Sunday, November 12, 2017

(R) Confidence Interval of The Mean (T)

Below is an example which illustrates a statistical concept:

# A new machine is purchased by a pastry shop which will be utilized to fill the insides of various pastries. A test run is commissioned in which the following proportions of jelly are inserted into each pastry. We are tasked with finding the 90% confidence interval for the mean filling amount from this process. #

s <- c(.28,.25,.22,.20,.33,.20)

w <- sd(s) / sqrt(length(s))


[1] 0.02092314 

degrees <- length(s) - 1


 [1] 5 

t <- abs(qt(0.05, degrees))

[1] 2.015048 

m <- (t * w)


[1] 0.04216114

mean(s) + c(-m, m)

[1] 0.2045055 0.2888278 

# We can state, with 90% confidence, that the machine will insert into pastries proportions of filling between .205 and .289. In the above execise, a new concept is introduced in step 4. The abs() function, in conjunction with the qt() function, allows you to find Critical-T values through the utilization of R without having to refer to a textbook. A few examples as to how this function can be utilized are listed below. #

# T VALUES (Confidence / Degrees of Freedom ) #
abs(qt(0.25, 40)) # 75% confidence, 40 degrees of freedom, 1 sided (same as qt(0.75, 40)) #
abs(qt(0.01, 40)) # 99% confidence, 40 degrees of freedom, 1 sided (same as qt(0.99, 40)) #
abs(qt(0.01/2, 40)) # 99% confidence, 40 degrees of freedom, 2 sided #

I hope that you found this abbreviated article to be interesting and helpful. Until next time, I'll see you later Data Heads!

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