Thank you for those references which essentially confirm what I...

Thank you for those references which essentially confirm what I suggested, ie that there is no specific biochemical test that will show the presence of depression.

There are many "may be"s, "seems to suggest".
"current evidence suggests....." etc. but nothing definitive.

So for the apparently conclusive statement that 'depression is caused by a chemical imbalance' to be repeated with such assurance by so many seems inappropriate to me.

I have no doubt, however, it will continue, and scant recognition will be afforded the simple reality that life is often hard and sadness is inevitable.