Exercise 1 on correlation

 

In a study one compared two instruments for measuring the peak expiratory flow. For a sample of 8 person, one measurement was taken with a high quality instrument (called "pef" below) and one measurement was taken with a cheaper instrument that people with asthma may have at home (called "minipef" below).

 

The results are given in the table (in liter per minute)

 

Person	1	2	3	4	5	6	7	8
pef	494	395	516	434	476	413	442	433
minipef	512	430	520	428	500	364	380	445

 

 

a) Read the data into R and make a plot of the data. What can you see from the plot? (See the introduction to R or ask the instructors if you do not remember how to read the data into R and/or make a scatter plot of them.)

 

b) Compute the correlation between "minipef" and "pef". (See slide 11 from the lectures for R help.)

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c) Find a 95% confidence interval for the correlation. (See slide 13 from the lectures for R help.)

 

d) A person uses the cheaper instrument to measure the peak expiratory flow and records the value 475 l/min. What is your prediction of his/her value measured with the high quality instrument? (See slide 18 from the lectures for R help.)