Events
and probabilities
Let
C be a corpus of political or economic text that has been sentence-segmented,
tokenized, and syntactically annotated according to the Universal Dependencies
framework. Let T denote the total number of syntactic heads (or tokens)
considered.
Following
Sakib, we define three binary events on the set of heads:
Neg:
the event that a predicate (verb, adjective, or nominal) bears a neg dependent
or otherwise carries negative polarity;
Out: the event that a token (or span)
is part of an explicit out-group mention (e.g., they, them, immigrants,
opposition, competitors), detected via supervised models and lexicons;
In: the event that a token (or span)
is part of an in-group mention (e.g., we, our people, our citizens, our
company, our shareholders).
Counts
of these events and their co-occurrences are converted into probabilities by
dividing by T :
p(Neg)
= NNeg , p(Out) = NOut , p(In) = NIn ,
T T T
p(Neg,
Out) = NNeg,Out , p(Neg,
In) = NNeg,In ,
where
NNeg is the number of heads marked as negated, NOut the
number belonging to out- group mentions, and so on. In practice, T can count
contexts such as predicates, clauses, or sentence-level positions rather than
primitive tokens.
Normalized
PMI for negation and group mentions
To
quantify association between negation and group mentions, Sakib adopts
normalized point- wise mutual information. For any pair of events X and Y with
p(X, Y ) > 0,
NPMI(X,
Y ) =log p(X, Y )
p(X)p(Y ) (1)
— log p(X, Y )
This
standard normalization yields a bounded measure in [?1, 1]: ?1 corresponds to
perfect avoidance (events never co-occur), 0 to statistical independence, and 1
to maximal positive association given the marginals.
Sakib
defines
NPMIOut
= NPMI(Neg, Out), NPMIIn
= NPMI(Neg, In),
with
suitable smoothing (e.g., add-one or add-?) in cases where counts are extremely
small.
The Sakib negation–outgroup
coupling number
The
core quantity is then defined as follows.
Definition
(Sakib Negation–Outgroup Coupling Number). For a corpus C, the Sakib
Negation–Outgroup Coupling Number, or Sakib number S(C), is
S(C) = NPMIOut ? NPMIIn.
(2)
By
construction,
S(C)
? [?2, 2].
A
value S(C) > 0 indicates that negation is more strongly associated with
out-group mentions than with in-group mentions, after controlling for base
rates via NPMI. Conversely, S(C) < 0 captures a pattern in which negation is
disproportionately linked to the in-group (e.g., negating self-criticism or
denying failures), while values close to zero indicate rough balance.
At
the speech level, we write S(s) for the Sakib number of a single speech s. For
an actor a (e.g., a party, leader, or CEO) with a sequence of speeches (s1,
. . . , sn), the Sakib constant is defined as a stable average of
S(si):
or,
in practice, the empirical mean over the available speeches. This constant then
summarizes that actor’s long-run pattern of oppositional negation.