Statistics - Calculating Variance

[samisazerahga]

@tremerrion6 that is what i want to know

[JAYMARINE1982]

Great job thank you very helpfull.

[cfrank028]

So helpful. I have an Exam tomorrow, and I am so glad you explained it so clearly! The book does nothing for me.

[eviliname1]

very helpful thanks :)

[reinar17]

i like the way you teach, very clear, comprehensive, let me take that and serve as my ultimate and reliable source for my school task in com math. thank you so much

[cherry3211]

THANK YOU! VERY HELPFUL!

[TheHIV123]

This is wonderful, thanks very much.

[hardcoremetroid158]

@yanivdar it is just n if it is the entire population or everything possibly involved, when it is saying n-1 that means it is a sample not the entire group

[yanivdar]

my teacher gave me the formula without n-1...just n. Which one is correct?

[ralphplaza1]

Fantastic!!! Thank you!! Was able to follow up the steps.  Thank You!!!

[odomaa1]

This was actually good! fully understand variance now!

[lovelypoop123]

Is it fair to say that the variance at the end is squareoot(4.5) ?

[dandiaz19934]

you probably just saved me passing my remedial math class. gassho!

[Madkidfox]

Fantastic stuff..

[pjfs80]

Thanks, very clear steps. Do you think you could expand this to 2 variables and discuss the covariance? Cheers Jon?

[MoN1T0r]

Thank you so much. You taught me in 05:07 what my teacher couldn't in 1:20:00. The only tip I can give you is when you are doing youtube video to be a bit more legible. At 2:30 I can't read what is next to "i"

[GohansRiceBall]

@MoN1T0r It is a part of the summation i = 1 to n (1 is next to i and the n is on top of the sigma)

[130797ONI]

thank you, but one question, isnt s2, the estimated variance? are their differences in caluculating them?

[pander2285]

Thankyou so much!! I was just missing one step and you really helped clear things up

[Entreri1887]

Thanks a bunch! This was quite helpful :)

[9018393]

thanks



[jman12348]

saved my ass for my ecology test! why cant professors break it down like this. You ask them for an example and they just solve it in front of you and then stare at you waiting for approval.

[mqgTWO96]

Is this population standard deviation or sample standard deviation?

[Poochalot]

Thank you, I couldn't figure out how the variance was 14, after this I finally had a 14 :)

[Koni804]

helpful I took 3 month from JC and I total forgot some stuff on stat. thanks for postin

[deejaydan1]

14 people failed statistics and blamed this video

[TEAMFISHLESS]

this is amazing

[darfurnub]

I would have failed my statistics exam without this haha

[collingcollege]

very helpful! thanks so much!

[TheIkitta]

Excellent! I also appreciate the comment about n-1 because all other websites use n.

[Spacewolf78]

So is the formula the same for both population and samples?

[stlhockey18]

@Spacewolf78 i would also like to know the same question

[patrickJMT]

@tremerrion6 you use n-1 when taking a sample and you do not have the entire population. i forget the mathematical justification, but it makes the estimate more accurate.

[AnUnlimitedRecord]

@patrickJMT degrees of freedom.

[mygrinningsoul]

OMFG!! thank you so much seriously...taking Stats this semester and I was totally stumped...thanx much....was very helpful and now I get it...sweeeeet...

[fireflymkz76]

thank you so much for breaking it down for me!!

[themadrfucker]

I can't explain how thankful I am to you, i'm going into the 11th rade and i'm taking the IB Higher level math course and for that i need to study 7 chapters of math work on my own over the summer. Without your help I wouldn't be able to do it :D

[animelovergal2002]

I always saw the funny shaped E sign in all my Math Books (pages with formulas in the back or front), but no where in the book showed examples.

Then I was researching random Math courses on YOUTUBE and Google and came upon this video.

For a girl who hates math like me, I surely understood how to work problems like this out, thanks for the video.

I hope to see more from yyyyoooooouuuuu

[SJMcDevitt]

thanks for ur help!

[mss3331]

you are just generous man! thank you

[carballom1983]

I didnt understand this until I watched your video. Thanks!

[Obichrist]

need help please

on january 1 a savings account contains $1000. if no further deposits and withdrawals are made during the year, and intrest is earned at 5% compounded monthly.find the average amount of money in the savings account during the first 6 months(use logarithms)

[aoiaaon]

wow, now that wasn't so bad. i haven't open any math textbook or studied math for two years and am beginning to get confident at this one especially when it's on a video. i can pause and replay it however much i want to help me grasp concept. it's not so hard like i imagined. i think i will do well at this term's statistics class.

[trevboiii]

thank you thank you thank you v thank you thank you

[EXRazeBurn]

Thanks alot for a cogent presentation. All too often my professors assume we know certain steps and "jump ahead" during solution explanations in order to cover as much material as possible in their lecture hour, leaving some of us in the lurch. It's presentations like this that help fill in the gaps.

I do have two points through, one relavent, one not so much. In my class, they said rather distinctly this formula used "n" as the denomenator, not "n-1", thoughts?

Two, southpaws are awesome!

[chefshitpiece]

@EXRazeBurn Theres a reason your proffessors do that...its to weed out the freaky smart students from the average. Im not one of the freaky smart kids...but Im smart enought to know what the profs are up to...sneaks looking for freaks! Learn everything in the course before you sign up, anything else is academic suicide, trust me on that one. They arent there to teach, they are there to find the next Einsteins...and your tuition pays for the whole fracking thing!

[tenseman08]

standard deviation =sqrt (Ex^2/n - (Ex/n)^2 ) ....much easier formula

[zippy1006]

we have end of course tests and since i was in accelerated... the bad part is that we learn math 2 like the year before but still learn some of it this year. And SO much information is lost. and i think i bombed my test. nbd or anything. Mostly because the questions dealt with standard deviation. and so i was surfing through the web and when i looked for math help, the only thing i searched for was: patrickJMT. haha thanks so much!

[evwijlemans]

the use of n-1 is especially important when it concerns a low number of samples. If there are a lot of samples the difference is negligible. however, if it concerns a small number of samples it does. This is best illustrated in the example of just 1 sample. If you would just use n, you would always find s square = 0, which is of course nonsense because with 1 sample there is no variance.  n-1 is used because in that case you would be deviding 0 by 0, which is an incalculable quantity.

[Doonsebury1]

Thanks man, i was stuck on this!!

[TheRulaBaby]

thanks a lot buddy!!

[theeba80]

thx alot bro

[SneakyPete1991]

Really helpful, thanks!

[lalacoolgirls]

Thank you for the guidance.. There was a slight problem though.. I have an assignment and it has to be done by using the excel sheet and microsoft word.. I used your technique to do it on the word format and the end result differs from the "Excel" sheet... I then tried the dividend as ( N) and not (N-1) and it conquers to the answer on the excel sheet. I still thank you for the easy steps.. You were much more helpful than my professor :o)

[Ev1lWaff3ls]

awesome video man. my professor didn't explain it very well but this was wonderful.

[tazmn23]

Good job. I got the right answer on the sample exam, so hopefully the same happens on the real exam.

[vticoupe7]

thanks

[suskabellaa]

OMG YES, THANK YOU! Jesus, it's so easy when someone actually explains the equation in English.

[ridethelight93]

can u please explain the last part what happended after 18/4 ?

[centurychallenger]

You help me understand easily. Now i know standard dev. - Malaysia

[preciouseyes87]

Thank you for this. It helped me a lot.

[SeXiLaDiK08]

You helped me way more than my teacher did. Thank you!

[mrssuperjwi]

Thank you! Thank you! Thank you!

[karthikaikumar]

Thank You

[PhilosophicalBum21]

Thank you very much for the variance lesson, good sir! I feel much more enlightened now. : )

[elbnderi]

U really helped me..

I'm a Saudi grad Engineering student at UW, Canada, and I'm taking a statistics course because I need it for my research, and I had no idea about variance. Since it's an advanced STAT course, I had to know such terms to follow up with the prof.

and thankfully, now I know what it means..

Thanks a lot..

[MissUnique685]

thanks very helpful!

[laaadddy]

thank you thank you.

short, simple and sweet.

got just what I needed out of it :)

[birdsofafeather1990]

I've read patilnikh's comment but I still don't understand why you divide by n-1 when the sample size is clearly n (5 in this case). Has it got something to do with the fact that if you have a sample size of 1 then it can't be done because there would be no variance?

[adschweinfurth1]

THANK YOU SO MUCH!!!!! helped me understand this for my class

[Mysticsam86]

REALLY good video :)

[m0onst9er]

Degrees of Freedom = n - 1

Explanation: (n) is the number of INDIVIDUAL data sets you have.

Question: So why n - 1?

Example: (from Keith Bauer)

You have the numbers 1, 2, and 3. These fall in List 1, the list that contains all your pieces of data collected.

1) Find the mean of the list. In this case, add 1+2+3 = 6 and divide that by 3.

2) Use that mean to take away value from each individual data. In this case, 1 - 2 = -1, then 2 - 2 = 0, then 3 - 2 = 1

2 - 2 = 0 is insignificant.

[sirina11]

wooooooooooooooooooooooooooooo­oooooooooooooooooo tuk tuk

[bayandsl]

all statistics are easy or not?

[SkiLlyLive]

SSSSSSSSSSSSSSSSSSSSSSSSSSSOOO­OOOOOOOOOOOOOO BORING jk but do you think doing this is fun???

[patrickJMT]

@SkiLlyLive yo yo yo g money, who the hell said it was fun?

[BlackdirtWarrior]

@patrickJMT Truth. A professor of mine once said, "If work was supposed to be fun, they'd call it something different."

[vi0lat0r84]

@patrickJMT LOL



[browno26]

@SkiLlyLive idiot

[LeBadman]

@SkiLlyLive It is fun yes.

[PiratesAndCowboys]

@SkiLlyLive People who are good at maths find it fun:)

[benbaker23]

VERY informational. Helped me a lot, in my 2nd year at a major university. Thank you.

[Tactickz]

Thank you for teachig me as I got my GCSES coming up, good help!!!!!!!!!!!!!!!!!

[1966zaim]

patric

thanks for a plus in calculus 2

im 45 yr old in my final year now

[patrickJMT]

@1966zaim good luck finishing things up!

[1966zaim]

my teacher seems incapacitated compared to you.

and thanks for a plus in calculus 2

[patilnikh]

No!!! What's the difference between VARIANCE and SAMPLE VARIANCE. On KhanAcademy he said just VARIANCE is divide by "n" and SAMPLE VARIANCE is "n-1"

[patrickJMT]

@patilnikh it is the difference between knowing exactly the population (maybe you take a poll or all 200 students in the 8th grade at your school) or you take a poll for the next election in your state (then you do not know exactly the population, you are just sampling). when calculating sample variance, it tends to give a better estimate when dividing by n-1,but i forget the reason why!

[patilnikh]

@patrickJMT Thanks! Though I did screw up the exam because for the difference between between confidence intervals, I directly subtracted the standard deviations.Though I got everything else, I did do something new. I got SIMPLE QUESTION right and all the HARD QUESTIONS RIGHT, yes, board exam!

[MissLexip00h]

@patrickJMT n-1 is the degree of freedom, assuming that it's not going to be the whole population. isn't that why?

[thechad005]

@patrickJMT

since it's a sample of data you just overcompensate for any error that may exist. It's just a heuristic

[ZappPSR]

Thank you very much for this video. I wish all math teacher could be so plain, simple and effective as you are, to explain things!! I give you an A.

[ThickSaucebaby]

this was really gooooood thanks alot been having some problems with stats esp this area thankssssssss

[Chaosbomber3]

you write pretty neat for a lefty :D

[TheSchnok]

If everyone took a stats course they wouldn't make all these annoying comments about how mad they are at the small percentage of people who "dislike" every youtube video. It seems like every video has at least 2. It's called the normal curve.

[birdsofafeather1990]

Many thanks for another brilliant video!

[swyzer]

Thank you SO MUCH for this video!

You just saved my day!!!

[nickreilly100]

I am starting my Statistics course next week, and all your videos will speed up my understanding of this course, you're a lifesaver. Big thank you and keep up the good work!

[lostismyconstent]

"(Variance) basically tells you, how far apart are your numbers"

THANK YOU!! I've been trying to figure out that all quarter and you just said in a sentence what two professors, a tutor and the rest of the internet couldn't explain to me in a month!

[darkprince200996]

you are great man that's help me so much i have an exam tomorrow in (medical community ) and they made us study maths & statistics that's annoing ...... so thank u so much

[71318elmo71318]

WIsh you were teaching at Deakin Australia, I've just learnt in 5 minutes what I've been struggling with for weeks. THANKYOU!

[renj3000]

great example thanks

[MultiSasha3]

wow!!, i spent 9hrs trying to understand this concept in class yet here i took 5minutes, the other 5minutes was to confirm if i really understood..., thanks sir

[Deathstar11978]

i just started this stuff after being out of education for 16 yrs. i walked out of a 2 hr lecture knowing nothing. You explain it perfectly in 5 minutes. thanks very much

[pasyk12]

So other than a "large" variance meaning a lot of dispersion and a "small" variance meaning little dispersion, what does the number mean to us. For instance, can I look at a variance of 4.5 for any hypothetical set of data and infer that the data only goes above/below the mean by about 4.5? or am I interpreting this wrong? Otherwise thanks for the vid!

[laneypeach]

THANK YOU!

[ExRussian86]

What's the point of variance, if variance is just an unsimplified version of standard deviation....???

[patrickJMT]

@ExRussian86 for sure they are both related (one is just the square root of the other). variance is simply a measure of how 'spread out ' your data is. it is just one other way to 'measure' the data so that one gets a bit more insight into the sample!

[OttoCarryUs]

Simple and effective, thank you Sir!

[robertcnd]

Great video U explain very very well... Im having a test in a couple of hours and you cleared any doubts thx!!!

[MusicFanatic1990]

You are so amazing for doing this. Thank you so much.

[qbanchick17]

amazing!!! thank u sooo much

[leadandflow]

Great explanation! Very clear and explaining every part of the formula! and which parts to work out first!

[MK519]

wow, thanks alot.. made it so much easier than the book

[caeb01]

you are awesome. saved me!

[caeb01]

you are awesome. saved me!

[westonworth]

n-1: My stats book says: when you find the population variance, divide by N, but for technical reasons, when you find the sample variance, divide by n-1.

[274933259]

u explained i better than in a math book. I thank you for this sir. Great vid

[patrickJMT]

@274933259 glad to help : )

[omina65]

You just saved the day !!!!!!!

thank you

[Brew608Crew]

Thank you for actually being clear about the subject and not changing the problem half-way through like other examples on here!

[lrstrader]

Thank you sooo much! My educational statistics teacher is a joke. You explained everything he didnt. Thanks!

[leudne26]

Wonderful, really didatic.

Thank you.

[MiZzDeeRoCkZ]

you have saved my life!!! thank you 

[Petecpa]

Very interesting

[sirleFavre]

Thaaaaaank Youuuuuuu!!!

[lizey1972]

Thanks so much for creating this video! I am taking an online statistics class and was having trouble with the variance formula. I found this video very precise and easy to understand! You saved me a LOT of trouble! Thanks again!

[lizey1972]

Thanks so much for creating this video! I am taking an online statistics class and was having trouble with the variance formula. I found this video very precise and easy to understand! You saved me a LOT of trouble! Thanks again!

[karimalhassan]

That's absolutly stupid, we do not subtract 1 from n in varinace formula, in fact we substract 2.

[hector06051]

you're awesome man. Keep the good work up. you a great tutor. : )

[smuhsin83]

Thank you very much for upload. I liked your explaining style, it was very simple. thanks again.

[ArmenianMafioz909]

You are the best. I like the way you are showing example..Math is my favorite subject...

[altamashansar]

Patric man u r genius xactly somebody rightly said why the hell we r paying bag loads of cash to idiotic teachers who cant even teach this simple variance u r MASTER.

[12963258741]

damn it!!!

.

.

"is that already that is like that already?"

.

.

i almost killed my self understanding my "what the heck is the language his using" professor and im glad you make me understand this!!

[alfatourist]

do you know the reaason why we subtract 1 from n in the variance formula?

[patrickJMT]

@alfatourist i used to know the mathematical reason, but have since forgot.

[patrickJMT]

@ba73da18lar302 your english is fine, so no worries : ) i would have to bust out a stats book (dont know if i even have any any more). if you have a decent book they should also explain it (hopefully!)

[ThisIsMe812]

@ba73da18lar302-- yey!!! i know the answer. N is for calculating population, while (n-1) is used for calculating the sample of a population.. hmm, is it clear?? =)

[yerimartinez]

@ba73da18lar302

From what I understand you subtract 1 from N when the variance of a sample. With a population it is only N.

[robertcnd]

@ba73da18lar302

I believe that when you dont substract the n-1 is becuase you are actually calculating the varicance for a population. When you calculate the variance of a population is the samw formula execpt you only divide by N

[ba73da18lar302]

@robertcnd yes.. But my comment is from months ago =s

I found the answer some minutes later :)

but thanks ^^

[NBAGOATS]

@patrickJMT YOU forgot something? Wow. You're a teaching genius. You should come out with a set of DVD lessons. I'm a total idiot and you cleared all this up for me.  Thanks!

[Martelo681]

@alfatourist The reason is theoretical. It can be proved that s^2 gives you on average the "true" value of the population variance, which is in principle what you want estimate. If you divide simply by n you underestimate the population variance. But using n instead of n-1 can also be justified

[OlleOutWar]

@alfatourist : because substracting 1 from the sample size is a better approximation of the (true) population variance

[mooch37]

It took my professor an hour to explain this whole process and you did it in 5 minutes and I understand everything now. Thanks man.

[patrickJMT]

@mooch37 tell your prof to show my video in class next time : ) he/she will appreciate that

[sharonhaidear]

Thanks dude ... Excellant work ....

[jacobbis4lovers]

I have to take this class for business. It doesn't seem as hard as Business Calculus, though.

[cindy09181980]

Thank you!

[STEPHENWRAYSFORD33]

I'm trying to learn a bit more about statistics in order to better understand R A Fisher's work on genetics and natural selection, thanks for uploading.

[avthemagnificent]

you dont know how much i adore youuuuuuu. THANKS BUDDY! (L)

[jeffanne143]

thanks so much to this video patrick!

my lessons are now clear to me!

i owe u one! ^^

-kayla

[haxor98]

This deserves so many more views. All your videos do :)

[jiminoc]

Very clear explanation.  Nice job

[navaikus]

Thank you very much ! you have saved my life before the exam ; ))

[AllOtherNamesTaken2]

What is the actual meaning of that 4.5? I haven't taken stats, so my idea of variance is the highest # minus the smallest, or maybe variance from the average. Why is the number 4.5 and not 5, 8-3?

[Tex259]

this is the guy who sits in the front of the room and pays attention. does the homework and studies tends to do pretty well. its nothing new to me.

[patrickJMT]

@Tex259 actually, i always tended to sit in the very back

[Yamsareverytasty]

@Tex259 fail :D This guy is a talented teacher thats what he is

[Tex259]

@Yamsareverytasty Could you teach me how you calculate for critical value?

[tmason122]

I'm doing a BSc degree at the moment and I'm in second year. Been taking a stats module this year and the guy taking it has no idea how to explain things like this to others. Thanks for the great video :)

[sam222ist]

Thank you so much!

[patrickJMT]

@bmhit1991 good luck!

[tong1111]

nice....

[laydeezman1]

this is VERY informative! I got stuck on a problem set was pulling my hair out and this helped ALOT im gonna send this to my friends who are also stuck!

Thanks for your time in creating this video man!

[rachnaka1]

thankyou soooo much something tht toke me days to undersyand toke just minutes with this video