr::write_csv(tbl_bw_bc, file = s_data_bw_bc_path)
}
tbl_bw_bc <- readr::read_csv(file = s_data_bw_bc_path)
n_nr_obs <- nrow(tbl_bw_bc)

Problem 1: Measurement Unit

The measurement unit has an influence on the results of a regression model. This is demonstrated by changing the unit for Breast Circumference (BC) from centimeters to meters.

Tasks

• Read the original dataset with BC and BW for r n_nr_obs animals. The dataset is availble as csv-file under: r s_data_bw_bc_path
• Convert all values of BC from centimeters to meters
• Run the regression model using lm()
• Compare the results with the results from the original model

Your Solution

• Use the function readr::read_csv() to read the data

• Divide all values in column Breast Circumference by 100

• Run the regression using lm()

• Comparison of results

Problem 2: Significance Level

Do the same type of comparison of regression modelling results when changing the measurement unit for the variable HEI in the complete dataset given in

https://charlotte-ngs.github.io/asmss2022/data/asm_bw_mult_reg.csv.

Tasks

• Run the same regression model as in Problem 1 of Exercise 1
• Convert the measurement unit for the variable HEI from centimeter to meter
• Compare the results of the two regression models with a special focus on the significance level

Your Solution

• The same regression model as in Problem 1 of Exercise 1

• Convert the values in column HEI from centimeter to meter

• Fit again a multiple regression model

• Compare the results

cat('\n---\n\n _Latest Changes: ', format(Sys.time(), '%Y-%m-%d %H:%M:%S'), ' (', Sys.info()['user'], ')_\n', sep = '')

charlotte-ngs/asmss2022 documentation built on June 7, 2022, 1:33 p.m.