Wednesday, January 02, 2013

GIGO (Garbage In Gospel Out)

Other terms and/or related concepts

False premise; hidden premise; circular reasoning; begging the question; simple-minded certitude


The advocate is certain their belief is true, even though the data, evidence or underlying theory or assumption on which the belief is based is demonstrably flawed or unsubstantiated. Or rather, the advocate treats conclusions leading from some flawed data, unsubstantiated evidence, unfounded assumption or baseless theory, as gospel.


Roz Well is having an online discussion at, explaining to her friend Joan Mack why she knows there is “life out there”.

She says:
The Drake equation proves it. It states that: N = R* fp ne fl fi fc L, where N is the number of civilizations in our galaxy with which we might hope to be able to communicate; and R* is the average rate of star formation in our galaxy, fp is the fraction of those stars that have planets, ne is the average number of planets that can potentially support life per star that has planets, fl is the fraction of the above that actually go on to develop life at some point, fi is the fraction of the above that actually go on to develop intelligent life, fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space, L is the length of time such civilizations release detectable signals into space.

When you substitute all the right values into it, you get an answer of 5000! That means there are at least 5000 civilisations in our galaxy that we can communicate with. Imagine how many more there are in the entire universe!
Joan Mack is a well respected psychologist and as such has an understanding of fallacies. She types back:
Look, you can get whatever answer you want with the Drake equation – so long as you pick the input values that give you the answer you want. GIGO! I am happy to accept the equation itself as valid. But this doesn't mean we can get any useful information from it.
Roz replies: "So, are you saying you don’t believe?"

“Of course not", replies Joan. "Just that the Drake equation is not a good argument." She goes on to explain:
In my practice as a psychologist I have specialised in treating patients who have been abducted and fiddled with by aliens. Now that's conclusive proof. Unfortunately the rules of doctor-patient confidentially prohibit me from backing up this claim with any specific evidence – other than the cash-money I'll no doubt make when my book comes out. I’ve also been very successful in treating my patients with my anti-alien mind control helmet. It’s made from til foil!
"Cool.” Types Roz. “Where can I order mine?"


GIGO is a reasonably well known principle: Garbage In, Garbage Out. It was originally coined in a computer science environment to point out that an algorithm will process all data, no matter the quality, and give an answer. Thus, if junk data is fed into an algorithm, a junk answer will be the result. (The quality of one’s evidence is only as good as the weakest bit).

From this principle we can derive the “GIGO fallacy”. In this case GIGO stands for: Garbage In = Gospel Out. Again, in the computer science context, it refers to the blind belief in the answer obtained from computers. The use here is intended to be broader, and refers to the blind acceptance of a result of a process being a fact because of a simple-minded belief in the process. This can be for obvious examples such as the Drake equation above (which should be viewed as a fun thought experiment) to more important processes.

In the example above, Joan is correct in her overall dismissal of any value that is determined by the Drake equation. The logic of the equation is sound enough. But if the input values are essentially guesses, the multiplication of uncertainties becomes so large that it makes any calculation worthless.

Let's consider another example. We can calculate the strength of the Earth’s gravitational field (g) at the surface, using the equation: g = GM/r2. Where G = the universal gravitational constant, M = the mass of the Earth, and r = the radius of the Earth.

If we didn’t know the actual values for G, M and r, we could just choose numbers that "feel" right (i.e., based on our best guess). If enough people have enough guesses, we might even chance upon the right answer (9.8 N/kg), because the equation works (though this would be extremely unlikely in itself). However, we’d never know, because we were just guessing at the values we assigned to the input variables. Even if the equation is right, it is useless without the correct input data.

The problem with the Drake equation, why it falls into the GIGO category, lies with the parameters. There is no way to tell if the values we assign to the input parameters are garbage or not. Given the impossibility of assigning justifiable values to them, we can treat them all as garbage (though we can argue about which values stink more). All probabilities found using the Drake equation are therefore, to some extent, invalid (even if you accidentally guessed the right values). Some are more reasonable than others, but all the answers the Drake equation spits out still suffer from GIGO.

More generally, if the data, evidence or underlying theory used as the basis of a claim is flawed, then the claim and all conclusions based on it should be treated with great skepticism. (The claim and any conclusions may or may not be true; however there is simply no reasonable evidence either way.)

Statements such as "Tried and convicted by a jury of peers", or “It’s been peer reviewed”, could potentially be GIGO. If the legal process in a court case allows for flawed evidence or biased jury selection then we might not have confidence in the jury's verdict. If the peer review was by "peers" in a journal whose editorial standards poor, we might not have confidence in the conclusions of the papers in the journal (c.f. the Sokal affair and the journal Social Text).

Whilst we should be alert for GIGO, we need to also note the potential for a Red Flag Faux Pas. Using the examples in the preceding paragraph again, as a rule of thumb the criminal justice system and peer review can be trusted. Therefore if one wants to claim GIGO legitimately, one needs to provide evidence for it. Otherwise a claim of GIGO might simply be a "conversation ender".