Question

We wish to test if SBP

changed after treatment for subjects in the treatment arm. Test

H

0

:

μ

t

=

μ

c

versus

H

a

:

μ

t

6

=

μ

c

for patients in the treatment arm using R

function

t.test

.

44. What is the mean change in SBP (pre - post) in the treatment

group?

– a)

-4.230

– b)

2.212

– c)

0.543

– d)

-0.654

45. What is the 95% confidence interval for the mean change?

– a)

(-3.2543, 4.2543)

– b)

(-7.5445, -1.4325)

– c)

(2.5436, 9.3654)

– d)

(1.4329, 2.9911)

46. What is the

t

statistic for the test?

– a)

-2.5436

– b)

2.5436

9

– c)

5.8595

– d)

-0.4365

47. What are the degrees of freedom of the test statistic?

– a)

48

– b)

50

– c)

24

– d)

25

48. What is the

p

value for the test?

– a)

0.3825

– b)

≈

0

– c)

0.0133

– d)

0.9483

sex	arm	sbp.pre	dbp.pre	sbp.post	dbp.post
m	t	123.1	84.2	120.2	82.3
m	t	115.4	93.1	114.2	92.1
m	t	110.2	86.8	109.2	96.6
m	t	118.4	93.2	117.7	98
m	t	119.3	91	114.1	94.6
m	t	119	91.4	118.8	83.2
m	t	116.9	80	116.1	70.5
m	t	122.3	87.3	117.9	87.4
m	t	125.1	99.6	120.9	99.9
m	t	124.2	83	121.1	87.6
m	t	120.8	90.3	117.4	99.9
m	t	121	87.5	124.2	82.4
m	t	112.8	88.7	109.8	90.3
m	t	117.8	93.1	115.9	95.9
m	t	112.2	82.3	112.1	80.7
m	c	125	86.3	125.4	82.6
m	c	124.3	92.3	125.5	86.8
m	c	123.5	89	123.6	84.4
m	c	128	97.4	130	94.3
m	c	125.7	97.6	126.6	91
m	c	122.8	96	124.3	92.4
m	c	117	85.3	115.4	88.1
m	c	128	87	126.6	87.6
m	c	119.3	83.1	116	82.4
m	c	123.3	100	123.9	97.5
m	c	124.5	90.7	124.2	98.3
m	c	120.7	94.5	123.8	103.3
f	t	112	81.9	111.1	85.5
f	t	122.2	89.8	121.6	89.3
f	t	119.5	90.3	115.2	91.3
f	t	108.7	90	105.8	100.7
f	t	121.9	97.9	118.3	101.3
f	t	118	80.1	117.4	75.5
f	t	120.4	88.4	117.1	92.3
f	t	115.7	92.1	111.6	93.2
f	t	117	97.8	114.1	96.1
f	t	119.1	94	115.9	88.4
f	c	106.1	90.6	107.5	87
f	c	109.6	83.5	107.2	85.2
f	c	111.9	88.6	108	90.7
f	c	115	87.3	117.1	80.5
f	c	115.3	91.6	114.8	91.1
f	c	124.4	92.5	123.3	96.7
f	c	115.5	85.5	119.7	77
f	c	119.6	99.6	117.4	105.5
f	c	108.3	92.1	110.4	87.8
f	c	115.1	89.1	116.1	95.4
f	c	122.3	87.7	121.2	92.1
f	c	113.1	85.3	113.2	92.1
f	c	120.5	96.4	117.6	90.6

Answer 1

I am saving the data file in excel with name 'data' on my desktop.

Use following command to import the data into R-

> library(readxl)
> data <- read_excel("C:/Users/username/Desktop/data.xlsx")

--------------------------------------------

Once, you have the data in R, you use the following codes for each part-

44)

Use the code -

> mean(data$sbp.pre[data$arm=="t"]-data$sbp.post[data$arm=="t"])

This will give you the output -

[1] 2.212

Which means option (B) is correct.

-----------------------------------------------

45)

Use the code -

> t.test(data$sbp.pre[data$arm=="t"],data$sbp.post[data$arm=="t"], conf.level = 0.95, paired = TRUE)

The output we get is-

This should give you the required confidence interval as-

95 percent confidence interval:
(1.432866, 2.991134)

So, option (d) is correct.

----------------------------------------------------

46)

For the same code in previous part, you get the test statistic = 5.8595

So, option (c) is correct.

------------------------------------------

47)

Again, degree of freedom = df = 24. (obtained from the same output)

So, option (c) is correct.

--------------------------------------------

48)

The p-value from the output = 4.818 x 10^-6

So, option (b) is correct.