Pooled-Variance t Tests and Confidence Intervals: Introduction

The shame/young offender data is simulated data with the same summary statistics as found in:

Owen, T., Fox, S. (2011). Experiences of shame and empathy in violent and non-violent young offenders. The Journal of Forensic Psychiatry & Psychology, 22(4):551-563.

[brittneymanzagol]

I'm so grateful there are people like you who will take the time to put such useful videos on Youtube

[MrMoapy]

I'm not sure if you're still checking comments - but I just wanted to say that your videos are amazing and (statistically significantly) much easier to understand than the course content for the Uni Stats course I'm doing. Thanks to you I feel confident in my final exam!

[Explorer]

Who on earth downvotes this ? So many stats students would be lost without this guy !

[EvilSapphireR]

It goes without saying these videos are incredibly awesome! It would've been cherry on top if the concept of confidence interval was intuitively connected with the hypothesis testing somehow. For example the video mentions we can say with an (1-α)*100% probability that the difference (μ1-μ2) lies within the range tα±SE(x1bar-x2bar) from any obtained value of (x1bar-x2bar). Which made me think the hypothesis testing would go something like the probability of finding zero within this tα±SE(x1bar-x2bar) range, which would mean the two population means were the same. But instead it doesn't expand on the point of confidence interval anymore and goes to regular method of P value calculation. Amazing content regardless!

[pandabeargogo]

+jbstatistics I need to determine whether there's a significant difference between 2 sample's variance. They are both the same size from the same population. Does the information in this video relate to my task? I'm finding myself getting very lost between what's in this video, F-test and chi^2 test, to produce my test.

[christineabu]

You are simply an angel! Thank you very much for the excellent job.

[prasannakannan]

Wow!! such clear explanation. Terminologies are so accurate. All your videos are awesome. Thanks a ton. I would love to see a video from you explaining Bessel correction and degrees of freedom. is there one already?

[Exoduse]

Hi, is the pooled-variance t procedure the same as the student's t test? Also, as mentioned early in the video, there are 3 assumptions to the pooled-variance t procedure but I want to ask how to actually determine whether the data to be analyzed hold these assumptions.For the first assumption of independence, do I use a test for auto correlation on the dependent variable values? For the second assumption, how large is large? n=500? n=20? also is there a calculation or rule of thumb for this? For the third assumption, I feel that assuming equal variances can unrealistic, and may cause unfavorable results in some cases. Is there a guideline as to when to use unpooled variances or the Welch test that you mentioned earlier?

Thank you very much!
P.S. I often have a hard time learning statistics all because of all the abstraction present in mathematics. I am often worried that the results that I obtain from an analysis may not be accurate--which kind of defeats the purpose of performing a statistical analysis.

[whatyouwantyouare]

I think at 4:30 you meant to say "variance" not "mean" ... should be "lost one degree of freedom when we estimated each *variance* " ... right?

[huanghouWuZetian]

the second assumption is not that important for large samples. but shouldn't we use a test based on normal distribution for large samples ? t-test is for small samples

[Gondee]

What do you use for the alpha to search for in the T table? Especially if there is no alpha given

[eliyalee]

Why couldn't you be my stat professor...

[matthewjames]

Shame, shame, shame! Oh wait this isn't a game of thrones scene...