I am having trouble concording “a low signal:noise ratio biases the effects, often towards zero” with the result in the final section, where you say
“the genetic correlation has ended up much bigger than the environmental correlation. This happened due to the measurement error; if it was not for the measurement error, they would be of similar magnitudes.”
In the second statement, the noise (measurement error) was high, so there’s a low signal:noise ratio—is that right? If so, doesn’t the first statement suggest the genetic correlation should be biased towards zero, instead of being inflated?
The measurement error is assumed to be independent between the twins, which puts it in the “non-shared environment” (E) bucket. So the E-correlation is biased towards zero while the genetic (A) correlation is fine.
I am having trouble concording “a low signal:noise ratio biases the effects, often towards zero” with the result in the final section, where you say
“the genetic correlation has ended up much bigger than the environmental correlation. This happened due to the measurement error; if it was not for the measurement error, they would be of similar magnitudes.”
In the second statement, the noise (measurement error) was high, so there’s a low signal:noise ratio—is that right? If so, doesn’t the first statement suggest the genetic correlation should be biased towards zero, instead of being inflated?
The measurement error is assumed to be independent between the twins, which puts it in the “non-shared environment” (E) bucket. So the E-correlation is biased towards zero while the genetic (A) correlation is fine.