Question

In​ statistics, what does df​ denote? If a simple random sample of 22 speeds of cars on California Highway 405 is to be used to test the claim that the sample values are from a population with a mean greater than the posted speed limit of 65​ mi/h, what is the specific value of​ df?

Answer 1

df refers to degrees of freedom.

the specific value of​ df in the example is 21.

Explanation:

In statistics, degrees of freedom is the number of values in the final calculation of a statistic that are free to vary. It is the number of independent ways by which a dynamic system can move, without violating any constraint imposed on it.

In other words, degrees of freedom is the number of independent pieces of information that went into calculating the estimate, and calculated by

n – 1 where “n” is the number of items in your set.

In the question, a simple random sample of 22 speeds of cars on California Highway 405 is to be used to test the claim, thus the number of items in the survey are 22.

From this we get:

df=22-1=21