janos

Karma: 239

janos Mar 14, 2011, 7:15 PM
3 points
in reply to: benelliott’s comment on: Science Journalism and How To Present Probabilities [Link]
Nope: the odds ratio was (.847/(1-.847))/(.906/(1-.906)), which is indeed 57.5%, which could be rounded to 60%. If the starting probability was, say, 1%, rather than 90.6%, then translating the odds ratio statement to “60% as likely” would be legitimate, and approximately correct; probably the journalist learned to interpret odds ratios via examples like that. But when the probabilities are close to 1, it’s more correct to say that the women/blacks were 60% more likely to not be referred.

janos Mar 4, 2011, 3:23 AM
0 points
in reply to: jsalvatier’s comment on: What Else Would I Do To Make a Living?
It’s just a vanilla (MH) MCMC sampler for (some convenient family of) distributions on polytopes; hopefully like this: http://cran.r-project.org/web/packages/limSolve/vignettes/xsample.pdf , but faster. It’s motivated by a model for inferring network link traffic flows from counts of in- and out-bound traffic at each node; the solution space is a polytope, and we want to take advantage of previous observations to form a better prior. But for the approach to be feasible we first need to sample.

But this is not a long-term project, I think.

janos Mar 4, 2011, 3:13 AM
0 points
in reply to: jsteinhardt’s comment on: What Else Would I Do To Make a Living?
Looks like good stuff … thanks for the tip.

janos Mar 4, 2011, 2:59 AM
1 point
in reply to: jsalvatier’s comment on: What Else Would I Do To Make a Living?
Currently I’m taking classes and working on a polytope sampler. I tend to be excited about Bayesian nonparametrics and consistent families of arbitrary-dimensional priors. I’m also excited about general-purpose MCMC-like approaches, but so far I haven’t thought very hard about them.

janos Mar 2, 2011, 9:58 PM
8 points
on: What Else Would I Do To Make a Living?
In undergrad I feared a feeling of locked-in-ness, and ditched my intention to do a PhD in math (which I think I could have done well in) partly for this reason, though it was also easier for me because I hadn’t established close ties to a particular line of research, and because I had programming background. I worked a couple of years in programming, and now I’m back in school doing a PhD in stats, because I like probability spaces and because I wanted to do something more mathematical than (most) programming. I guess I picked stats over applied math partly out of the same worry about overspecialization; I think stats has a bigger wealth of better-integrated more widely applicable concepts/insights.

janos Feb 14, 2011, 1:36 AM
2 points
in reply to: CronoDAS’s comment on: Open Thread: Mathematics
Would you be surprised if the absolute value was bigger than 3^^^3? I’m guessing yes, very much so. So that’s a reason not to use an improper prior.

If there’s no better information about the problem, I sortof like using crazy things like Normal(0,1)*exp(Cauchy); that way you usually get reasonable smallish numbers, but you don’t become shocked by huge or tiny numbers either. And it’s proper.

janos Feb 12, 2011, 7:46 AM
0 points
in reply to: Dreaded_Anomaly’s comment on: An Abortion Dialogue
I wasn’t trying to present a principled distinction, or trying to avoid bias. What I was saying isn’t something I’m going to defend. The only reason I responded to your criticism of it was that I was annoyed by the nature of your objection. However, since now I know you thought I was trying to say more than I actually was, I will freely ignore your objection.

janos Feb 12, 2011, 6:48 AM
0 points
in reply to: Dreaded_Anomaly’s comment on: An Abortion Dialogue
Do you have an instance of “I proactively do X” where you do not class it as reactive? Do you have an instance of “I wish to avoid Y” where you do not class it as specific? I don’t like conversations about definitions. I was using these words to describe a hypothetical inner experience; I don’t claim that they aren’t fuzzy. You seem to be pointing at the fuzziness and saying that they’re meaningless; I don’t see why you’d want to do that.

janos Feb 12, 2011, 5:58 AM
−2 points
in reply to: Dreaded_Anomaly’s comment on: An Abortion Dialogue
It seems to me that we mean different things by the words “reactive” (as opposed to proactive) and “specific”. A weak attempt at a reductio: I proactively do X to avoid facing Y; I am thus reacting to my desire to avoid facing Y. And is Y general or specific? Y is the specific Y that I do X to avoid facing.

janos Feb 12, 2011, 5:38 AM
3 points
in reply to: Alicorn’s comment on: An Abortion Dialogue
Ah, yes indeedy true. I guess I was thinking of abstinence. So wrong distinction. More likely, then: abortion is done to a specific embryo who is thereby prevented from being, and it’s done reactively; there’s no question that when you have an abortion it’s about deciding to kill this particular embryo. Contraceptive use on the other hand is nonspecific and proactive; it doesn’t feel like “I discard these reproductive cells which would have become a person!”, it feels like exerting prudent control over your life.

janos Feb 12, 2011, 4:10 AM
5 points
in reply to: PlaidX’s comment on: An Abortion Dialogue
I agree with your main point (that this is a stumbling block for some people), but there are others who will contend that A and part of B (namely the irreversible error) do apply to unwanted babies (usually, or on average), and that the reason why abortion is more evil than contraception is because it’s an error of commission rather than omission.

janos Feb 9, 2011, 4:57 AM
3 points
in reply to: Conuly’s comment on: Procedural Knowledge Gaps
But I drink orange juice with pulp; then the fiber is no longer absent, though I guess it’s reduced. The vitamins and minerals are still present, though, aren’t they?

janos Feb 8, 2011, 3:30 AM
3 points
in reply to: nazgulnarsil’s comment on: Procedural Knowledge Gaps
Regarding the fruit juices, I agree that fruit-flavored mixtures of HFCS and other things generally aren’t worth much, but aren’t proper fruit juices usually nutritious? (I mean the kinds where the ingredients consist of fruit juices, perhaps water, and nothing else.)

janos Feb 7, 2011, 4:23 AM
14 points
on: Procedural Knowledge Gaps
Regarding investment, my suggestion (if you work in the US) is to open a basic (because it doesn’t periodically charge you fees) E*TRADE account here. They will provide an interface for buying and selling shares of stocks and various other things (ETFs and such; I mention stocks and ETFs because those are the only things I’ve tried doing anything with). They will charge you $10 for every transaction you make, so unless you’re going to be (or become) active/clever enough to make it worthwhile, it makes sense not to trade too frequently.

EDIT: These guys appear to charge less, though they also deal in fewer things (e.g. no bonds).
What links here?
- Topics from “Procedural Knowledge Gaps” by NancyLebovitz (Feb 11, 2012, 9:38 PM; 58 points)
- Unnamed's comment on How can I make money? by Goobahman (Apr 21, 2011, 3:32 AM; 11 points)

janos Feb 6, 2011, 6:37 PM
3 points
on: A bit meta: Do posts come in batches? If so, why?
Echoing the others:

If we suppose these are 22 iid samples from a Poisson then the max likelihood estimate for the Poisson parameter is 0.82 (the sample mean). Simulating such draws from such a Poisson and looking at sample correlation between Jan 15-Feb 4 and Jan 16-Feb 5, the p-value is 0.1. And when testing Poisson-ness vs negative binomial clustering (with the same mean), the locally most powerful test uses statistic (x-1.32)^2, and gives a simulated p-value of 0.44.

janos Feb 6, 2011, 3:54 AM
13 points
in reply to: Alicorn’s comment on: My hour-long interview with Yudkowsky on “Becoming a Rationalist”
It’s provided in the linked page; you need to scroll down to see it.

janos Dec 12, 2009, 6:14 AM
1 point
in reply to: HalFinney’s comment on: Probability Space & Aumann Agreement
What I don’t like about the example you provide is: what player 1 and player 2 know needs to be common knowledge. For instance if player 1 doesn’t know whether player 2 knows whether die 1 is in 1-3, then it may not be common knowledge at all that the sum is in 2-6, even if player 1 and player 2 are given the info you said they’re given.

This is what I was confused about in the grandparent comment: do we really need I and J to be common knowledge? It seems so to me. But that seems to be another assumption limiting the applicability of the result.

janos Dec 11, 2009, 4:42 PM
0 points
in reply to: Psy-Kosh’s comment on: Probability Space & Aumann Agreement
As far as I understand, agent 1 doesn’t know that agent 2 knows A2, and agent 2 doesn’t know that agent 1 knows A1. Instead, agent 1 knows that agent 2′s state of knowledge is in J and agent 2 knows that agent 1′s state of knowledge is in I. I’m a bit confused now about how this matches up with the meaning of Aumann’s Theorem. Why are I and J common knowledge, and {P(A|I)=q} and {P(A|J)=q} common knowledge, but I(w) and J(w) are not common knowledge? Perhaps that’s what the theorem requires, but currently I’m finding it hard to see how I and J being common knowledge is reasonable.

Edit: I’m silly. I and J don’t need to be common knowledge at all. It’s not agent 1 and agent 2 who perform the reasoning about I meet J, it’s us. We know that the true common knowledge is a set from I meet J, and that therefore if it’s common knowledge that agent 1′s posterior for the event A is q1 and agent 2′s posterior for A is q2, then q1=q2. And it’s not unreasonable for these posteriors to become common knowledge without I(w) and J(w) becoming common knowledge. The theorem says that if you’re both perfect Bayesians and you have the same priors then you don’t have to communicate your evidence.

But if I and J are not common knowledge then I’m confused about why any event that is common knowledge must be built from the meet of I and J.

janos Dec 11, 2009, 4:10 PM
0 points
in reply to: Psy-Kosh’s comment on: Probability Space & Aumann Agreement
That simplification is a situation in which there is no common knowledge. In world-state w, agent 1 knows A1 (meaning knows that the correct world is in A1), and agent 2 knows A2. They both know A1 union A2, but that’s still not common knowledge, because agent 1 doesn’t know that agent 2 knows A1 union A2.

I(w) is what agent 1 knows, if w is correct. If all you know is S, then the only thing you know agent 1 knows is I(S), and the only thing that you know agent 1 knows agent 2 knows is J(I(S)), and so forth. This is why the usual “everyone knows that everyone knows that … ” definition of common knowledge translates to I(J(I(J(I(J(...(w)...).

janos Dec 11, 2009, 3:48 PM
0 points
in reply to: AndrewKemendo’s comment on: Probability Space & Aumann Agreement
Huh? The reference set Ω is the set of possible world histories, out of which one element is the actual world history. I don’t see what’s wrong with this.