my @institutions = qw|hospital1 hospital2|;
my %seen;
$seen{$_}++ foreach @institutions;

if (!defined $institution) {
    $institution_table{"unaffiliated"} ++;
} elsif (exists $seen{lc $institution}) {
    $institution_table{lc $institution} ++;
} else {
    $institution_table{"other"} ++;
}