# Dr. Dawn Wright

The Stats Files

## Single-sample z-test for the mean [7.4.30t]

Here is a common problem from intro stats: [7.4.30t] A random sample of 100 observations from a population with a standard deviation of 44 yielded a sample mean of 108. Test the null hypothesis that μ = 100 against the alternative that μ > 100 at an alpha of 0.05....

## Excel Simulation: Why is the Standard Error Equal to Sigma Divided by the Square Root of n?

Every time I teach the Central Limit Theorem, I get questions from students on why we divide the population standard deviation, sigma, by the square root of the sample size to calculate the standard deviation of the sampling distribution which we call the standard...

## “Easy” Excel Inverse Triangular Distribution for Monte Carlo Simulations Redux

Back in the dark ages when access to computers was not all that common, I was faced with developing a project schedule for, to me, a complex construction project. I was not that long out of school, so I sought out my boss with the hope he would give me some guidance...

## How to State the Conclusion of Your Hypothesis Test

The Easier Way After you have completed the statistical analysis and decided to reject or fail to reject the Null hypothesis, you need to state your conclusion about the claim. 1. To get the correct wording, you need to recall which hypothesis was the claim. If...

## Technology vs Tables and Rounding Mistakes

Joe, Two important points you bring up: Do not round intermediate values in a string of calculations. Wait until the very last step/answer to round to the number of decimals required by MyStatLab. On this problem and many others in this course, rounding too early can...

## Picking Alpha: The cost of Type I and Type II Errors

Earlier this year, I read of the analysis of the recent fatality caused by an Uber autonomous car in Arizona. (Lee, 2018) It occurred to me (and others) that this terrible situation is possibly related to Type I and Type II errors. (Efrati, 2018) A Type I is a false...