That’s a nice way of thinking about it.

-Ryne

]]>Consider this: you draw two large samples (Group A and Group B) from the same population 100 times and calculate the 95% CI for the mean difference in weight between groups. The most impressive difference showed that Group A weigh – on average – 4.4 more kg than Group B, 95CI % 2.2-6.6.

Do you think it is legitimate to conclude that there is a 95% probability that the interval contains the true mean difference? Obviously the answer is no.

Frequentist statistics (according to Neyman/Pearson school) do not allow us to say anything whether a particular finding is true or “confident”, rather it tells us something about what we can expect from the procedure: in the long run.

Best regards,

Steve

If I were to run the experiment 100 times, I’d get 100 slightly different confidence intervals.

If they are 95% confidence intervals, then 95 out of those 100 CIs would contain the true mean. Or, conversely, 5 of those CIs would NOT contain the true mean. The indivdual CIs either have the true mean or not. There is no probability for an individual CI.

So a 95% CI is erroneous 5% of the time.

]]>I read lots of paper for Confidence interval. I understood the theory behind that, but I have one practical problem.

If I have 95% confidence interval of mean weight of one school (55kg-75kg) of 240 students. Now please let me know what should I interpret with respect to (55kg-75kg). Total school students are 3500.

Thanks

Hitesh ]]>

I found the original blog and found the link you provided there to this site. I didn’t really want to waste my time looking at this for my classes, but figured it would be a good chance to get into R a little bit more.

Anyhow, I have one online course where I was suspicious of some cheating. The students are taking the test on their honor not to work together. I thought probably a good majority of students are honorable, and I think that’s still the case. But I had a good number of student falling on the perfect match line for the first exam I’ve looked at. Not cool! When I dug into other aspects of their tests, my worries were confirmed (they took the exam at the same time and even had the same wrong choice on the wrong answer). I’ll be presenting this to my chair or dean to see what they want to do with it.

In my other large class that meets in person and has well proctor exams I only saw one problem on the one exam I checked (and I had been suspicious of this student from before – he failed anyway so I’m not too concerned).

Thanks for posting your more detailed analysis. I have not tried it yet, but I may have to if I need to convince people more rigorously of the problem.

]]>I just now looked the article up in Google Scholar, and it looks like there has been a reasonable amount of work since then.

If I get a chance, I’ll edit out identifying information, and send you the report I wrote. I

]]>It’s a shame that people cheat and make us worry about them. I hope talking more about it will have some deterrent effect.

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