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rules, so that no unfair decision rule can be mined from the transformed data. As
part of this effort, the metrics that specify which records should be changed, how
many records should be changed and how those records should be changed during
data transformation are developed.
There are some assumptions common to all methods in this section. First, we as-
sume the class attribute in the original dataset
DB
to be binary (
e.g.
denying or
granting credit). Second, we obtain the database of
discriminatory
and
redlining
rules as output of a discrimination measurement (discovery) phase based on meas-
ures proposed in Pedreschi
et al.
(2008) and Pedreschi
et al.
(2009a); discrimination
measurement is performed to identify
discriminatory
and
redlining rules
(based on
the work in Chapter 5); then a data transformation phase is needed to transform the
data in order to remove all evidence of direct or indirect discriminatory biases asso-
ciated to
discriminatory
or
redlining
rules. Third, we assume the discriminatory
itemsets (
i.e.
A
) and the non-discriminatory itemsets (
i.e.
D
) to be categorical.
13.4.1 Direct Discrimination Prevention Methods
The proposed solution to prevent direct discrimination is based on the fact that the
dataset of decision rules would be free of direct discrimination if it only contained
PD rules that are
protective
or PD rules that are instances of at least one
non-
redlining (legitimate)
PND rule. Therefore, a suitable data transformation with
minimum information loss should be applied in such a way that each
discrimina-
tory
rule either becomes
protective
or an instance of a
non-redlining
PND rule.
We call the first direct rule protection and the second one rule generalization.
Direct Rule Protection (DRP)
In order to convert each
discriminatory
rule
r': A, B →C
, where
A
is a discriminato-
ry itemset (
A
nDI
s
)
), into a
protec-
tive
rule, two data transformation methods (DTM) could be applied. One method
(DTM 1) changes the discriminatory itemset in some records (
e.g.
gender changed
from male to female in the records with granted credits) and the other method (DTM
2) changes the class item in some records (
e.g.
from grant credit to deny credit in the
records with male gender). Table 13.1 shows the operation of these two methods.
DI
s
) and B is non-discriminatory itemset (B
Table 13.1
Data transformation methods for direct rule protection
Direct Rule Protection
DTM 1 ~
,
→~
⇒
,
→ ~
DTM 2 ~
,
→~
⇒
~
,
→
Table 13.1 shows that in DTM 1 some records supporting rule ~
,
→
~
will
be changed by modifying the value of the discriminatory itemset from ~
A
(Sex=Male) to
A
(Sex=Female) until
discriminatory
rule
r': A, B →C becomes
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