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> The only evidence PG needs is that people continue to spend money on private schools in order to increase university admissions. No, he also needs to prove t

> The only evidence PG needs is that people continue to spend money on private schools in order to increase university admissions. No, he also needs to prove that the people from those private schools aren't in fact smarter than people from public schools who attend the same universities. Especially due to affirmative action, which has immense impacts on how people are selected to attend college. We know people who send their kids to private schools tend to 1) have more money, 2) be more involved in their kids education, 3) more commonly have two-parent households. In short, they tend to be more successful and lots of that success can come from intelligence, however defined. I am the first to poo-poo the academic establishment, but PG's reasoning is shoddy and I would be highly surprised if any data showed this to be true.

deleted 5y ago
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torstenvl 5y ago
Please don't argue just to argue. PG is applying the very well known phenomenon of collider bias, a/k/a Berkson's Paradox. I have linked to a very thorough but approachable explanation of this phenomenon in a similar context (applicants for jobs rather than university). This phenomenon is extremely well-established and PG's reasoning is flawless. His premise may or may not be accurate — perhaps private schooling doesn't make an applicant more attractive — but he offered his justification for that assumption. If you have evidence to the contrary, please share it. If you can disprove collider bias, please share it, and be sure to let HN know when you get your economics or biostatistics Ph.D. for that dissertation, because it would be pretty groundbreaking.
- perl4ever 5y ago
  I graduated from a public high school and a public university, so I'm going to point out a seeming inconsistency with what you wrote and the web page that was linked to. After checking out the Wikipedia page on Berkson's Paradox, I'm not as sure as I was about my original reasons for disagreeing with you and Graham, but I found a thread I want to pull on. On the Wikipedia page, in discussing a hypothetical situation where the quality of burgers and fries may be positively correlated, but may also be observed to be negatively correlated due to the paradox, it says: "...because they would likely not eat anywhere where both were bad, they fail to allow for the large number of restaurants in this category which would weaken or even flip the correlation" I want to call your attention to the phrase "which would weaken or even flip the correlation". This appears to logically imply that the positive correlation might not be eliminated or flipped, depending on specific circumstances. Therefore your comments such as "[academic performance and private schooling] will be negatively correlated within each student body" (emphasis mine), seem overstated or overconfident. My gut reaction at first was simply that there is an implicit ceteris paribus that's taking too much load here; people aren't assigned to public and private schools at random, and I think that's essentially the same thing as abernard1 was expressing. However, I can't say I completely intuitively understand the paradox, so apart from that, I question whether you are really stating the same principle as is generally accepted. You wrote "you don't need data" and then asked for contrary evidence. If in fact, data is not required, then how can there be contrary evidence?
  - torstenvl 5y ago
    >> because they would likely not eat anywhere where both were bad, they fail to allow for the large number of restaurants in this category which would weaken or even flip the correlation > This appears to logically imply that the positive correlation might not be eliminated or flipped, depending on specific circumstances. No. The negative correlation. The text you quoted is explaining why the negative correlation is observed, even though the underlying population data might show a weaker negative correlation or even a positive correlation. Berkson's paradox is essentially a sampling error. Read it as "anecdotes have sampling bias when competitive market conditions force a trade off in qualities observed anecdotally." The only evidence necessary to show it applies is that there's an economic trade-off: Google hiring people based on experience and coding competitions, singles choosing dates based on personableness and attractiveness, schools admitting students based on educational pedigree and academic performance. > You wrote "you don't need data" and then asked for contrary evidence. That isn't remotely what happened. I believe you may be conflating my discussion of apples with my discussion of schools. I encourage you to try to say only true things about others' positions, please.
    - perl4ever 5y ago
      >The text you quoted is explaining why the negative correlation is observed Yes, and it is clearly describing the possibility it shows up, which is inconsistent with it always being the case. I'm trying to condense my point as much as I can. >The only evidence necessary to show it applies is that there's an economic trade-off This looks to me like essentially the same statement as I was referring to - "you don't need data". There is an economic tradeoff, and that's all we need to know. I am not telling you it's a fallacy to reject the possibility of contrary evidence. I'm saying that I doubt the principle is actually that powerful because of the qualified language I've mentioned already. >That isn't remotely what happened From my point of view, you just made the same claim again, so let's avoid the meta-argument and not start rehashing who said what. It only makes misunderstandings worse.
      - deleted 5y ago
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torstenvl 5y ago

Please don't argue just to argue. PG is applying the very well known phenomenon of collider bias, a/k/a Berkson's Paradox. I have linked to a very thorough but approachable explanation of this phenomenon in a similar context (applicants for jobs rather than university). This phenomenon is extremely well-established and PG's reasoning is flawless. His premise may or may not be accurate — perhaps private schooling doesn't make an applicant more attractive — but he offered his justification for that assumption. If you have evidence to the contrary, please share it. If you can disprove collider bias, please share it, and be sure to let HN know when you get your economics or biostatistics Ph.D. for that dissertation, because it would be pretty groundbreaking.

perl4ever 5y ago
I graduated from a public high school and a public university, so I'm going to point out a seeming inconsistency with what you wrote and the web page that was linked to. After checking out the Wikipedia page on Berkson's Paradox, I'm not as sure as I was about my original reasons for disagreeing with you and Graham, but I found a thread I want to pull on. On the Wikipedia page, in discussing a hypothetical situation where the quality of burgers and fries may be positively correlated, but may also be observed to be negatively correlated due to the paradox, it says: "...because they would likely not eat anywhere where both were bad, they fail to allow for the large number of restaurants in this category which would weaken or even flip the correlation" I want to call your attention to the phrase "which would weaken or even flip the correlation". This appears to logically imply that the positive correlation might not be eliminated or flipped, depending on specific circumstances. Therefore your comments such as "[academic performance and private schooling] will be negatively correlated within each student body" (emphasis mine), seem overstated or overconfident. My gut reaction at first was simply that there is an implicit ceteris paribus that's taking too much load here; people aren't assigned to public and private schools at random, and I think that's essentially the same thing as abernard1 was expressing. However, I can't say I completely intuitively understand the paradox, so apart from that, I question whether you are really stating the same principle as is generally accepted. You wrote "you don't need data" and then asked for contrary evidence. If in fact, data is not required, then how can there be contrary evidence?
- torstenvl 5y ago
  >> because they would likely not eat anywhere where both were bad, they fail to allow for the large number of restaurants in this category which would weaken or even flip the correlation > This appears to logically imply that the positive correlation might not be eliminated or flipped, depending on specific circumstances. No. The negative correlation. The text you quoted is explaining why the negative correlation is observed, even though the underlying population data might show a weaker negative correlation or even a positive correlation. Berkson's paradox is essentially a sampling error. Read it as "anecdotes have sampling bias when competitive market conditions force a trade off in qualities observed anecdotally." The only evidence necessary to show it applies is that there's an economic trade-off: Google hiring people based on experience and coding competitions, singles choosing dates based on personableness and attractiveness, schools admitting students based on educational pedigree and academic performance. > You wrote "you don't need data" and then asked for contrary evidence. That isn't remotely what happened. I believe you may be conflating my discussion of apples with my discussion of schools. I encourage you to try to say only true things about others' positions, please.
  - perl4ever 5y ago
    >The text you quoted is explaining why the negative correlation is observed Yes, and it is clearly describing the possibility it shows up, which is inconsistent with it always being the case. I'm trying to condense my point as much as I can. >The only evidence necessary to show it applies is that there's an economic trade-off This looks to me like essentially the same statement as I was referring to - "you don't need data". There is an economic tradeoff, and that's all we need to know. I am not telling you it's a fallacy to reject the possibility of contrary evidence. I'm saying that I doubt the principle is actually that powerful because of the qualified language I've mentioned already. >That isn't remotely what happened From my point of view, you just made the same claim again, so let's avoid the meta-argument and not start rehashing who said what. It only makes misunderstandings worse.
    - deleted 5y ago
      [deleted]