Topics where everything you know is wrong

[astorian]

Well, almost everything I learned about dinosaurs as a kid (that they were stupid and had pea-sized brains, that they were cold-blooded…) has turned out to be wrong.

[astro]

@ultrafilter

Unfortunately there’s no short version, and it gets quickly into some open questions. I wish I had a better explanation for the layperson, but I think it’s going to take the field a while to get there.

It’s mathematics not magic. If the process and formulas used in intro stat and probability classes give correct answers how are they “polite fictions”.

Just give one example of what you mean. What, in any example below, is a polite fiction.
Here’s a basic probability problem

The probability of event A is the number of ways event A can occur divided by the total number of possible outcomes. Let’s take a look at a slight modification of the problem from the top of the page.
Experiment 1: A spinner has 4 equal sectors colored yellow, blue, green and red. After spinning the spinner, what is the probability of landing on each color? spinner
Outcomes: The possible outcomes of this experiment are yellow, blue, green, and red.
Probabilities:
P(yellow) = # of ways to land on yellow = 1
total # of colors 4

P(blue) = # of ways to land on blue = 1
total # of colors 4

P(green) = # of ways to land on green = 1
total # of colors 4

P(red) = # of ways to land on red = 1
total # of colors 4

---

Experiment 2: A single 6-sided die is rolled. What is the probability of each outcome? What is the probability of rolling an even number? of rolling an odd number? dice

Outcomes: The possible outcomes of this experiment are 1, 2, 3, 4, 5 and 6.
Probabilities:

P(1) = # of ways to roll a 1 = 1
total # of sides 6

P(2) = # of ways to roll a 2 = 1
total # of sides 6

P(3) = # of ways to roll a 3 = 1
total # of sides 6

P(4) = # of ways to roll a 4 = 1
total # of sides 6

P(5) = # of ways to roll a 5 = 1
total # of sides 6

P(6) = # of ways to roll a 6 = 1
total # of sides 6

P(even) = # ways to roll an even number = 3 = 1
total # of sides 6 2

P(odd) = # ways to roll an odd number = 3 = 1
total # of sides 6 2

Experiment 2 illustrates the difference between an outcome and an event. A single outcome of this experiment is rolling a 1, or rolling a 2, or rolling a 3, etc. Rolling an even number (2, 4 or 6) is an event, and rolling an odd number (1, 3 or 5) is also an event.
In Experiment 1 the probability of each outcome is always the same. The probability of landing on each color of the spinner is always one fourth. In Experiment 2, the probability of rolling each number on the die is always one sixth. In both of these experiments, the outcomes are equally likely to occur. Let’s look at an experiment in which the outcomes are not equally likely.
Experiment 3: A glass jar contains 6 red, 5 green, 8 blue and 3 yellow marbles. If a single marble is chosen at random from the jar, what is the probability of choosing a red marble? a green marble? a blue marble? a yellow marble? [IMAGE]
Outcomes: The possible outcomes of this experiment are red, green, blue and yellow.
Probabilities:
P(red) = # of ways to choose red = 6 = 3
total # of marbles 22 11

P(green) = # of ways to choose green = 5
total # of marbles 22

P(blue) = # of ways to choose blue = 8 = 4
total # of marbles 22 11

P(yellow) = # of ways to choose yellow = 3
total # of marbles 22

The outcomes in this experiment are not equally likely to occur. You are more likely to choose a blue marble than any other color. You are least likely to choose a yellow marble.

Experiment 4: Choose a number at random from 1 to 5. What is the probability of each outcome? What is the probability that the number chosen is even? What is the probability that the number chosen is odd?
Outcomes: The possible outcomes of this experiment are 1, 2, 3, 4 and 5.
Probabilities:
P(1) = # of ways to choose a 1 = 1
total # of numbers 5

P(2) = # of ways to choose a 2 = 1
total # of numbers 5

P(3) = # of ways to choose a 3 = 1
total # of numbers 5

P(4) = # of ways to choose a 4 = 1
total # of numbers 5

P(5) = # of ways to choose a 5 = 1
total # of numbers 5

P(even) = # of ways to choose an even number = 2
total # of numbers 5

P(odd) = # of ways to choose an odd number = 3
total # of numbers 5

The outcomes 1, 2, 3, 4 and 5 are equally likely to occur as a result of this experiment. However, the events even and odd are not equally likely to occur, since there are 3 odd numbers and only 2 even numbers from 1 to 5.

Summary: The probability of an event is the measure of the chance that the event will occur as a result of an experiment. The probability of an event A is the number of ways event A can occur divided by the total number of possible outcomes. The probability of an event A, symbolized by P(A), is a number between 0 and 1, inclusive, that measures the likelihood of an event in the following way: �If P(A) > P(B) then event A is more likely to occur than event B.
�If P(A) = P(B) then events A and B are equally likely to occur

[CookingWithGas]

@Mathematics

Hmm, does chiropractic count?

Until a few years ago, I thought chiropractors were just “back doctors”, that the spine really does need to be realigned periodically, et cetera. Pretty much everything about that is wrong, but I think it’s a common belief around here.

I am curious as to what you learned a few years ago. My personal belief is that chiropractic is the equivalent of making you feel good for a while after a nice massage.

[Chronos]

astro, none of that is polite fictions, but then, none of it is really statistics, either. Basic probability is certainly a component of statistics, but that’s all generally taken for granted by the time you’re taking a statistics course. I think that ultrafilter is referring more to statements like “If the confidence level for rejecting the null hypothesis is over 95% (or maybe 90%, or 99%, depending on whom you ask), you should reject the null hypothesis”. Which, really, is only true if the prior you attached to the null hypothesis was less than .95 (or .9 or .99). But students in intro stats classes usually aren’t even taught about priors at all.

[Mathematics]

@CookingWithGas

I am curious as to what you learned a few years ago. My personal belief is that chiropractic is the equivalent of making you feel good for a while after a nice massage.

As far as I know, the perception of chiropractic varies by location. But where I’m from (Missouri), most people think that chiropractors are something akin to physical therapists or actual doctors.

*Kid diagnosed with scoliosis? Take him to the chiropractor! They’ll get that spine right back in shape.

Having morning sickness? Your spine is maligned! I know of a great chiropractor who will fix that up.

Did you get tackled at football practice and pass out? The friendly neighborhood chiropractor will know what to do.
*
Et cetera. Of course, it turns out that they absolutely are not doctors and can’t fix anything that people around here go to them for. I was shocked to find this all out.

[Really_Not_All_That_Bright]

@Mathematics

Hmm, does chiropractic count?

Until a few years ago, I thought chiropractors were just “back doctors”, that the spine really does need to be realigned periodically, et cetera. Pretty much everything about that is wrong, but I think it’s a common belief around here.

Chiropractors can broadly be pushed into two groups. The first group think spinal realignment can cure everything, because all symptoms are caused by “subluxations”. Got cancer? It’s because one of your joints is misaligned. These people, obviously, are cranks or frauds. D. D. Palmer, the guy who made up the field, was one of these cranks.

The second group is largely evidence-based, and most concedes that at best they might be able to cure your low back pain.

[Miss_Woodhouse]

I’ll go with dinosaurs too. I pictured most of them as the big monsters that look like over grown reptiles. In fact, the vast majority of them were smaller than the average man, with a large number of them being the size of a dog or smaller. Common thought these days also points to a lot more of them having feathers than we ever thought before. Way different than what I was taught in school.

Eating unhealthy food is cheaper. Nope. cooking from scratch is almost always cheaper than prepackaged crap. The problem comes when people start talking about healthy foods only being organic produce and talk about more expensive produce at that (how everyone should be eating blueberries all the time and less common veggies.) Those things are fun, but they aren’t necessary to be healthy. Organic eating is a choice and eating fresh foods is always better even when you can’t afford organic. Common fruits and veggies and fresh home made from scratch foods are cheaper than the box. It’s one of the main reasons I rarely serve prepacked crap to my family. (well that and it tastes ten times better.)

[Wesley_Clark]

Most Americans have no idea what the government spends money on. If you ask them many will say ‘foreign aid and welfare for poor people’ are some of our biggest expenses. As it is, foreign (non-military) aid is a small fraction of 1% of the federal budget (something like 0.2%), not the 20-25% most people assume.

Plus you get people who think eliminating things like the NEA or PBS will fix the deficit. About 70-90% of government spending (on the federal, state, county & city combined) level is spent on about 4 things. Security (military, police, fire, prisons, etc); wealth transfers (social security for the elderly, disabled and orphans, AFDC, etc); education and health care. If people want to affect government spending they have to cut from those 4 areas.

People also don’t know what the wealth distribution in the US is, people think the gini coefficient is much lower than it is.

Here is another one (I don’t know if people still believe it). If you ask an undercover cop if he is a cop, he has to tell you the truth. That isn’t true. If you suspect someone is an undercover cop then ask them to commit a minor crime (or to have sex with a hooker). That probably works better.

[Ambivalid]

@Wesley_Clark

Most Americans have no idea what the government spends money on. If you ask them many will say ‘foreign aid and welfare for poor people’ are some of our biggest expenses. As it is, foreign (non-military) aid is a small fraction of 1% of the federal budget (something like 0.2%), not the 20-25% most people assume. {snip}

Plus you get people who think eliminating things like the NEA or PBS will fix the deficit. {snip}

Here is another one. If you ask an undercover cop if he is a cop, he has to tell you the truth.

I don’t think most Americans actually believe these things. Especially not the second two examples you give; I think only truly intentionally misinformed ideologues would believe that shit about the NEA or PBS. And only dumb hookers believe that last one.

[panache45]

@Der_Trihs

The idea that evolution has a direction; such as the idea that evolution means everything getting “better”, and that there’s some end goal to it. The related idea that we are “more evolved” than other animals, and that predators are more evolved than herbivores or for that matter parasites/plants.

And the idea that every single aspect of our lives is the result of rigorous evolutionary forces, that even the tiniest characteristics must have a justification and purpose, in terms of survival of the species.

We contain a whole lot of stuff that’s fairly arbitrary and pointless.