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28 UNIT I Evolution of Nursing Theories

the truth of the antecedent. Rather, the assertion is case, (1) the consequent never occurs in the absence
made that if the antecedent is true, then the conse- of the antecedent and (2) the consequent always
quent is true (Giere, 1979). In addition, no assertion occurs when the antecedent occurs (Giere, 1979). It
appears in the statement explaining why the anteced- should be noted that not all conditional statements
ent is related to the consequent. In symbolic notation are causal. For example, “If this month is November,
form, the statements may be expressed as: then the next month is December,” does not assert
that November causes December to occur; rather, the
NA PSC sequence of months suggests that December follows
(Antecedent/determinant Consequent/ November (Dubin, 1978; Giere, 1979).
resultant) Giere (1997) further differentiates deterministic
models from probabilistic models in his discussion of
A sufficient condition asserts that one variable causal statements. Theoretical statements from a de-
results in the occurrence of another variable. It does terministic model assert that the presence or absence
not claim it is the only variable that can result in of one variable determines the presence or absence of
the occurrence of the other variable. This statement a second variable. The probabilistic model is another
asserts that nurse approval of a patient’s self-care approach that views humans as complex social and
behaviors is sufficient for the occurrence of the patient’s environmental phenomena best conceptualized from
self-care activities. However, patient assumption of a probability framework. Probabilistic statements
self-care activities resulting from other factors, such generally are based on statistical data and assert
as the patient’s health status and personality variables, relationships between variables that do not occur in
is not ruled out. There may be other antecedent con- every instance, but are likely to occur based on some
ditions sufficient for the patient’s assumption of self- estimate of probability. As an example, it has been
care activities. asserted that a lack of exercise may lead to obesity, a
A statement in the form of a necessary condition growing national health problem. It is clear that a lack
asserts that one variable is required for the occur- of exercise (LE) does not always lead to obesity, be-
rence of another variable. For example: If patients are cause not all couch potatoes become medically obese
motivated to get well (WM 5 wellness motivation) (MO). However, the probability of developing medi-
then they adhere to their prescribed treatment regi- cal obesity (P MO) may be increased for persons who
men (AR). routinely avoid exercise at least to some degree of
probability. In symbolic notation:
WM AR
IF LE P MO
This means that adherence to a treatment regimen
(AR) never occurs unless wellness motivation (WM) Relational statements that assert connections
occurs. It is not asserted that the patients’ adherence between variables provide for analysis and establish
to the treatment regimen stems from their wellness a basis for explanation and prediction (Hage, 1972).
motivation. However, it is asserted that if the wellness
motivation is absent, patients will not assume strict Linkages and Ordering
adherence to their treatment regimens. The wellness Specification of linkages is a vital part of the develop-
motivation is a necessary, but not a sufficient, condi- ment of theory (Hage, 1972). Although the theoretical
tion for the occurrence of this consequent. statements assert connections between concepts, the
The term if is generally used to introduce a suffi- rationale for the stated connections must be developed
cient condition, whereas only if and if . . . then are and clearly presented. Development of theoretical link-
used to introduce necessary conditions (Giere, 1979). ages provides an explanation of why the variables
Usually conditional statements are not both necessary are connected in a certain manner; that is, the theo-
and sufficient. However, it is possible for a statement retical reason for particular relationships (Hage,
to express both conditions. In such instances, the 1972). Operational linkages contribute testability to
term if and only if is used to imply that conditions are the theory by specifying how measurement variables
both necessary and sufficient for one another. In this are connected (Hage, 1972). Operational definitions