[Blindmath] Statistics help

Wed Sep 21 06:28:40 UTC 2016

Sabra,

I used "R" not "are" to get the numeric answers. The commands were on the lines before the number signs.

To find the median, find the group that is the one whose cdf first exceeds 0.5. The cdf is found by finding the cumulative sum of the probabilities of group membership. If you are given counts then find the probabilities by dividing counts by the grand total.

I think these are questions that you ought to be asking your course staff when you need assistance. If camping outside the lecturer's door isn't going to work, then ask which of the department tutors is going to help you.

As a postgrad student, I earned much of my income from doing tutorials, most of which were intentionally not organized; that is, the work I did was totally driven by student need, not lecturer agenda. I spent hours answering questions like yours.

None of the questions you've asked today require vision, although transfer of the course material might be a blindness issue. I've seen plenty of resources that would answer your questions on the web, but it's been easier to just answer them than go  looking for a decent resource.

Can I suggest that you point your lecturer towards the article Theodor Loots and I wrote on teaching statistics to blind students. The bibtex style reference is:
@article{GodfreyLoots-JSE,
author={A. Jonathan R. Godfrey and M. Theodor Loots},
title={Advice from blind teachers on  how to teach statistics to blind students},
year={2015},
journal={Journal of Statistics Education},
month=Nov,
volume=23,
number=3,
url={http://www.amstat.org/publications/jse/v23n3/godfrey.pdf},
pages={1-28}
}

And inform them that they are welcome to contact me if they want to know more. When you do send these details to your lecturer, please copy me in on the thread.

Jonathan

-----Original Message-----
From: Blindmath [mailto:blindmath-bounces at nfbnet.org] On Behalf Of Sabra Ewing via Blindmath
Sent: Wednesday, 21 September 2016 5:21 p.m.
To: Blind Math list for those interested in mathematics
Cc: Sabra Ewing
Subject: Re: [Blindmath] Statistics help

Thanks. I can't find where you used are. I see some spots where there are blank number signs though. Is that where I would use a number from the normal table? Also, what is the formula for finding the median for grouped data using a frequency table? I found it on lots of websites, but it is a picture. I also asked one of my classmates to write it for me, and it was still a picture.

Sabra Ewing

> On Sep 20, 2016, at 9:43 PM, Godfrey, Jonathan via Blindmath <blindmath at nfbnet.org> wrote:
> 
> Two questions.
> 
> Neither uses the empirical rules; both use the standard normal tables.
> 
> P(116<X<120)
> =P(X<120)-P(X<116)
> =P(Z<(116-118.5)/1.2) - P(Z<(120-118.5)/1.2) Sorry, no tables in this 
> office. R used instead.
> pnorm(120, 118.5, 1.2)
> ## [1] 0.8943502
> pnorm(116,118.5,1.2)
> ## [1] 0.01861043
> pnorm(120, 118.5, 1.2) - pnorm(116,118.5,1.2) ## [1] 0.8757398
> 
> 
> The second question is worded in a very horrible way. For the purposes of this calculation, the mean and the point of interest are reversed, that is, assume the mean is 115 (temporarily) and look for the point that would have the requisite 12.1% above it.
> Again, I used R:
> qnorm(0.121, 115, 1.2, lower.tail=FALSE) ## [1] 116.40
> 
> I think the first question is fairly standard intro content, but the second is assuming a bit more knowledge of the ability to invert the problem and I wouldn't consider it reasonable to use in a test or exam.
> 
> Jonathan
> 
> -----Original Message-----
> From: Blindmath [mailto:blindmath-bounces at nfbnet.org] On Behalf Of 
> Sabra Ewing via Blindmath
> Sent: Wednesday, 21 September 2016 1:08 p.m.
> To: blindmath at nfbnet.org
> Cc: Sabra Ewing
> Subject: [Blindmath] Statistics help
> 
> I need help with this statistics problem because I don't have access to many of the formulas  in my class. I tried to work with a group, but they haven't been very nice. They have just said that we went over it in class, when I can't understand what my professor writes on the board, and have received very little material in an accessible format. Anyways, here's the problem.
> 
> A large number of voltages show a mean of 118.5V and a population standard deviation of 1.20V. Determine the percentage of data that falls between 116 and 120 Volts. If it is desired to have 12.1% of the voltage below 115V, how should the mean voltage be adjusted? The dispersion is σ = 1.20 V.
> 
> I know it has something to do with the empirical rule, but I don't know what to do because it doesn't fall an even number of standard deviations from the mean. For the second part of the problem, I have no idea what to do.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Sabra Ewing
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