Comments on: Homework #1: Answer part II

By: TCO

TCO — Mon, 05 May 2008 00:57:06 +0000

And please move the bookmark thing to the other side of the comment post or get rid of it or something. I hit it every time I try to post.

By: TCO

TCO — Mon, 05 May 2008 00:48:04 +0000

BIGGER FONT PLEASE!

By: Chuck Peterson

Chuck Peterson — Mon, 31 Mar 2008 17:57:04 +0000

Imagine the study done in 10 random cities worldwide in 10 locations each (ranked say into 10 economic zones, 5 easily near transportation and 5 not or something, where we get a representative mix of people). Percentage of people using an electronic device of some sort; computer, cell phone, music player. Results for each city:

1, 20, 15, 8, 30, 55, 45, 2, 18, 5

“A recent study of cities worldwide shows one out of five people uses some sort of electronic device when outside.”

Even if the same number were counted in each location in each city (say 1000 each) and the cities are somewhat fairly dispersed and not all alike, does that 20% really tell us anything? Also, perhaps the next day the numbers would be vastly different. And where were the locations of the places with the lower percentages versus higher? What time of day? Places where 1000 people were observed in what period of time versus another? This tells us nothing.

By: Bruce Foutch

Bruce Foutch — Thu, 27 Mar 2008 18:31:08 +0000

Good morning Dr. Briggs,

“horror vacui”

I see an empty green tab at the top of your blog page. I wonder if you would consider making it into a “References” tab, providing links to references mentioned in your blog and/or to information, including your past blog entries, that you think might provide some of us non-statistician folks a core of basic information that we can refer to, to better follow along with your teachings.

Perhaps the following paper and rebuttal might be candidates:

# Published August 30, 2005 - ESSAY Why Most Published Research Findings Are False Ioannidis JPA PLoS Medicine Vol. 2, No. 8, e124 doi:10.1371/journal.pmed.0020124

# Published April 24, 2007 - CORRESPONDENCE Why Most Published Research Findings Are False: Problems in the Analysis Goodman S, Greenland S PLoS Medicine Vol. 4, No. 4, e168 doi:10.1371/journal.pmed.0040168

By: Martin Ringo

Martin Ringo — Thu, 27 Mar 2008 15:52:46 +0000

Suppose your model were the following:
The probability of any individual wearing the device, D, is a function of the group (read age, sex, nationality, education, etc. etc.), the time (hour, day of week, etc.), some random component, which we might call taste preferences, and whether the individual was wearing the device in period t-1.
P(i(g),t) = f( g, t, error) + rho*X(i,t-1)

Now if we take a single sample, even very large, we have both a nasty problem with the distribution of the estimator — probably can only get it with empirical methods — and a nastier problem of sampling. We certainly don’t have the classical random sample with i.i.d. variates.

If I told you that group probabilities (for some “average” t and error) were essentially uniform, wouldn’t you have a tendency to ignore any one or two or M-1 samples (where M being the smallest number to feel confident about the distribution of group probabilities)?

Anyway, while I am not an epidemiologist — although I do get sick — it seems that the basic problem is one of epidemiology, at least to assessing the population propensity of incidence or carrying.

By: Bernie

Bernie — Thu, 27 Mar 2008 14:40:31 +0000

I think the big belly linked to dementia story fits into this topic.
See for example http://abcnews.go.com/Health/wireStory?id=4534488
First, I hasten to add that I am not overweight and have a 34″ waist.
What struck me was how poorly articulated were the findings from this study - which is also over 2 years old to boot. The logic boils down to - we see a correlation between body shape and dementia, therefore something that is associated with body shape causes changes in the brain that leads to dementia. At this point, the authors would have been better of saying
“we are not certain if this reflects a real causal relationship and if there is a real causal relationship what the nature of that process is.”
But the then the reporter would be forced to ask themselves is the story worth printing. Insurance companies - like Kaiser Permanate who sponsored the study - may simply take the actuarial view and scare the fat of people.

By: steven mosher

steven mosher — Thu, 27 Mar 2008 14:19:17 +0000

Would be nice to get a baysian angle on Lucias work.. Mostly so I could get a grasp of the baysian thing

By: Dan Hughes

Dan Hughes — Thu, 27 Mar 2008 14:04:59 +0000

re: # 20

And lucia and tamino, too. And of course tamino and Steve McIntyre on PCA.

It’s all getting very confusing to me.

If stats was maths we wouldn’t be in this situation. In maths either it is or it isn’t. Plus some physical causality would be very helpful.

By: Mike D.

Mike D. — Thu, 27 Mar 2008 06:49:25 +0000

Dr. Briggs,

I apologize. It was late and I wasn’t thinking. I love your blog and look forward to your treatise on the mysticism of randomness. I hope you also touch on the Laws of Probability and why they aren’t called theories.

I agree that philosophy matters. Statistics is more than playing with numbers; it is the mathematical language of rationality and the scientific method. It is the Cult of Logical Inference, and as a card-carrying cultist I accept on faith that logical inferences exist. Propositions are either probably true or probably false, and we can measure the probability, but only because the Truth is out there somewhere. The moderns and classicals are not different in that respect.

As for looking good, you’ll have to go some to beat Miss Teen South Carolina in a short skirt. But this blog is exploring some lovely ideas, so I’ll have to factor that in.

PS Are you saying that even though A Rod bats .333, he never gets a third of a hit?

By: mr b

mr b — Thu, 27 Mar 2008 05:13:12 +0000

going the distance—I will.