function get_churn_by_year( $year = false ) {

    if ( ! isset( $_GET['churn'] ) || ! is_admin() ) {
        return;
    }

    $year            = 2019;
    $year_to_compare = $year - 1;

    for ( $i = 0; $i < 4; $i++ ) {

        $args = array(
            'number'     => -1,
            'date_query' => array(
                array(
                    'year' => $year_to_compare,
                ),
            ),
        );

        $customers = new EDD_Customer_Query( $args );

        $total   = count( $customers->items );
        $renewed = 0;

        foreach ( $customers->items as $customer ) {

            $args = array(
                'customer'   => $customer->id,
                'year'       => $year,
                'meta_key'   => '_edd_sl_is_renewal',
                'meta_value' => true,
            );

            $payments = new EDD_Payments_Query( $args );

            $payments = $payments->get_payments();

            if ( ! empty( $payments ) ) {
                $renewed++;
            }
        }

        error_log( 'YEAR ' . $year_to_compare . ' vs ' . $year );
        error_log( 'Total customers: ' . $total . '. Renewed in ' . $year . ': ' . $renewed );
        error_log( 'Renewal rate: ' . ( $renewed / $total ) * 100 . '%' );

        $year_to_compare--;

    }

}

add_action( 'init', 'get_churn_by_year' );