Is sample building an opinion? Short dissertation about “root biases”

Trumpet SoldierRecently a person informed me about a study published on Proceedings of the National Academy of Sciences of the United States of America: Music training alters the course of adolescent auditory development.

THe scientists observed a group of 40 adolescents: 20 of them chose in-school music training. Please wait: I will tell you what other 20 adolescents chose, after.

The study demonstrates “in-school music training changes the course of adolescent brain development. Relative to an active control group that shows the expected wane in subcortical response consistency, adolescents undertaking in-school music training maintained heightened neural consistency throughout high school. The music training group also exhibited earlier emergence of the adult cortical response, suggesting that in-school music accelerates neurodevelopment“. In other words: linguistic and cognitive functions improve more if you study and play an instrument.

The other sub-sample (20 adolescents) chose a military cadet programme.

Okay, I’m an anti-militarist. I could be partial. I seriously disapprove who wants to wear a uniform. But, please, don’t think about my prejudices.

Am I the only one who thinks that if a group chooses to play an instrument and another group chooses to be a military official, some cognitive development are already acting?

Am I the only one who thinks certain samples are biased? I am not speaking about “numbers”. 40 cases multiplied for a long time and several observations, are probably a sufficient sample (answer to people who always ask me “Why do you use sample of about 1000 cases in Italy and China?” or “How can a 1000 cases sample represent 40 million of consumers?”).

But if I take two inhomogeneous population, may I be sure my results do not depend on a root bias?

It could be strange: marketing  survey are sometimes affected by such mistakes.

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