Later in the article, the authors identify the following costs as being associated with losing a good developer:

• The direct outlays to the firm incurred by the replacement process: recruiting, hiring, training, and socializing new employees including the extra effort by supervisors and coworkers to integrate them;
• The indirect costs and losses that relate to interruptions in production, sales, and the delivery of goods and services to customers; and
• The financial value of the estimated effect on performance as a result of the drop in morale of the remaining work force following on dysfunctional turnover.

Based on these costs, the authors developed the following formula that allowed them quantify the cost associated with the lost of a top performer:

$cost_associated_with_lost = 
  ($cost_differential + 
   $cost_of_acquiring_new_employee + 
   $cost_of_training_new_employee +
   $cost_paid_to_integrate_new_employee +
   $cost_of_excess_overtime_payment_to_compensate_temporary_performanc
+e_downfall  +
   $cost_of_loss_of_production_or_loss_of_customers +
   $monetary_value_of_loss_of_morale_of_remaining_employees)
   * (1 + $turnover_rate_of_newcomer_to_organization)
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with $cost_differential being the cost differentials during the entire period (in years) in which the departing employee was expected to perform efficiently if he or she did not leave. This cost can be computed by:

foreach (1..$total_number_of_years) {
    $cost_differential += ( $annual_remuneration_of_new_employee - $an
+nual_remuneration_of_person_leaving ) /  (1 + $interest_rate_paid_by_
+employer / 100)**$_
}
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In the article, the authors provide an example using probable numerical figures based on their experience as consultants (the values should be adjusting according to the particular industry in which the cost is computed). The values they used were:

$total_number_of_years = 10;
$interest_rate_paid_by_employer = 10;
$annual_remuneration_of_person_leaving = 64800;
$annual_remuneration_of_new_employee = 60380;
$cost_of_acquiring_new_employee = 3150;
$cost_of_training_new_employee = 10000;
$cost_paid_to_integrate_new_employee = 48600;
$cost_of_excess_overtime_payment_to_compensate_temporary_performance_d
+ownfall   = 1000;
$cost_of_loss_of_production_or_loss_of_customers =  55440;
$monetary_value_of_loss_of_morale_of_remaining_employees = 3000;
$turnover_rate_of_newcomer_to_organization = 0.1;
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with those values, $cost_associated_with_lost would be 103434. See code below

#!/usr/bin/perl
use warnings;
use strict;

my $line = <DATA>;
chomp ($line);
my @data = split /\s+/, $line;

my $total_number_of_years = shift( @data );
my $interest_rate_paid_by_employer = shift( @data );
my $annual_remuneration_of_person_leaving = shift( @data );
my $annual_remuneration_of_new_employee = shift( @data );

my $cost_differential = 0;

foreach (1..$total_number_of_years) {
    $cost_differential += ( $annual_remuneration_of_new_employee - $an
+nual_remuneration_of_person_leaving ) /  (1 + $interest_rate_paid_by_
+employer / 100)**$_
}

my $turnover_rate_of_newcomer_to_organization = pop( @data );
my $cost_of_losing_good_people = 0;

foreach (@data) {
    $cost_of_losing_good_people += $_;
}

$cost_of_losing_good_people += $cost_differential;
$cost_of_losing_good_people *= (1 + $turnover_rate_of_newcomer_to_orga
+nization);

$cost_of_losing_good_people = int( $cost_of_losing_good_people );
print "Cost of Losing Good People = \$$cost_of_losing_good_people\n";

__DATA__
10 10 64800 60380 3150 10000 48600 1000 55440 3000 0.1
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