if (55 < $age && $age <= 60) ...

##</code><code>##

foreach (keys %insitution_table)
{
     $institution_table{$_}{ages}[$age/5]++;
}

##</code><code>##

my $sample = $insitution_table{$_}{ages}[60/5];

##</code><code>##

my %valid_institutions = map { $_ => $_ } (
      $hospital1,
      $hospital2,
);

# ...

my $key = $institution
          && ($valid_institution{lc($institution)} || "other")
          || "unaffiliated";

$institution_table{$key}{count}++;

##</code><code>##

my %foo = map { $_ => 1 } qw[ foo bar baz ];

my $foo = 'foo';
print "\$foo is in the list\n" if ($foo{$foo});

##</code><code>##

... $valid_institution{lc($institution)} || ...

##</code><code>##

... $valid_institution{lc($institution)} && lc($institution) ||  ...