Evidence based reasoning: prior beliefs

Our belief, before any (new) evidence comes our way, is called a prior belief or simply prior.

Which ones of the statements describe a prior? Select all that apply.

• After running the marathon twice, I now know how hard it is.

• I don't know anyone that has run a marathon, but I assume it takes 3 months to prepare.

• Shrimp? I don't know how much fat there is in that, but let's say it's the same as in crab, then about 1 g of fat per 100 g of shrimp.

• Fat in shrimp? I don't know.. Let's look on that package, oh, it says here about 3 g per 100 g of shrimp.

You want to choose a university soon and would like to know which one has the most challenging study programs.

What would be a well-chosen prior? More than one can apply.

• I don't have any data so far, so I'll assume they're all about equally challenging until I get more information.

• The LMU is the largest in Germany, which probably makes it the most challenging.

• Heidelberg is Germany's oldest university, which probably makes it the most challenging.

• There's really nothing you can say about this without solid data.

You'd like to know how much you have to spend on clothes next year. You've never recorded how much you spent on clothes before.

What would be a well-chosen prior for clothing-expenses over the full year? Select all that apply.

• What an average German kid my age spends each year.

• The same my brother/sister, who's the same gender and age as me, spent this year.

• Calculate how much my favorite style&fashion blogger, who's style matches my own, spent on clothes last year.

• In three weeks I'll go shopping, and write down how much I spent. Then, there are 52 weeks in the year, so multiply what I spent by 52.

You'd like to estimate how many taxis are available at the Frankfurt airport.

What would be a well-chosen prior? More than one can apply.

• The number of taxis at the Regensburg airport

• Assume every person uses a taxi, and look up the number of people that use the Frankfurt airport

• You compute how many taxis per person at the Munich airport, and multiply that with the number of travelers in Frankfurt.

• You look up the number of specially designated taxi parking places, and assume about 50% of them are occupied.

As part of a school Spendenaktion, you have to choose a cause. In order to choose a good cause, you'd like to know which disease has the most victims in Germany.

What would be a well-chosen prior? More than one can apply.

• I look up which diseases have been getting the most media coverage this year.

• I ask my uncle, who had to go to a special hospital very often because he had a rare disease himself.

• I think of all the people that got ill in my family, and select the one that had the most victims.

• disease X, which is very deadly (almost everyone was killed in a village)

Rank these priors by how likely you think they are. Until I get any concrete evidence on them, I'll assume that fish in the South China Sea are very similar to 1: aquarium fish from Sweden, 2: Chinese aquarium fish, 3: wild fish from the North Sea, 4: wild fish from Morocco (which is at a similar latitude). Write your answer as: 4,3,2,1 (For this question and the next ones, there is more than one 'right' answer)

Rank these priors by how likely you think they are. Until I get any concrete evidence on them, I'll assume that people working for large banks are 1: normal people, but that are morally corrupted, 2: basically normal people, 3: like the character in "American Psycho", greedy, violent psychopaths, 4: psychopaths