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18 Mar 02:43

Saturday Morning Breakfast Cereal - Inaccuracy

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Once every few weeks, he wakes up in a cold sweat because he had a dream that used an inaccurate star map.

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Written with love.

18 Mar 02:42

Saturday Morning Breakfast Cereal - Anything

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Today's comic based on something Bryan Caplan wrote in his (ever so slightly) controversial 'The Case Against Education.' I think he was mentioning it as a problem, not a strategy, but hey... tomAYto tomAHto.

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18 Mar 02:36

Saturday Morning Breakfast Cereal - Diet

by tech@thehiveworks.com


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In all likelihood, you are already on this diet. Congrats on sticking to it!

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17 Mar 23:45

Saturday Morning Breakfast Cereal - Hair

by tech@thehiveworks.com


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It's called TRUST, Sharon.

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Last full day to get BAHFest tickets!

17 Mar 23:10

Saturday Morning Breakfast Cereal - QUACK

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I'm just saying, if this ever HAS happened, there probably wouldn't be an announcement.

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17 Mar 23:09

Saturday Morning Breakfast Cereal - Joyce

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Fun fact: In the middle of every Derrida book, there are nuclear launch codes, the recipe for Coca Cola, and the location of Blackbeard's gold.

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17 Mar 23:09

Saturday Morning Breakfast Cereal - Burial Ground

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Some of them are trapped in a ghostly cycle, forever arguing on twitter.

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Just 1.5 weeks until BAHFest Houston and tickets are selling fast!

17 Mar 23:04

Clarification

by Doug

Clarification

Happy Pi Day!

For the record, I can list 17 digits of pi, but only because of the magic of Andrew Huang.

17 Mar 23:02

Can’t Buy It

by Doug
17 Mar 22:58

Robot Future

I mean, we already live in a world of flying robots killing people. I don't worry about how powerful the machines are, I worry about who the machines give power to.
17 Mar 22:53

The History of Unicode

2048: "Great news for Maine—we're once again an independent state!!! Thanks, @unicode, for ruling in our favor and sending troops to end New Hampshire's annexation. 🙏🚁🎖️"
17 Mar 22:52

New Things

by Reza

17 Mar 22:50

Yourself

by Reza

17 Mar 22:44

Sun Tzu

by ricardo coimbra
Clique na imagem para aumentar
17 Mar 22:42

Natural Enemies

by Doug

Natural Enemies

Happy Groundhog Day!

17 Mar 22:38

Viva Intensamente # 347

by Will Tirando

17 Mar 22:35

Stone Cold

by Reza

17 Mar 22:05

A practitioner’s guide to reading programming languages papers | the morning paper

by brandizzi

A practitioner’s guide to reading programming languages papers

January 26, 2018

Last week I jokingly said that POPL papers must pass an ‘intellectual intimidation’ threshold in order to be accepted. That’s not true of course, but it is the case that programming languages papers can look especially intimidating to the practitioner (or indeed, the academic working in a different sub-discipline of computer science!). They are full of dense figures with mathematical symbols, and phrases thrown around such as “judgements”, “operational semantics”, and the like. There are many subtle variations in notation out there, but you can get a long way towards following the gist of a paper with an understanding of a few basics. So instead of covering a paper today, I thought I’d write a short practitioner’s guide to decoding programming languages papers. I’m following Pierce’s ‘Types and Programming Languages’ as my authority here.

Syntax

Let’s start from a place of familiarity: syntax. The syntax tells us what sentences are legal (i.e., what programs we can write) in the language. The syntax comprises a set of terms, which are the building blocks. Taking the following example from Pierce:

  t ::= 
      true
      false
      if t then t else t
      0
      succ t
      pred t
      iszero t

Wherever the symbol t appears we can substitute any term. When a paper is referring to terms, the letter t is often used, many times with subscripts to differentiate between different terms (e.g., t_1, t_2). The set of all terms is often denoted by \tau. This is not to be confused with T, traditionally used to represent types.

Notice in the above that if on it’s own isn’t a term (it’s a token, in this case, a keyword token). The term is the if-expression if t then t else t.

Terms are expressions which can evaluated, and the ultimate results of evaluation in a well-formed environment should be a value. Values are a subset of terms. In the above example the values are true, false, 0 together with the values that can be created by successive application of succ to 0 (succ 0, succ succ 0, ...).

Semantics

We want to give some meaning to the terms in the language. This is the semantics. There are different ways of defining what programs mean. The two you’ll see referred to most often are operational semantics and denotational semantics. Of these, operational semantics is the most common, and it defines the meaning of a program by giving the rules for an abstract machine that evaluates terms. The specification takes the form of a set of evaluation rules — which we’ll look at in just a moment. The meaning of a term t, under this world view is the final state (the value) that the machine reaches when started with t as its initial state. In denotational semantics the meaning of a term is taken to be some mathematical object (e.g., a number or a function) in some preexisting semantic domain, and an interpretation function maps terms in the language to their equivalents in the target domain. (So we are specifying what each term represents, or denotes, in the domain).

You might also see authors refer to ‘small-step’ operational semantics and ‘big-step’ operational semantics. As the names imply, these refer to how big a leap the abstract machine makes with each rule that it applies. In small-step semantics terms are rewritten bit-by-bit, one small step at a time, until eventually they become values. In big-step semantics (aka ‘natural semantics’) we can go from a term to its final value in one step.

In small-step semantics notation, you’ll see something like this: t_1 \rightarrow t_2, which should be read as t_1 evaluates to t_2. (You’ll also see primes used instead of subscripts, e.g. t \rightarrow t'). This is also known as a judgement. The \rightarrow represents a single evaluation step. If you see t_1 \rightarrow^{*} t_2 then this means ‘by repeated application of single-step evaluations, t_1 eventually evaluates to t_2’.

In big-step semantics a different arrow is used. So you’ll see t \Downarrow v to mean that term t evaluates to the final value v. If we had both small-step and big step semantics for the same language, then t \rightarrow^{*} v and t \Downarrow v both tell us the same thing.

Rules are by convention named in CAPS. And if you’re lucky the authors will prefix evaluation rules with ‘E-‘ as an extra aid to tell you what you’re looking at.

For example:

if true then t2 else t3\rightarrow t2 (E-IFTRUE)

Most commonly, you’ll see evaluation rules specified in the inference rule style. For example (E-IF):

\displaystyle \frac{t_1\  \rightarrow t'_{1}}{\mathrm{if}\  t_1\  \mathrm{then}\  t_2\  \mathrm{else}\  t_3 \rightarrow \mathrm{if}\  t'_1\  \mathrm{then}\  t_2\  \mathrm{else}\  t_3}

These should be read as “Given the things above the line, then we can conclude the thing below the line.” In this particular example therefore, “Given that t_1 evaluates to t'_{1} then ‘\mathrm{if}\ t_1 ...’ evaluates to ‘\mathrm{if}\ t'_1 ...’.”

Types

A programming language doesn’t have to have a specified type system (it can be untyped), but most do.

A type system is a tractable syntactic method for proving the absence of certain program behaviours by classifying phrases according to the kinds of values they compute – Pierce, ‘Types and Programming Languages.’

The colon is used to indicate that a given term has a particular type. For example, t:T. A term is well-typed (or typable) if there is some T such that t : T. Just as we had evaluation rules, we can have typing rules. These are also often specified in the inference rule style, and may have names beginning with ‘T-‘. For example (T-IF):

\displaystyle \frac{t_1:\mathrm{Bool}\ \ t_2:\mathrm{T}\ \ t_3:\mathrm{T}}{\mathrm{if}\ t_1 \ \mathrm{then}\ t_2\ \mathrm{else}\ t_3\ : \ \mathrm{T}}

Which should be read as “Given that term 1 has type Bool, and term 2 and term 3 have type T, then the term ‘if term 1 then term 2 else term 3’ has type T”.

For functions (lambda abstractions) we also care about the type of the argument and the return value. We can annotate bound variables to specify their type, so that instead of just ‘\lambda x.t’ we can write ‘\lambda x:\mathrm{T_1} . t_2’. The type of a lambda abstraction (single argument function) is written \mathrm{T_1}\ \rightarrow\ \mathrm{T_2}, meaning it takes an argument of type \mathrm{T_1} and returns a result of type \mathrm{T_2}.

You’ll see the turnstile operator, \vdash, a lot in typing inference rules. ‘P \vdash Q’ should be read as “From P, we can conclude Q”, or “P entails Q”. For example, ‘x:\mathrm{T_1} \vdash t_2 : \mathrm{T_2}’ says “From the fact that x has type T1, it follows that term t2 has type T2.”

We need to keep track of variable bindings for the types of the free variables in a function. And to do that we use a typing context (aka typing environment). Think of it like the environment you’re familiar with that maps variable names to values, only here we’re mapping variable names to types. By convention Gamma (\Gamma) is the symbol used for the typing environment. It will often pop up in papers by convention with no explanation given. I remember what it represents by thinking of a gallows capturing the variables, with their types swinging from the rope. YMMV!! This leads to the three place relation you’ll frequently see, of the form \Gamma \vdash t : \mathrm{T}. It should be read, “From the typing context \Gamma it follows that term t has type T.” The comma operator extends \Gamma by adding a new binding on the right (e.g., ‘\Gamma, x:\mathrm{T}’).

Putting it all together, you get rules that look like this one (for defining the type of a lambda abstraction in this case)

\displaystyle \frac{\Gamma, x : \mathrm{T_1} \vdash t_2 : \mathrm{T_2}}{\Gamma \vdash \lambda x:\mathrm{T-1}.t_2 : \mathrm{T_1} \rightarrow \mathrm{T_2}}

Let’s decode it: “If (the part above the line), from a typing context with x bound to T1 it follows that t2 has type T2, then (the part below the line) in the same typing context the expression \lambda x:\mathrm{T_1}.t_2 has the type \mathrm{T_1} \rightarrow \mathrm{T_2}.”

Type Safety

If Jane Austen were to have written a book about type systems, she’d probably have called it “Progress and Preservation.” (Actually, I think you could write lots of interesting essays under that title!). A type system is ‘safe’ (type safety) if well-typed terms always end up in a good place. In practice this means that when we’re following a chain of inference rules we never get stuck in a place where we don’t have a final value, but neither do we have any rules we can match to make further progress. (You’ll see authors referring to ‘not getting stuck’ – this is what they mean). To show that well-typed terms don’t get stuck, it suffices to prove progress and preservation theorems.

  • Progress: a well-typed term is not stuck (either it is a value or it can take a step according to the evaluation rules).
  • Preservation: if a well-typed term takes a step of evaluation, then the resulting term is also well typed.

Sometimes you’ll see authors talking about progress and preservation without explicitly saying why they matter. Now you know!

Church, Curry, Howard, Hoare

A few other things you might come across that it’s interesting to be aware of:

  • In a Curry-style language definition, first terms are defined, then a semantics is given showing how they behave, and then a type system is layered on top that ‘rejects some terms whose behaviours we don’t like.’ Semantics comes before typing.
  • In a Church-style language definition typing comes before semantics, so we never have to ask what the behaviour of an ill-typed term is.
  • The Curry-Howard correspondence is a mapping between type theory and logic in which propositions in logic are treated like types in a type system. (aka, propositions as types). The correspondence can be used to transfer developments between the fields (e.g. linear logic and linear type sytems).
  • Hoare logic, or Hoare triples refers to statements of the kind {P}C{Q}. Which should be read as “If the pre-condition P is true, then when C is executed (and if it terminates), the post-condition Q will be true.”

I’m really just an interested outsider looking on at what’s happening in the community. If you’re reading this as a programming languages expert, and there are more things that should go into a practitioner’s crib sheet, please let us all know in the comments!

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17 Mar 22:05

NASA confirms it rediscovered satellite that disappeared 12-plus years ago | MLive.com

by brandizzi

NASA has confirmed an amateur astronomer's claim that he made contact with the space agency's IMAGE satellite that had been missing for more than 12 years.

The IMAGE spacecraft launched back in March 2000 and was "unexpectedly lost" on Dec. 18, 2005.

The U.S. space agency said that it successfully collected data from the satellite Tuesday afternoon, Jan. 30 from its Johns Hopkins Applied Physics Lab in Maryland. NASA reports it has been able to read some "basic housekeeping data" from IMAGE, which suggests its "main control system is operational." 

"Scientists and engineers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, will continue to try to analyze the data from the spacecraft to learn more about the state of the spacecraft," the space agency says in the release.

"This process will take a week or two to complete as it requires attempting to adapt old software and databases of information to more modern systems." 

The astronomer who said he discovered the still broadcasting IMAGE, Scott Tilley, told Science Magazine he was looking for a classified U.S. satellite, but instead picked up the one labeled "2000-017A" which belongs to NASA's long-lost $150 million mission's spacecraft.

NASA said in its Wednesday release that it received a signal ID of 166, which is the ID for IMAGE. 

The IMAGE spacecraft was originally launched to study the magnetosphere, which is the invisible magnetic field that surrounds the Earth. Science reports the mission was considered a success by NASA before it went missing. 

"IMAGE was designed to image Earth's magnetosphere and produce the first comprehensive global images of the plasma populations in this region," NASA reports in the release.

"After successfully completing and extending its initial two-year mission in 2002, the satellite unexpectedly failed to make contact on a routine pass on Dec. 18, 2005. After a 2007 eclipse failed to induce a reboot, the mission was declared over."

IMAGE was lost when NASA couldn't "establish a routine communication" with the Deep Space Network. The space agency's official report on the failure cited an unexpected error within the power system as the reason for its disappearance. 

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17 Mar 21:55

Preto no branco

by Tiago de Thuin
Neste carnaval, a questão da adequação moral de se usar fantasias foi uma das que mais ocuparam as classes tagarelantes das redes sociais brasileiras; dentro dessa questão, muito se falou sobre apropriação cultural, falando sobre as fantasias de índios (com direito a índios propriamente ditos se manifestando pró e contra; não vi ninguém do Cacique de Ramos se pronunciando ou sendo perguntado). O curioso dessa discussão, ao menos pra mim, foi que o grosso dela, entre as classes tagarelantes - ou melhor, entre o que eu vejo das classes tagarelantes - se deu de um ponto de vista branco e ocidental. Tanto as pessoas que denunciavam a apropriação cultural quanto aquelas que rejeitavam a noção o faziam a partir do ponto de vista de fazer parte de uma cultura branca e ocidental e majoritariamente como, eles mesmos, brancos.

Essa discussão já estava morrendo quando vi um chilro no twitter que comentava que "pelo visto só aqui no twitter reparamos e condenamos o blackface," condenando o fato de os jurados do Estandarte de Ouro terem entregue um estandarte ao Salgueiro, apesar da escola ter incorrido naquela prática condenável. O curioso dessa declaração é que, bem, presumivelmente os jurados do estandarte de ouro têm mais intimidade com a cultura popular brasileira, e especificamente a negra, do que a média das redes sociais. O chilro condenando, então, então é um caso particularmente explícito de um movimento antiracista que tem os EUA como norte, vide o próprio uso do termo em inglês blackface, que tem uma história específica naquele país associada aos minstrel shows, o que não elimina o valor negativo das caricaturas de negros perpetradas por atores brancos em outras plagas, mas faz uma diferença na tradução que é muitas vezes ignorada; não que, por sua vez, como nada disso é imutável, blackface, sendo ou não um problema genérico dentro do racismo brasileiro antes da influência americana, seja hoje aceitável, porque o problema é a ofensa presente, e não a verdade histórica (que por sua vez é sempre contingente). Só do que estou falando é que as visões do racismo e de seu enfrentamento, tanto por companheiro de viagem quanto pelos próprios negros, são mutáveis, e dependem tanto de vivências diretas quanto de influências culturais e intelectuais, históricas e internacionais. E, no Brasil, a maior dessas influências é a americana. 

Não estou falando disso, bem entendido, para entrar na discussão como mais um dos "nacionalistas do racismo" que rejeitam as noções americanas sobre o tema, seja para pregar uma visão única nacional, seja pra propalar as balelas da democracia racial pseudo-freyreana (nem Freyre acreditava numa democracia racial efetiva). Pelo contrário, o que acho curioso da assimilação dessas noções no Brasil é que essa influência é, quando se pensa na demografia brasileira, extremamente conveniente para os brancos. Afinal, o Brasil, que recebeu mais de treze vezes mais africanos cativos do que os EUA, e menos da quinta parte de imigrantes livres, não é, demograficamente, um país em que os negros, descendentes de escravos ou não, são uma minoria entre outras que convivem com uma maioria privilegiada branca. Pelo contrário, é um país em que negros e mestiços (de negro e índio) constituem a maioria da população. Por pouco, segundo o IBGE, mas há mais de um estudo demonstrando o quanto a autoidentificação para o IBGE embranquece o sujeito em relação a como ele é visto por seus pares e, mais ainda, pela minoria branca que domina o país.

É uma diferença bem grande de horizonte programático que sai dessa diferença demográfica. Uma minoria entre outras almeja, junto com as outras no melhor dos casos e junto com a maioria opressora no pior, representatividade, ser reconhecida, integrar-se. Uma maioria oprimida por uma minoria violenta almeja uma revolução em que tome o poder. O modelo, ao invés de ser o do extermínio indígena no século XX, é o do Apartheid; passamos dos EUA à África do Sul. Não se tem cotas para ter representação em caminhos de busca pessoal da felicidade, mas para dar acesso da maioria ao controle dos recursos nacionais; não se fala em aplainamento, mas em reparação. (A ação afirmativa americana, imitada aqui, como antes dela as dos grandes países da Eurásia, se direciona a minorias.) Se você conseguisse fazer no Brasil, não uma setorial negra dos partidos tradicionais ou grupo de discussão negro no parlamento, mas um partido de libertação negra e mestiça, que fosse visto como o legítimo representante de um anseio legítimo ao protagonismo, os partidos tradicionais é que seriam, todos, secundários - como ocorre na África do Sul.

Não estou dizendo, pra deixar claro, que os brancos antiracistas brasileiros, e muito menos o movimento negro, fazem isso de caso pensado, no interesse dos blankes. Simplesmente, o que acontece é que essa visão é privilegiada pelas disparidades de poder, prestígio, e geração e transmissão de conhecimento acadêmico, tanto a nível nacional quanto global. Global, porque é tanto mais fácil quanto mais prestigioso seguir os ícones culturais, políticos, e acadêmicos americanos do que africanos. Mais fácil porque conhecimento e ativismo, como tudo mais numa sociedade hierarquizada, se movem mais facilmente em linhas verticais do que horizontais. Mais prestigioso porque, igualmente, o prestígio está muito mais associado, salvo casos excepcionais, ao que acontece nas áreas centrais.

A nível nacional, é curioso notar que o centro de poder econômico e acadêmico do país é justamente o lugar em que o modelo de sociedade americano, com diversas minorias dentro de uma sociedade de maioria branca, está mais próximo de se aproximar da verdade. São Paulo tem menos de um terço da sua população de pretos e pardos, e uma proporção de imigrantes de todo canto, mas especialmente da Ásia oriental, literalmente dezenas de vezes maior do que as da maior parte do país. Assim, adaptar a visão americana ao que se passa em SP gera menos dissonância do que geraria mais ao norte, e mesmo do que ao Sul, que também tem uma maioria branca. E as redes sociais, longe de eliminar a importância dos centros, parecem pelo contrário maximizar essa influência.

Não deixa de ser interessante a ideia de um Brasil onde fosse impensável um presidente branco-branco (já que os campesinos dos sertões nortistas, apesar de serem classificados como brancos, são um problema de racismo e preconceito étnico à parte).
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11 Mar 11:03

the blockchain bandwagon

by tomfishburne

A few weeks ago, a publicly traded beverage company called Long Island Iced Tea Corp changed it’s name to Long Blockchain and announced that it was focusing on blockchain technology. Their stock surged 200% on the news.

Last week, Chanticleer Holdings, which owns burger restaurants and is a franchisee of Hooters, said that it was using blockchain for a new customer rewards program across its restaurants. Their stock shot up by 50%. As they put it:

“Use your Merit cryptocurrency mined by eating at Little Big Burger to get a buffalo chicken sandwich at American Burger Co., or trade them with your vegan friend so he can get a veggie burger at BGR. And that’s just the beginning.”

“Just the beginning” is right. Blockchain is suddenly on the radar of business and marketers are being asked, “what’s your blockchain strategy?” Blockchain is the shiny new thing of 2018.

Your Ad Ignored Here
"If marketing kept a diary, this would be it."
- Ann Handley, Chief Content Officer of MarketingProfs
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And as with every shiny new thing, there’s potential, but it gets masked and obscured by all the hype. This is particularly the case with a complicated technology like blockchain, where there’s a lack of understanding of what the shiny new thing even means.

I found an interesting blockchain resource for marketers, called “The CMO Primer for the Blockchain World” by Jeremy Epstein. It’s incredibly bullish and Jeremy himself admits that he may have “drunk too much Kool-Aid”. But it is a handy overview of some of the potential long-term use cases for marketers, including online ad verification, customer data protection, and product tracking. And I found the underlying metaphor of blockchain as a “trust machine” to be a useful lens.

I think marketers have a tendency to get so excited about shiny new things that we can lose sight of the fundamentals. In the long run, if we want to market iced tea and burgers, we can’t stray too far away from the iced tea and burgers.

Here are a couple other cartoons I drew about the shiny new thing:

Shiny Object Syndrome May 2015



The Emperor’s New Marketing Plan
May 2017

11 Mar 10:59

Thy Will Be Dunk

by delfrig

Thy-Will-Be-Dunk

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14 Feb 20:53

Saturday Morning Breakfast Cereal - Browser History

by tech@thehiveworks.com
Adam Victor Brandizzi

"Sometimes, I... I program in weird languages..." *sobs*



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Late at night, he would sneak into the bathroom, turn the volume down, and read Bloomberg.

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14 Feb 17:39

Passo a passo: um pudim de tapioca que nem vai ao fogo!

by Marcelo Katsuki

Para esses dias de bloquinho, nada como um pudim de tapioca para repor a energia depois de cair na folia! E essa receita, que recebi do chef Carlos Ribeiro, é muito prática, nem vai ao fogo! Eu fazia uma versão com leite quente, mas virava um gororoba, rs. Essa é muito melhor. Vem pro bloco do pudim!

 

Disponha 500 gramas de tapioca em flocos em uma tigela.

 

Misture 1/2 litro de leite com 1 vidrinho pequeno de leite de coco e junte à tapioca. Deixe descansar por 2 horas em temperatura ambiente, até a tapioca absorver o líquido.

 

Junte 1 lata de leite condensado, 1 pacote pequeno de coco ralado (120 g), 2 colheres (sopa) de açúcar e misture.

 

Unte uma forma com um pouquinho de óleo e despeje a mistura. Leve à geladeira por 4 horas antes de desenformar.

 

Na hora de servir, finalize com leite condensado e coco ralado. Também vai bem com ameixas em calda, “como um manjar”, conta o chef Carlos Ribeiro, do restaurante Na Cozinha.

03 Feb 22:33

Powerless Placebos

by Scott Alexander

[All things that have been discussed here before, but some people wanted it all in a convenient place]

The most important study on the placebo effect is Hróbjartsson and Gøtzsche’s Is The Placebo Powerless?, updated three years later by a systematic review and seven years later with a Cochrane review. All three looked at studies comparing a real drug, a placebo drug, and no drug (by the third, over 200 such studies) – and, in general, found little benefit of the placebo drug over no drug at all. There were some possible minor placebo effects in a few isolated conditions – mostly pain – but overall H&G concluded that the placebo effect was clinically insignificant. Despite a few half-hearted tries, no one has been able to produce much evidence they’re wrong. This is kind of surprising, since everyone has been obsessing over placebos and saying they’re super-important for the past fifty years.

What happened? Probably placebo effects rode on the coattails of a more important issue, regression to the mean. That is, most sick people get better eventually. This is true both for diseases like colds that naturally go away, and for diseases like depression that come in episodes which remit for a few months or years until the next relapse. People go to the doctor during times of extreme crisis, when they’re most sick. So no matter what happens, most of them will probably get better pretty quickly.

In the very old days, nobody thought of this, so all their experiments were hopelessly confounded. Then people started adding placebo groups, this successfully controlled for not just placebo effect but regression to the mean, and so people noticed their studies were much better. They called the whole thing “placebo effect” when in fact there was no way to tell without further study how much was real placebo effect and how much was just regression to the mean. If we believe H&G, it’s pretty much all just regression to the mean, and placebo was a big red herring.

The rare exceptions are pain and a few other minor conditions. From H&G #3:

We found an effect on pain, SMD -0.28 (95% CI -0.36 to -0.19)); nausea, SMD -0.25 (-0.46 to -0.04)), asthma (-0.35 (-0.70 to -0.01)), and phobia (SMD -0.63 (95% CI -1.17 to -0.08)). The effect on pain was very variable, also among trials with low risk of bias. Four similarly-designed acupuncture trials conducted by an overlapping group of authors reported large effects (SMD -0.68 (-0.85 to -0.50)) whereas three other pain trials reported low or no effect (SMD -0.13 (-0.28 to 0.03)). The pooled effect on nausea was small, but consistent. The effects on phobia and asthma were very uncertain due to high risk of bias.

So the acupuncture trials seem to do pretty well. This probably isn’t because acupuncture works – some experiments have found sham acupuncture works equally well. It could be because acupuncture researchers have flexible research ethics. But Kamper & Williams speculate that acupuncture does well because it’s an optimized placebo. Normal placebos are just some boring little pill that researchers give because it’s the same shape as whatever they really want to give. Acupuncture – assuming that it doesn’t work – has been tailored over thousands of years to be as effective a pain-relieving placebo as possible. Maybe there’s some deep psychological reason why having needles in your skin intuitively feels like the sort of thing that should alleviate pain.

I want to add my own experience here, which is that occasionally I see extraordinary and obvious cases of the placebo effect. I once had a patient who was shaking from head to toe with anxiety tell me she felt completely better the moment she swallowed a pill, before there was any chance she could have absorbed the minutest fraction of it. You’re going to tell me “Oh, sure, but anxiety’s just in your head anyway” – but anxiety was one of the medical conditions that H&G included in their analysis. Plausibly they studied chronic anxiety, and pills are less good chronically than they are at aborting a specific anxiety attack the first time you take them. Or maybe her anxiety was somehow related to a phobia, one of the conditions H&G find some evidence in support of a placebo for. (Really? Phobia but not anxiety? Whatever.)

Surfing Uncertainty had the the best explanation of the placebo effect I’ve seen. Perceiving the world directly at every moment is too computationally intensive, so instead the brain guesses what the the world is like and uses perception to check and correct its guesses. In a high-bandwidth system like vision, guesses are corrected very quickly and you end up very accurate (except for weird things like ignoring when the word “the” is twice in a row, like it’s been several times in this paragraph already without you noticing). In a low-bandwidth system like pain perception, the original guess plays a pretty big role, with real perception only modulating it to a limited degree (consider phantom limb pain, where the brain guesses that an arm that isn’t there hurts, and nothing can convince it otherwise). Well, if you just saw a truck run over your foot, you have a pretty strong guess that you’re having foot pain. And if you just got a bunch of morphine, you have a pretty strong guess that your pain is better. The real sense-data can modulate it in a Bayesian way, but the sense-data is so noisy that it won’t be weighted highly enough to replace the guess completely.

If this is true, placebo should be strongest in subjective perceptions of conditions sent to the brain through low-bandwidth relays. That covers H&G’s pain and nausea. It doesn’t cover asthma and phobias quite as well, though I wonder if “asthma” is measured as subjective sensation of breathing difficulty.

What about depression? My gut would have told me depressed people respond very well to the placebo effect, but H&G say no.

I think that depressed mood may respond well to the placebo effect on a temporary basis – after all, mood seems noisy and low-bandwidth and hard to be sure of in the same way pain and nausea are. But most studies of depression use tests like the HAM-D, which measure the clinical syndrome of depression – things like sleep disturbance, appetite disturbance, and motor disturbance. These seem a lot less susceptible to subjective changes in the way the brain perceives things, so probably HAM-D based studies will show less placebo effect than just asking patients to subjectively assess their mood.