Kevin's Watch

Well, the punchline is debatable in whether it is good, but it is there. This one isn't preachy at all.

In statistical analysis of experiments, you'll see two phrases crop up quite a bit. "Reject the null hypothesis" and "fail to reject the null hypothesis." If you reject the null hypothesis, then you have enough evidence to think that your hypothesis is true (with some margin of error). If you fail to reject it, then you do not have enough evidence from this experiment to think that your hypothesis is true (with some margin of error).

In very early labs for science classes you'll often conduct basic experiments where you "reject the null hypothesis." So here, we see the guy talking about how they "rejected the null hypothesis years ago," treating it as a static hypothesis across all experiments that can simply be refuted.


Well, the punchline is debatable in whether it is good, but it is there. This one isn't preachy at all.

In statistical analysis of experiments, you'll see two phrases crop up quite a bit. "Reject the null hypothesis" and "fail to reject the null hypothesis." If you reject the null hypothesis, then you have enough evidence to think that your hypothesis is true (with some margin of error). If you fail to reject it, then you do not have enough evidence from this experiment to think that your hypothesis is true (with some margin of error).

In very early labs for science classes you'll often conduct basic experiments where you "reject the null hypothesis." So here, we see the guy talking about how they "rejected the null hypothesis years ago," treating it as a static hypothesis across all experiments that can simply be refuted.

the Null Hypoithesis basically means you assume there's 'nothing interesting here': There's no conclusive evidence that the thing you're testing for does anything / pushes anything in the direction you want it to. You generally reject it when your data suggests results this odd (assuming the null hypothesis) are less than 5% likely (called '95% confidence level', 95% and 99% are common). This does NOT suggest your alternative hypothesis is 95% likely to be correct. It could be a fluke, it could depend on something completely different that is just correlated to (tends to occur at the same time as) the thing you're testing for.

The comic works in several ways: Highlighting common ignorance about terms very important to how technology/science move on; this should arguably be taught to everyone at school. A particular null hypothesis is rejected in any study that has an interesting result.

It could also be criticism of a perceived trend that threatens sound science: Big industries (and some political / religious groups) are accused of throwing money into big studies (statistics works best with big numbers of test cases, preferably you also want to test against expected sources of error... that's a lot of work, so bigger is better) until they have the results they want. The comic takes it one step further: A 'big study' has disproved the concept of the Null hypothesis and killed sound science as we know it.

Seems more like a Loresraat topic than Gen Dis. Maybe even the Close, since statistics are often nothing more than perception, able to say whatever you want them to say. But, of course, not as many people read those forums, eh? Heh. So where is this from?

It's from sarge's randomness.

Congrats, this kitten was deathly allergic to randomness:

MsMary wrote:It's from sarge's randomness.

No it's not. He stole it from another site. Here's the site he took it from.

Wait, I want the original xkcd comic!

What good is an xkcd comic without the mouseover?

xkcd.com/892/

dANdeLION wrote:

MsMary wrote:It's from sarge's randomness.

No it's not. He stole it from another site. Here's the site he took it from.

i was planning a link after the questions mister jump.

Counternull

From Wikipedia, the free encyclopedia

In statistics, and especially in the statistical analysis of psychological data, the counternull is a statistic used to aid the understanding and presentation of research results. It revolves around the effect size, which is the mean magnitude of some effect divided by the standard deviation.

The counternull value is the effect size that is just as well supported by the data as the null hypothesis. In particular, when results are drawn from a distribution that is symmetrical about its mean, the counternull value is exactly twice the observed effect size.

The null hypothesis is a hypothesis set up to be tested against an alternative. Thus the counternull is an alternative hypothesis that, when used to replace the null hypothesis, generates the same p-value as had the original null hypothesis of “no difference.”

Some researchers contend that reporting the counternull, in addition to the p-value, serves to counter two common errors of judgment:
assuming that failure to reject the null hypothesis at the chosen level of statistical significance means that the observed size of the "effect" is zero; and
assuming that rejection of the null hypothesis at a particular p-value means that the measured "effect" is not only statistically significant, but also scientifically important.

These arbitrary statistical thresholds create a discontinuity, causing unnecessary confusion and artificial controversy.

Other researchers prefer confidence intervals as a means of countering these common errors.

I didn't know xkcd comics had a mouseover! Thanks, MsMary!

Renull failure

wikipedia wrote:Renull failure or kidney failure (formerly called renull insufficiency) describes a medical condition in which the kidneys fail to adequately filter toxins and waste products from the blood. The two forms are acute (acute kidney injury) and chronic (chronic kidney disease); a number of other diseases or health problems may cause either form of renull failure to occur.
Renull failure is described as a decrease in glomerular filtration rate. Biochemically, renull failure is typically detected by an elevated serum creatinine level. Problems frequently encountered in kidney malfunction include abnormal fluid levels in the body, deranged acid levels, abnormal levels of potassium, calcium, phosphate, and (in the longer term) anemia as well as delayed healing in broken bones. Depending on the cause, hematuria (blood loss in the urine) and proteinuria (protein loss in the urine) may occur. Long-term kidney problems have significant repercussions on other diseases, such as cardiovascular disease.

MsMary wrote:What good is an xkcd comic without the mouseover? /

Yeah, pretty much just half an xkcd comic...

Linna Heartlistener wrote:

MsMary wrote:What good is an xkcd comic without the mouseover? /

Yeah, pretty much just half an xkcd comic...

That's what I'm sayin'.

Glad to help out, ali.

Of no legal validity, force, or effect; nothing. As used in the phrase null and void, refers to something that binds no one or is incapable of giving rise to any rights or duties under any circumstances.

null (Insignificant), adjective beneath notice, disregarded, empty, expendable, immaterial, impuissant, inappreciable, inconsequential, inconsiderable, inferior, insubstantial, insufficient, irrelevant, meaningless, minor, negligible, nominal, nugatory, of no account, of no effect, of no moment, of no value, paltry, petty, pointless, powerless, puny, secondary, small, superficial, tenuous, token, trifling, trivial, unavailing, unessential, unimportant, uninfluential, unmeaningful, unnecessary, unsubstantial, useless, valueless, without conseeuence, without meaning, without significance, without substance, worthless

Having some self-esteem issues lately, sgt?

Heheh. Took me a while to get it also. D'oh!

aliantha wrote:I didn't know xkcd comics had a mouseover! Thanks, MsMary!

Wow, are you in for a treat... you get to read the whole series again from the start, and see the other half of the jokes

Fist and Faith wrote:Having some self-esteem issues lately, sgt?

I have got a field that has been setup to allow for Null, but am now wanting to change that to not allow for Null.

When ever I try to change this I can't because PhpMyAdmin has set all the previous records to Null.

How can I fix this problem?

Is there a query I could put that will remove all the Null values and set the field to Non Null?

Of course. But what do you you mean by "remove all the NULL values?" Does that mean to delete all the rows that have a NULL in that field? If so, you could do this:
DELETE FROM your_table WHERE your_field IS NULL;

If you want to keep those rows, you'll have to put some other value in that field. Is there one that makes sense? If so, you could do this:
UPDATE your_table SET your_field = 42 WHERE your_field IS NULL;

(Where, of course, 42 is whatever value you want to use instead.)

If you want to keep the rows, and there isn't any other value you could use, then the NULLs that are there now should stay, and it might be time to reevaluate why you want to set the field to NOT NULL.

Rigel wrote:

aliantha wrote:I didn't know xkcd comics had a mouseover! Thanks, MsMary!

Wow, are you in for a treat... you get to read the whole series again from the start, and see the other half of the jokes

Yes, indeed.

And always glad to help out, Ali.

A 3+1 perspective on null hypersurfaces and isolated horizons

E. Gourgoulhon, J.L. Jaramillo (LUTH, CNRS / Observatoire de Paris)

(Submitted on 29 Mar 2005 (v1), last revised 26 Oct 2005 (this version, v2))

The isolated horizon formalism recently introduced by Ashtekar et al. aims at providing a quasi-local concept of a black hole in equilibrium in an otherwise possibly dynamical spacetime. In this formalism, a hierarchy of geometrical structures is constructed on a null hypersurface. On the other side, the 3+1 formulation of general relativity provides a powerful setting for studying the spacetime dynamics, in particular gravitational radiation from black hole systems. Here we revisit the kinematics and dynamics of null hypersurfaces by making use of some 3+1 slicing of spacetime. In particular, the additional structures induced on null hypersurfaces by the 3+1 slicing permit a natural extension to the full spacetime of geometrical quantities defined on the null hypersurface. This 4-dimensional point of view facilitates the link between the null and spatial geometries. We proceed by reformulating the isolated horizon structure in this framework. We also reformulate previous works, such as Damour's black hole mechanics, and make the link with a previous 3+1 approach of black hole horizon, namely the membrane paradigm. We explicit all geometrical objects in terms of 3+1 quantities, putting a special emphasis on the conformal 3+1 formulation. This is in particular relevant for the initial data problem of black hole spacetimes for numerical relativity. Illustrative examples are provided by considering various slicings of Schwarzschild and Kerr spacetimes.

Ron Burgunihilo wrote:Heheh. STill me a while to not get it also. D'oh!