I think it is somewhat unrealistic to expect individual digit ratios to be accurate to three significant figures (although I understand that two significant figures might be too crude a measure to show effects of smaller size). One can hope that the errors are symmetric and it doesn’t matter.
I don’t think it’s going to matter very much. 3 digits after the dot, with the understanding that the third digit is probably not very good, but the second probably is pretty good.
Suppose the actual length of a person’s index finger is 80.5 mm and the actual length of his/her ring finger is 83.5 mm. Then the 2D:4D ratio is 0.964. A measurement error of 0.5 mm is very easy to make, e.g. due to inaccuracy of a photocopier, inaccuracy of a ruler, inexactness of where a finger joins the hand (and even if it wasn’t a vague concept it would still be a problem to pinpoint the precise location of it with a great accuracy) and even differences in muscle tension in fingers at the particular moment of placing a hand in a photocopier. If a person measures his/her index finger as being 80 mm long (0.5 mm shorter) and her/his ring finger as being 84 mm long (0.5 mm longer), then they would obtain 2D:4D ratio of 0.952. Whereas if the length of the index finger is measured to be 81 mm, and the length of the ring finger is 83 mm, then 2D:4D ratio is 0.976. Therefore, the first digit after the decimal point does not vary that much (in the vast majority of all cases it is 9), the third one is basically noise, and even the second one is not that reliable (in an individual case). However, that might still be enough to notice some interesting correlations and if the errors are symmetric it might not even matter that much when all data will be aggregated.
For me its not even the second digit. Even left and right hand differ significantly. Copire doesn’t make things really better (OK, the copier quality was low, much too dark).
This is why a scanner might make sense. Even 300 DPI is less than 0.1mm resolution, so just scan it in and measure with an electronic ruler in your image-editing software of choice.
There’s no point in measuring something more precisely than the thing itself exists. Which pixel “is” the base of the finger?
Has anyone tried repeating the measurement, following the same procedure each time? Do this on occasions at least a day apart, to avoid unconsciously imitating the second time exactly what you did the first time. I have. Reproducibility was no better than 1mm, and pretty much independent between fingers.
You could also try under different conditions, e.g. when your hands are cold and when they’re warm, when you’ve just been exerting them heavily and when you haven’t, etc.
I doubt that digit ratio exists as an entity to better than 1 or 2% accuracy.
Done.
I think it is somewhat unrealistic to expect individual digit ratios to be accurate to three significant figures (although I understand that two significant figures might be too crude a measure to show effects of smaller size). One can hope that the errors are symmetric and it doesn’t matter.
I don’t think it’s going to matter very much. 3 digits after the dot, with the understanding that the third digit is probably not very good, but the second probably is pretty good.
Suppose the actual length of a person’s index finger is 80.5 mm and the actual length of his/her ring finger is 83.5 mm. Then the 2D:4D ratio is 0.964. A measurement error of 0.5 mm is very easy to make, e.g. due to inaccuracy of a photocopier, inaccuracy of a ruler, inexactness of where a finger joins the hand (and even if it wasn’t a vague concept it would still be a problem to pinpoint the precise location of it with a great accuracy) and even differences in muscle tension in fingers at the particular moment of placing a hand in a photocopier. If a person measures his/her index finger as being 80 mm long (0.5 mm shorter) and her/his ring finger as being 84 mm long (0.5 mm longer), then they would obtain 2D:4D ratio of 0.952. Whereas if the length of the index finger is measured to be 81 mm, and the length of the ring finger is 83 mm, then 2D:4D ratio is 0.976. Therefore, the first digit after the decimal point does not vary that much (in the vast majority of all cases it is 9), the third one is basically noise, and even the second one is not that reliable (in an individual case). However, that might still be enough to notice some interesting correlations and if the errors are symmetric it might not even matter that much when all data will be aggregated.
For me its not even the second digit. Even left and right hand differ significantly. Copire doesn’t make things really better (OK, the copier quality was low, much too dark).
Agreed. Most rulers don’t give measurements more precise than millimeters.
This is why a scanner might make sense. Even 300 DPI is less than 0.1mm resolution, so just scan it in and measure with an electronic ruler in your image-editing software of choice.
There’s no point in measuring something more precisely than the thing itself exists. Which pixel “is” the base of the finger?
Has anyone tried repeating the measurement, following the same procedure each time? Do this on occasions at least a day apart, to avoid unconsciously imitating the second time exactly what you did the first time. I have. Reproducibility was no better than 1mm, and pretty much independent between fingers.
You could also try under different conditions, e.g. when your hands are cold and when they’re warm, when you’ve just been exerting them heavily and when you haven’t, etc.
I doubt that digit ratio exists as an entity to better than 1 or 2% accuracy.
I suspect it does, but you need to be a lot more precise with your instructions than Yvain was in this case.