Two-sample t test for difference of means | AP Statistics | Khan Academy
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- Опубликовано: 22 авг 2024
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Hypothesis test for the difference between means of two populations.
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why are you reading the comments. back to studying.
@@kriti5276 can u do both tho
Why did you click on answers?!
@@kriti5276 what a flex!!! 😎
@@vainca3192 what? Clicking on answers is what you are supposed to do as a highschool student 😎
@@vainca3192 then like what
tough for the donations they want, I really wish I could but most people watching are broke college students :( one day ill get you guys back if you're still around.
surely man! 👏
Yours is more comprehensive than the ones I av watched. Thank you
Two-Sample T-Test and CI
Sample N Mean StDev SE Mean
1 22 1.300 0.500 0.11
2 24 1.600 0.300 0.061
Difference = μ (1) - μ (2)
Estimate for difference: -0.300
95% CI for difference: (-0.550, -0.050)
T-Test of difference = 0 (vs ≠): T-Value = -2.44 P-Value = 0.020 DF = 33
One caveat I found out about pretty much all STAT tutorials and textbooks is that there is few real-life examples, especially business ones. It's either something like this that you can immediately put numbers into the formula, or something that is related to medical experiments. What I think that is really needed is how to APPLY that knowledge to a usual business question.
This is needed in some user research experiments, which is used to validate business hypothesis, e.g. in MVT or A/B testing. Two versions of a landing page / feature/ logo are tested on samples of users, and you want to compare how those two versions score in X property to keep the better one.
A helpful tutorial. However, I ran two different online t-tests with these mean, std and Ns, and both gave the same result which however is slightly different than the calculation here. They both gave a two-tailed p-value of 0.0165. Graphpad also gives the degrees of freedom, which was 44. That's pretty different than the estimated 22 (or 24?) here, maybe that is the reason. But the t-statistic was also a bit different, 2.4919.
I got the same value for the T statistic. I think he used exact values, that's why he's getting a different answer upon rounding.
I liked that you have used an uneven size for the two samples. Learned something new today xd
Felix Carpio is this the same thing as the welch’s t test?
When your University professor just links this video for online class instead of actually teaching it himself
I guess just looking at the mean versus the standard deviation you went with the unequal variance t-test. Otherwise we would have to conduct a F-test to determine if a pooled estimate could be used. I wish you mentioned something on this.
bruh if you know that much then why does it matter?
because I was confused and @steverensen2551 explained why I was confused, the comment was helpful@@DmanGaming
Hi, please may I ask what app are you using as for the calculator?
Interesting video, but you don't explain if you assume the variance are equal or NOT. You don't axplain if you use the welch method, or NOT. And your formula for the degree of freedom is curious.
True, watching the video left me with more questions than before I watched it.
I can say he is a very good artist please reply ☺️
Where we use pooled Estimate of standard deviance (Sp)
No, he doesn't use a pooled estimate, but he doesn't explain why.
Okay I understand the steps, But I don't understand some things like how do we determine the significance level? (Where did you get 0.05? out of thin air?)
from my understanding 0.05 is the default p-value for this sort of test. This represents 2 standard deviations (95% probability). However you could theoretically use any p-value.
is there a way to calculate the p value by hand without the calculator function? We are only allowed to use a very basic calculator that does not have tcdf in our exam. Thanks for the help!
so will i arrive at the same answer if i use the welch t test?
Degree of freedom = n1+n2 -2
I think so too
Thank you
i’m just trying to look for one that isn’t the conservative approach for the df because my teacher doesn’t use that🤦🏽♀️
1:26 Why are you talking about the alternative hypothesis after already having set the null-hypothesis? If that one is set, you don't have a choice anymore: It's just the complementary hypothesis that the null-hypothesis does not hold, so if you want to discuss the hypothesis, do so when you fix the first.
2:04 std dev of the sampling distribution of the differences of the sample means
Sir, what do I do if I want to test mean(A) > mean(B) ?
What type of calculation app was used?
based on the laws, why are you not pooling the variances
For a two samples t test if it is not given whether the population variances are not equal or not. Then which formula do I have to use to find degrees of freedom
There is a way to reject/accept the null hypothesis based only on confidence intervals instead of the p-value, right?
Yes
KAITO MOMOTA LUMINARY OF THE STARS 🌟 ‼️ is growing tomato plants atm
How do you calculate the minimum sample size you need to compare 2 sets of data?
I have data of two rivers. River a and river b. The data is of before and after the application of the chemical. One sample set is bigger than the other.
I need to know in which sample the chemical was more successful in removing parasite than the other.
Which test should i use. ? Please please please guide
Thank you! Super helpful! A quick question: why is the df = min(sample size)-1 ?
Good question.
Though you have two samples, you are comparing their means. Therefore, this is a single variable analysis and degrees of freedom is n - 1.
Now recall that a chain is only as strong as its weakest link, a group of runners that must run as a group is only as fast as its slowest runner, and a statistical test is only as strong as its weakest test. In statistics, more data is better. Therefore, you must adopt the lower of the two values as your basis for degrees of freedom.
I got a question, what if the two sample number is very different?
ex:
N1 = 24
N2 = 2500
the DF still min(sample size)-1, in this case, DF = 24-1 = 23 ?
I checked wiki, it should be N1 -1+ N2 -1 for the independent two sample test
what is the equation for p-value calculation? (can this be done in excel?), thanks
for calculating p-value in excel with t-value known ...you can use the function T.DIST(tvalue, n-1, TRUE). this will give the p-value for left tailed test. for right tailled test, you can subtract this value from 1. similarly for two tailed test, use 2* the pvalue obtained by using the function.
What app did u use in solving the p-value?
As sample size are large so I should use z test????
Yes And must n1=n2
Yes if the sample size in above 30, you should use z test
So i should use z test? Since my sample size is 102
Doesn't the test statistic and degrees of freedom depend on whether variance is known or unknown? And then there are two more approaches if unknown, assume variances equal, assume variances not equal
Please look at the below solution and confirm for difference in P-value:
Difference = μ (1) - μ (2)
Estimate for difference: -0.300
95% CI for difference: (-0.550, -0.050)
T-Test of difference = 0 (vs ≠): T-Value = -2.44 P-Value = 0.020 DF = 33
Can you please ellaborate on DF?
Is there an online calculator like the one he is using?
best statistic calculator online
You will just encode the values then it will give you answers
Why you use t test? The summ of the sample wize is greater than 30/ n>30, you should use z-test instead 9f t test
What if I calculate the t value as XB-XA. Will that make difference in conclusion
Hi, are you not going to take the absolute value of the differences of the two means (numerator)?
degree of freedom = n1+n2 -2 = 22+24 -2 = 44 , Please reply why it is 21 ?
i also doubted that.
I think the df should be 44, am I wrong?
Where can I get the TI-84 Plus CE in software? Thanks
One way ANOVA test: between groups sum aquare = 66636.83; df= 2; mean square%=33318.41; f= 11.710 and sig=.000. Within groups = 189577.87; df=669; mean square= 283.37 what is the answer?
so basically you are assuming that the groups variances are not equal right ?
There is no assumption. It is stated that the two have different standard deviations.
@@aurangzebrathore5001 that doesnt mean that the population standard deviations are different. There are two different tests that can be used to test if the population means are different. One test is for when the population variances are different and one when they are the same. In this instance Dr. Khan is using the method for when the population variances are different.
thats like saying the population means are different because the sample means are stated as different
very nice video
My question is how did you get the value for X1 and X2, S1 and S2. I'm using data from fresh sample
If we find significant by applying t statistic between two groups ,then how do we decide that the significant difference is recorded in which group as compared other group?
god bless you sal
Thank brother you made it easy
So this is like a shortcut?
what if the sample is equal?
You use a pooled t-test I am pretty sure
what if the number of sample is bigger than 30 (large sample)? should i still using this formula?
lack the assumption that the height follows normal distribution to apply CLT?
I think you forgot polled variance
why am i getting -1.7875 for 't'
thanks vulcano
One way Anova test
Well, these tomato plants taken are just samples instead of original populations. So should the variance s^2A and s^2B used be the unbiased estimators instead of variance of the samples?
My two sample t-statistic is -3.02
What is my p-value?
If you are still interested to find the value of p you need the degree of freedom too. As in the video was specified it is the lowest size of the two samples -1. And finally to calculate the value you can use matlab function tcdf(t, df). df - degree of freedom
Can i used t-test when my sample is 100?
Please answer me😭
No. You'll use Z test as T-test is used when sample size is usually under 30
nice
Mistake
0.3^2=0.9
.3 *.3 is 0.09 I believe its your mistake.
My two sample t statistic is -7.14
Can someone tell me what is the p-value?
I also need the degree of freedom
What if the two samples are the same?
nothing change, I guess...
In t dist we use Sp and we cant use the standard division S ?🤔🤔
me too
Is the two sample t test the same as the student t test?
According to my statistics book, t-Test has 1 sample. The 2 sample test is called Pooled-t or non-pooled, depending on the sample size or standard deviation.
Why did you calculate 0.9 and not 0.09?
0.3 the whole square is 0.9 tata y he calculated mistakenly he wrote as 0.09 dude
0.3^2=0.09 this is not mistakenly calculated.
Okay... what's your point?
To teach statistics learners how to apply a t-distribution to a difference of means problem
Sweety
is this a two sample paired t test?
Yes, it says it in the title of the video
First!
.
2:58- When you square 0.3 equals 0.9 not 0.09.
.3^2 = .09
He’s not wrong
Squaring a number which is less than 1 makes that number smaller, not bigger.
I really have never liked this guys voice