Introduction to Statistics (MAT/SST 115.03 2008S)

R notes for Activity 27-6: Exam Score Improvements


Okay, more data. Let's load it in.

ExamScores = read.csv("/home/rebelsky/Stats115/Data/ExamScores.csv")

They wouldn't give us more NA values, would they?

> summary(ExamScores)
    Student       Exam1           Exam2      
 S01    : 1   Min.   :72.00   Min.   :50.00  
 S02    : 1   1st Qu.:82.25   1st Qu.:68.50  
 S03    : 1   Median :88.50   Median :80.00  
 S04    : 1   Mean   :87.38   Mean   :78.65  
 S05    : 1   3rd Qu.:95.00   3rd Qu.:91.00  
 S06    : 1   Max.   :98.00   Max.   :97.00  
 (Other):18                   NA's   : 1.00  

Yes, I guess they would. Let's get rid of it.

ExamScores = na.omit(ExamScores)

27-6 a. Scatterplots

plot(ExamScores$Exam1, ExamScores$Exam2)

27-6 b. Yet another correlation cofficient

You should be able to compute this one on your own.

27-6 d. Changing exam 1 grades.

You can change the exam 1 grades en masse with

ExamScores$Exam1 = ExamScores$Exam1 - 10

27-6 f. Changing exam 2 grades

If you look at 27-6 d., you should be able to figure out how to double the grades on exam 2.

27-6 h. Making up data

exam1 = c(...)
exam2 = exam1 + 10
plot(exam1, exam2)
cor(exam1,exam2)

27-6 j. Making up data

We can continue to use the exam 1 grades from part h. We just need to change the way we compute the exam 2 grade.

exam2 = exam1 * 2
plot(exam1, exam2)
cor(exam1,exam2)

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Samuel A. Rebelsky, rebelsky@grinnell.edu

Copyright (c) 2007-8 Samuel A. Rebelsky.

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