Postgres data correlation problem

gistfile1.pl

use strict;
use warnings;

use DBI;
my $dbh = DBI->connect('dbi:Pg:dbname=test', 'postgres', undef, { RaiseError => 1 });

$dbh->do(q{DROP TABLE IF EXISTS test});
$dbh->do(q{
    CREATE TABLE test (
        id INT NOT NULL PRIMARY KEY,
        ColX INT NOT NULL
    )
});

my $total = 1000;

my $sth = $dbh->prepare('INSERT INTO test VALUES (?, ?)');
for ( my $i = 1; $i < $total; $i++ ) {
    my $x = $i;
    if ( rand(1) >= 0.95 ) {
        $x = int(rand($total)) + 1;
    }
    $sth->execute( $i, $x);
}

use Data::Dumper;
$Data::Dumper::Indent = 1;

$dbh->do(q{CREATE INDEX T1 ON test(ColX);});
$dbh->do(q{CREATE INDEX T2 ON test(id, ColX);});
#$dbh->do(q{ALTER TABLE test ALTER COLUMN ColX SET STATISTICS 0});
$dbh->do(q{ANALYZE VERBOSE test});

print Dumper $dbh->selectall_arrayref(
    q{SELECT * FROM pg_stats WHERE tablename = 'test'},
    {Slice => {} }
);

print Dumper $dbh->selectall_arrayref(
    q{EXPLAIN ANALYZE SELECT * FROM test WHERE id = ColX},
    {Slice => {} }
);