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10 is ok for measuring a single variable (although even then, you probably want something like 30, even in the social sciences). But for faces, it is possible

by azakai 13y ago

10 is ok for measuring a single variable (although even then, you probably want something like 30, even in the social sciences). But for faces, it is possible that there are large numbers of relevant variables (various features of the eyes, nose, etc. can all vary separately). That increases the sample size you need to get decent results.

fleitz 13y ago
You're allowed to reuse the same sample for multiple variables, pollsters do it all the time, they'll phone one person and ask them 10 different questions. The fact that you're measuring faces as opposed to political leanings does not affect the underlying statistical methods. Confounding variables only come into play when you're doing regressions, and/or trying to prove causation. Since they aren't attempting to explain why the faces look like this there aren't any confounding variables.
- graycat 13y ago
  Thanks for raising the level of discourse by several notches!
- azakai 13y ago
  That pollsters do something does not make it valid! ;) Yes, they do ask dozens of questions of a small number of people. But this is also mathematically dubious. If you do multiple random samples, the chance at least one is way off increases. If you have a 95% chance of being close to correct on your small sample, and you do 20 samples, it is quite likely you are wrong on at least 1 of them. My claim is that (1) there is a very large number of relevant facial features for the goal of the survey (find the "average" face), and (2) that being wrong on even a small number of them is significant. My basis for both is a combination of intuition and that we know humans are extremely good at perceiving faces and subtle facial differences. There are parts of the brain that are apparently adapted specifically to facial recognition, and disorders where facial recognition is impaired but nothing else, for example.

by azakai 13y ago

fleitz 13y ago

You're allowed to reuse the same sample for multiple variables, pollsters do it all the time, they'll phone one person and ask them 10 different questions. The fact that you're measuring faces as opposed to political leanings does not affect the underlying statistical methods. Confounding variables only come into play when you're doing regressions, and/or trying to prove causation. Since they aren't attempting to explain why the faces look like this there aren't any confounding variables.

graycat 13y ago
Thanks for raising the level of discourse by several notches!
azakai 13y ago
That pollsters do something does not make it valid! ;) Yes, they do ask dozens of questions of a small number of people. But this is also mathematically dubious. If you do multiple random samples, the chance at least one is way off increases. If you have a 95% chance of being close to correct on your small sample, and you do 20 samples, it is quite likely you are wrong on at least 1 of them. My claim is that (1) there is a very large number of relevant facial features for the goal of the survey (find the "average" face), and (2) that being wrong on even a small number of them is significant. My basis for both is a combination of intuition and that we know humans are extremely good at perceiving faces and subtle facial differences. There are parts of the brain that are apparently adapted specifically to facial recognition, and disorders where facial recognition is impaired but nothing else, for example.