R notes for Activity 19-5: Sleeping Times
I will gather your sleep time data at the start of class and enter
them into a file. You can read them into a table with
SleepData = read.csv("/home/rebelsky/Stats115/Data/SleepData.csv")
SleepTimes = SleepData$HoursSlept
The second line allows us to refer to the vector as SleepTimes.
19-5 a: Graphical Displays
You should refer to activity 19-3
c for ideas of graphical displays.
19-5 b: Sample Statistics
You can get sample size, sample mean, and sample standard deviation
with
length(SleepTimes)
mean(SleepTimes)
sd(SleepTimes)
19.5 d: Confidence Interval
Since we have all of the original data, the easiest way to get
the confidence interval is to use the t.test
function.
You should substitute your own guess as to the mean hours
slept (in place of 6).
t.test(SleepTimes, mu=6, conf.level=.90)
Of course, you might also want to provide R with step-by-step instructions.
x_bar = mean(SleepTimes)
n = length(SleepTimes)
s = sd(SleepTimes)
t_star = qt(0.95, n-1)
ci_lower = x_bar - t_star*s/sqrt(n)
ci_upper = x_bar + t_star*s/sqrt(n)
c(ci_lower, ci_upper)
Rather than counting values by hand, you can get R to produce
a vector of the times in this interval with
NearMedian = SleepTimes[(SleepTimes > ci_lower) & (SleepTimes < ci_upper)]
length(NearMedian)
