The flaws that are inherent in studies of this type include the fact that they are done on psychology students, a unique and self-selected group who may not represent the general population very well, and they are done with a questionnaire, which invites inaccurate answers. I wouldn't call this junk science but the methodology means that it has limited value.
Contrast this with research by Jerome Kagan and others showing a very strong correlation between fetal heart rate and subsequent fearfulness and introversion. In other words, these traits are genetic, inborn.
Skilled therapists can help people manage such fears, but there is little research to guide treatment
Translation; they take money for dispensing worthless advice. They're snake oil peddlers.
You can't teach someone to be tall, strong, smart, or good looking...and you almost certainly can't teach them to be brave either.
And then there's the kind
that puts on a diaper and
drives across country . . .