Uploaded May 2012 | Updated September 2026, 2 hours ago
I introduce inference procedures for the difference between two means in the case where the population standard deviations are known. I discuss the sampling distribution of the difference in the sample means, and discuss the confidence interval formula and the hypothesis test of the equality of population means.
The Cairo traffic police officer data is simulated data with the same summary statistics as found in:
Kamal, A., Eldamaty, S., and Faris, R. (1991). Blood level of Cairo traffic policemen. Science of the Total Environment, 105:165--170.
I introduce inference procedures for the difference between two means in the case where the population standard deviations are known. I discuss the sampling distribution of the difference in the sample means, and discuss the confidence interval formula and the hypothesis test of the equality of population means.
The Cairo traffic police officer data is simulated data with the same summary statistics as found in:
Kamal, A., Eldamaty, S., and Faris, R. (1991). Blood level of Cairo traffic policemen. Science of the Total Environment, 105:165--170.








![Confidence Intervals for One Mean: Sigma Not Known (t Method)
Introduction to confidence intervals for mu based on the t distribution. These methods are appropriate when we are sampling from a normally distributed population and the population standard deviation (sigma) is not known.
The cereal data used in this video is real data from a sample of 7 cereal boxes I purchased one day. The boxes had a stated weight of 750 grams. (Ive changed the story slightly in the video, but it is real data.)
For those that use R, below is the R code to find the values given in the video.
With 6 degrees of freedom, the t value with an area of 0.025 to the right (and thus an area of 0.975 to the left), can be found with:
qt(.975,6)
[1] 2.446912 Confidence Intervals for One Mean: Sigma Not Known (t Method)](https://i.ytimg.com/vi/bFefxSE5bmo/mqdefault.jpg)

