Assessment Test 01
Goal:
Assessing your understanding about basic numerical summaries, grapjical
displays
and connection between them.
Questions
Refer to the (partial) output and answer the following questions.
1. Calculate the values of (1), (2), (3), (4), (5).
(Hint: The stem-and-leaf plots for midterm and final are given. Therefore,
you essentially know the whole data set.)
2. Identify min, max, Q1, median, Q3 of mid and final in the stem-and-leaf
plots and histograms (which category they belong to).
3. How are midterm scores and final scores different from each other?
Use the numerical summaries and graphical summaries to support what you
say. The graphs, mid.ps and final.ps,
are graphical summaries for mid and final, respectively.
Background
The following is a sample section based on
http://www.am.ndhu.edu.tw/~chtsao/edu/r4you/r01.html
You are referred to the page for detail info.
The data set, data2.txt, is a fake data set for midterm
and final scores for a famous National University in
Eastern Taiwan. The name is withheld for confidentiality. :)
R Output
> t<-matrix(scan("data2.txt"),ncol=2,byrow=T)
Read 22 items
>
> # The data has 2 columns and read by row
>
> exam <-data.frame(mid=t[,1],final=t[,2])
> t
[,1] [,2]
[1,] 33 45
[2,] 23 34
[3,] 12 67
[4,] 21 99
[5,] 32 98
[6,] 99 23
[7,] 23 78
[8,] 78 32
[9,] 43 12
[10,] 44 55
[11,] 34 23
> exam
mid final
1 33 45
2 23 34
3 12 67
4 21 99
5 32 98
6 99 23
7 23 78
8 78 32
9 43 12
10 44 55
11 34 23
> # Contrast the difference between "t" and "exam"
>
> attach(exam) # Use "exam" as our working dataset
> summary(exam)
mid
final
Min. :(1)
Min. :12.00
1st Qu.:23.00 1st Qu.:(2)
Median:(3)
Median :45.00
Mean :40.18 Mean :(4)
3rd Qu.:(5)
3rd Qu.:72.50
Max. :99.00 Max.
:99.00
> mean(exam)
mid final
40.18182 51.45455
> var(exam);
mid final
mid 682.1636 -417.1909
final -417.1909 928.6727
> stem(mid);stem(final)
The decimal point is 1 digit(s) to the right of the |
0 | 2
2 | 133234
4 | 34
6 | 8
8 | 9
The decimal point is 1 digit(s) to the right of the |
0 | 2
2 | 3324
4 | 55
6 | 78
8 | 89
> par(mfrow=c(2,2)); # Setup the graphical device
> # I use "mid" as the variable, you can try the command on "final"
> hist(mid); boxplot(mid); qqnorm(mid);
> plot(density(mid));
> stem(mid);
The decimal point is 1 digit(s) to the right of the |
0 | 2
2 | 133234
4 | 34
6 | 8
8 | 9
> detach(exam) # Let go exam.