Homework 1

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This homework is due on Jan. 23, 2018 at 7:00pm. Please submit as a pdf file on Canvas.

This homework uses the Alfalfa data set. This data set contains the height of alfalfa sprouts after four days (Ht4) grown indoors in different acidic environments (Acid). There are three different amounts of acid observed in the data set: none (water), moderate (1.5HCl), and strong (3.0HCl). Each treatment was performed on 5 plants. The data set also contains information on the amount of daylight the plants received (Row). This column contains values a through e, where a indicates the row farthest from the window and e indicates the row closest to the window.

Alfalfa <- read.csv("http://wilkelab.org/classes/SDS348/data_sets/Alfalfa.csv")
head(Alfalfa)
##    Ht4   Acid Row
## 1 1.45  water   a
## 2 2.79  water   b
## 3 1.93  water   c
## 4 2.33  water   d
## 5 4.85  water   e
## 6 1.00 1.5HCl   a

Problem 1: (4 pts) We are interested in testing the effects of acidic environment on plant growth. Since there are three different amounts of acidity in the data set, and therefore three groups of acid measurements, we will use an analysis of variance (ANOVA) test. Conduct an ANOVA test and interpret your results in 1-2 sentences. HINT: You will first need to create a linear model object using the lm() function before you can use the anova() function.

# R code goes here

Your answer goes here. 1-2 sentences only.

Problem 2: (3 pts) Create a boxplot of the plant growth, separated by acid amounts. Based on this plot, is the mean height of alfalfa grown in 3.0HCl the same or different from the mean height of alfalfa grown in water? Explain your answer.

# R code goes here

Your answer goes here. 1-2 sentences only.

Problem 3: (3 pts) Use a t test to determine if the mean height of plants grown in 3.0HCl is the same or different from the mean height of plants grown in water. Interperet and explain your results in 1-2 sentences.

# R code goes here

Your answer goes here. 1-2 sentences only.