T-Test pre conditions

Okay, I am taking an introductory course in statistics about Nevin Manimala and we are learning about hypothesis testing and student’s t-test.

As a part of an assignment, I am supposed to verify whether t-test requires:

  1. Homogenity of variance
  2. Normal population
  3. independence of data

How do I go about verifying these requirements experimentally?

submitted by Nevin Manimala Nevin Manimala /u/97amarnathk
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Question working with large data set, assessing accuracy:

Trying to do some simple data analysis with respect to credit card fraud detection. I was wondering what experts consider when trying to assess accuracy with highly unbalanced data set.

The data set I am looking at has over 284k observations however < 0.2% are fraudulent.

submitted by Nevin Manimala Nevin Manimala /u/omgouda
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Penn State vs Texas A&M for online MS degree.

Got accepted to both. Which should I attend?

I currently work in food manufacturing in quality control, but I am interested in working in the energy sector. I’m mainly interested in optimization of production processes and formulations of products if my interests have any relevance.

My background is a dual BS in chemistry and biology. I got a minor in mathematics with an emphasis in modeling. I am familiar with C and have some superficial knowledge with C++.

Pros and Cons I see: Texas A&M is significantly cheaper (my work will pay for about a third of it to 75%, depending on the credits I take in each semester). Penn State is six credits shorter than A&M and no qualifying exam to stress over. Texas A&M seems to have a larger variety of courses to study. Penn State doesn’t appear to make you focus on SAS like A&M does. I’m interested in learning R. My current work doesn’t care what you use. But I can’t predict what future companies will want.

Any pro tips for me?

submitted by Nevin Manimala Nevin Manimala /u/TwigsthePnoDude
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Dealer returned my car with a blown engine, in need of advice.

Alright so this all happened yesterday at a dealer in NJ. They will remain nameless as I haven’t yet heard what they are proposing going forward. The vehicle is a 2013 VW GTI 6MT with 111,000 miles on it. I have always performed the scheduled maintenance on time or a bit early, oil/filter changes <5000 miles. Stock engine, no tune.

I brought the vehicle to a dealer yesterday to have the manual trans fluid changed. VW specifies ‘lifetime’ fluid, but I don’t buy it. A buddy of mine drove his GTI past 170,000 miles with no trans issues after doing a change at 100k, so I figured why not do it. The car has given me no major issues and was running strong when I delivered it.

When I got to the dealer I had them quote spark plugs because I’ll be due in ~9000 miles. They came back with ~$350 so I just said I’ll do it on my own. The plugs are something like $12 a piece. This is relevant because they had included both jobs on the invoice and crossed out the spark plugs because I elected not to do them.

They brought the car out about an hour later, I paid, then off I go. Before I get out of their parking lot I notice a weird ticking noise that’s timed with engine speed. I look down and the check engine light is flashing. I turn around and bring it right back in.

The service advisor comes back half an hour later and says there are misfires on cylinders 3 and 4 and zero compression in both cylinders. Fuck. They say it likely needs a new engine. Double fuck. I call bullshit and tell them the car was working fine when I delivered it to them, they’ve returned a broken car. They need to fix it. I go out and review my dashcam footage and don’t see any abuse of the car – in fact they never even road tested it.

I sat down with the service advisor and he says nothing they did could have caused this issue, it’s likely the timing chain tensioner, he’ll see what VWoA can do for me. I get a loaner from them and tell him to figure out exactly what is wrong with the car. He calls later on and says cylinder 4 has a broken valve spring and he will see if VWoA will help replacing the head.

I’m at a bit of a loss here – it seems super unlikely that THE ONE TIME I bring the car in for service, there is a major engine failure. This just doesn’t smell right. I’ve never heard of a valve spring failing on these cars. I’m not ready to part ways with it – I’ve spent a lot of time and money customizing it to make it the perfect car for me.

I wanted to get any outside thoughts on what could have caused this, or what I should do now. I’m expecting cost of repair to be >3k. I can’t think of any reason why the failure could be something caused by the dealer, except maybe the spark plugs? If they’d started the job and failed to re-install correctly, it could perhaps be related?

submitted by Nevin Manimala Nevin Manimala /u/CallMeMrMindfuck
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Have 1,000 miles left on a Subaru bumper to bumper warranty.

I just purchased a 2016 subaru WRX premium from a dealer and they informed me I just have under a 1000 miles left on the original subaru 36000 mile warranty. Would it be prudent to take the car into a subaru dealership to get anything fixed before the warranty expires and what exactly should I look for to get replaced/checked? Would it be hard as a second owner to get warranty work? I don’t see anything big wrong with the vehicle but I have only had it for a day and have never owned a subaru.

submitted by Nevin Manimala Nevin Manimala /u/cheeseman52
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Modelers age 40+ in a corporate setting

My question is what happens to modelers who work in industry as they get older. From my experience when I’ve seen my boss one or two levels up, some of them haven’t done a regression in at least 10 years and I truly don’t even respect their intelligence on pure stats and modelling. I doubt they’ve read a stats book in at least 20 years. Everyone at work sits in a cubicle or open desk seating and nobody even has books, nobody spends work time reading. It would look really weird if you did. Some of my bosses have told me comments like “in my previous life when I did all this text book models” … but how/why did they move away from that??? It seems this happens to everyone. I don’t understand what they do all day, yet now I fear I am coming to that same cross road as a mid 30 something modeler. I think they get bogged down in the business details and business functions, and use that knowledge to steer the modeling efforts of others. I used to not care at all about the business specifics, I always thought knowing the academic details was the hard part, picking up the business info as needed would be easy.

But now I find I have a real lack of knowledge about the business, and with my fixed time limit at work (plus what I do outside of work) I just can’t keep up with both. I can devote my time to learning more about the business, I can devote my time to not forgetting a base core of stats knowledge, or I can devote my time to learning more about stats. Pick 2. I’ve just come to accept that I can’t compete with a 25 yo who just finished grad school, they will run me over in technical knowledge. The time it takes for me to even work through an old linear algebra book is a matter of weeks, and that’s just to not forget stuff, let alone learn new stuff. And that takes away time I could spend learning more about the industry. There is just no way I can compete on technical knowledge, and that will only get worse as each year by year goes by. However, the college grads know nothing about the business, so I guess that is supposed to be the material I should focus on? I have seen all kinds of problematic modelling efforts and mistakes that show a mis-understanding of general business knowledge. I feel like I should just give up on my hope of staying sharp with textbook stats knowledge. But it feels kind of sad to give that up.

Anyone else face this before?

submitted by Nevin Manimala Nevin Manimala /u/cooked23
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