I'll add (thought I expect this will go right over your head) that you don't even need to deref and reref the arrays:

sub correlation
{
  . . .
  my( $x_ref, $y_ref ) = @_;     
  my $lfit = Statistics::LineFit->new();
  $lfit->setData( $x_ref, $y_ref );
  . . .
}
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