The Theory of Planned Behavior

ORGANIZATIONAL BEHAVIOR AND HUMAN DECISION PROCESSES 50, 179-211 (1991)
The Theory of Planned Behavior
ICEK AJZEN
University of Massachusetts at Amherst
Research dealing with various aspects of* the theory of planned behavior (Ajzen, 1985,
1987) is reviewed, and some unresolved issues are discussed. In broad terms, the theory is
found to be well supported by empirical evidence. Intentions to perform behaviors of different
kinds can be predicted with high accuracy from attitudes toward the behavior, subjective
norms, and perceived behavioral control; and these intentions, together with perceptions of
behavioral control, account for considerable variance in actual behavior. Attitudes, subjective
norms, and perceived behavioral control are shown to be related to appropriate sets of salient
behavioral, normative, and control beliefs about the behavior, but the exact nature of these
relations is still uncertain. Expectancy— value formulations are found to be only partly
successful in dealing with these relations. Optimal rescaling of expectancy and value
measures is offered as a means of dealing with measurement limitations. Finally, inclusion of
past behavior in the prediction equation is shown to provide a means of testing the theory*s
sufficiency, another issue that remains unresolved. The limited available evidence concerning
this question shows that the theory is predicting behavior quite well in comparison to the
ceiling imposed by behavioral reliability. © 1991 Academic Press. Inc.
As every student of psychology knows, explaining human behavior in
all its complexity is a difficult task. It can be approached at many levels,
from concern with physiological processes at one extreme to concentra-
tion on social institutions at the other. Social and personality psycholo-
gists have tended to focus on an intermediate level, the fully functioning
individual whose processing of available information mediates the effects
of biological and environmental factors on behavior. Concepts referring
to behavioral dispositions, such as social attitude and personality trait,
have played an important role in these attempts to predict and explain
human behavior (see Ajzen, 1988; Campbell, 1963; Sherman & Fazio,
1983). Various theoretical frameworks have been proposed to deal with
the psychological processes involved. This special edition of Organiza-
tional Behavior and Human Decision Processes concentrates on cogni-
I am very grateful to Nancy DeCourville, Richard Netemeyer, Michelle van Ryn, and Amiram
Vinokur for providing unpublished data sets for reanalysis, and to Edwin Locke for his comments on
an earlier draft of this article. Address correspondence and reprint requests to Icek Ajzen, Department
of Psychology, University of Massachusetts, Amherst, MA 01003-0034.
0749-5978/91 $3.00
Copyright C 1991 by Academic Press. Inc.
All rights of reproduction in any form reserved.

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ICEK AJZEN
tive self-regulation as an important aspect of human behavior. In the pages
below I deal with cognitive self-regulation in the context of a dispositional
approach to the prediction of behavior. A brief examination of past efforts
at using measures of behavioral dispositions to predict behavior is
followed by presentation of a theoretical model—the theory of planned
behavior—in which cognitive self-regulation plays an important part.
Recent research findings concerning various aspects of the theory are
discussed, with particular emphasis on unresolved issues.
DISPOSITIONAL PREDICTION OF HUMAN BEHAVIOR
Much has been made of the fact that general dispositions tend to be
poor predictors of behavior in specific situations. General attitudes have
been assessed with respect to organizations and institutions (the church,
public housing, student government, one*s job or employer), minority
groups (Blacks, Jews, Catholics), and particular individuals with whom a
person might interact (a Black person, a fellow student). (See Ajzen &
Fishbein, 1977, for a literature review.) The failure of such general atti-
tudes to predict specific behaviors directed at the target of the attitude has
produced calls for abandoning the attitude concept (Wicker, 1969).
In a similar fashion, the low empirical relations between general per-
sonality traits and behavior in specific situations has led theorists to claim
that the trait concept, defined as a broad behavior disposition, is untenable
(Mischel, 1968). Of particular interest for present purposes are attempts to
relate generalized locus of control (Rotter, 1954, 1966) to behaviors in
specific contexts. As with other personality traits, the results have been
disappointing. For example, perceived locus of control, as assessed by
Rotter*s scale, often fails to predict achievement-related behavior (see
Warehime, 1972) or political involvement (see Levenson, 1981) in a
systematic fashion; and somewhat more specialized measures, such as
health-locus of control and achievement-related locus of control, have not
fared much better (see Lefcourt, 1982; Wallston & Wallston, 1981).
One proposed remedy for the poor predictive validity of attitudes and
traits is the aggregation of specific behaviors across occasions, situaions,
and forms of action (Epstein, 1983; Fishbein & Ajzen, 1974). The idea
behind the principle of aggregation is the assumption that any single
ample of behavior reflects not only the influence of a relevant general
disposition but also the influence of various other factors unique to the
particular occasion, situation, and action being observed. By aggregating
different behaviors, observed on different occasions and in different sit-
ations, these other sources of influence tend to cancel each other, with the
result that the aggregate represents a more valid measure of the un-
derlying behavioral disposition than any single behavior. Many studies

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THEORY OF PLANNED BEHAVIOR
181
performed in recent years have demonstrated the workings of the aggre-
gation principle by showing that general attitudes and personality traits do
in fact predict behavioral aggregates much better than they predict specific
behaviors. (See Ajzen, 1988, for a discussion of the aggregation principle
and for a review of empirical research.)
ACCOUNTING FOR ACTIONS IN SPECIFIC CONTEXTS:
THE THEORY OF PLANNED BEHAVIOR
The principle of aggregation, however, does not explain behavioral
variability across situations, nor does it permit prediction of a specific
behavior in a given situation. It was meant to demonstrate that general
attitudes and personality traits are implicated in human behavior, but that
their influence can be discerned only by looking at broad, aggregated,
valid samples of behavior. Their influence on specific actions in specific
situations is greatly attenuated by the presence of other, more immediate
factors. Indeed, it may be argued that broad attitudes and personality traits
have an impact on specific behaviors only indirectly by influencing some
of the factors that are more closely linked to the behavior in question (see
Ajzen & Fishbein, 1980, Chap. 7). The present article deals with the
nature of these behavior-specific factors in the framework of the theory of
planned behavior, a theory designed to predict and explain human
behavior in specific contexts. Because the theory of planned behavior is
described elsewhere (Ajzen, 1988), only brief summaries of its various
aspects are presented here. Relevant empirical findings are considered as
each aspect of the theory is discussed.
Predicting Behavior: Intentions and Perceived Behavioral Control
The theory of planned behavior is an extension of the theory of rea-
soned action (Ajzen & Fishbein, 1980; Fishbein & Ajzen, 1975) made
necessary by the original model*s limitations in dealing with behaviors
over which people have incomplete volitional control. Figure 1 depicts the
theory in the form of a structural diagram. For ease of presentation,
possible feedback effects of behavior on the antecedent variables are not
shown.
As in the original theory of reasoned action, a central factor in the
theory of planned behavior is the individual*s intention to perform a given
behavior. Intentions are assumed to capture the motivational factors that
influence a behavior; they are indications of how hard people are willing
to try, of how much of an effort they are planning to exert, in order to
perform the behavior. As a general rule, the stronger the intention to
engage in a behavior, the more likely should be its performance. It should
be clear, however, that a behavioral intention can find expression in
behavior only if the behavior in question is under volitional control, i.e.,

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FIG. 1. Theory of planned behavior
if the person can decide at will to perform or not perform the behavior.
Although some behaviors may in fact meet this requirement quite well, the
performance of most depends at least to some degree on such non-
motivational factors as availability of requisite opportunities and re-
sources (e.g., time, money, skills, cooperation of others; see Ajzen, 1985,
for a discussion). Collectively, these factors represent people*s actual
control over the behavior. To the extent that a person has the required
opportunities and resources, and intends to perform the behavior, he or
she should succeed in doing so.1
The idea that behavioral achievement depends jointly on motivation
(intention) and ability (behavioral control) is by no means new. It consti-
tutes the basis for theorizing on such diverse issues as animal learning
(Hull, 1943), level of aspiration (Lewin, Dembo, Festinger, & Sears,
1The original derivation of the theory of planned behavior (Aizen, 1985) defined intention (and its
other theoretical constructs) in terms of trying to perform a given behavior rather than in relation to
actual performance. However, early work with the model showed strong correlations between
measures of the model*s variables that asked about trying to perform a given behavior and measures
that dealt with actual performance of the behavior (Schifter & Ajzen, 1985; Ajzen & Madden, 1986).
Since the latter measures are less cumbersome, they have been used in subsequent research, and the
variables are now defined more simply in relation to behavioral performance. See, however, Bagozzi
and Warshaw (1990, in press) for work on the concept of trying to attain a behavioral goal.

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THEORY OF PLANNED BEHAVIOR
183
1944), performance on psychomotor and cognitive tasks (e.g., Pleishman,
1958; Locke, 1965; Vroom, 1964), and person perception and attribution
(e.g., Heider, 1944; Anderson, 1974). It has similarly been suggested that
some conception of behavioral control be included in our more general
models of human behavior, conceptions in the form of “facilitating
Factors” (Triandis, 1977), “the context of opportunity” (Sarver, 1983),
‘resources” (Liska, 1984), or “action control” (KuhI, 1985). The as-
sumption is usually made that motivation and ability interact in their
effects on behavioral achievement. Thus, intentions would be expected to
influence performance to the extent that the person has behavioral control,
and performance should increase with behavioral control to the extent that
the person is motivated to try. Interestingly, despite its intuitive
plausibility, the interaction hypothesis has received only limited empirical
support (see Locke, Mento, & Katcher, 1978). We will return to this issue
below.
Perceived behavioral control. The importance of actual behavioral control
is self evident: The resources and opportunities available to a person must
to some extent dictate the likelihood of behavioral achievement. Of
greater psychological interest than actual control, however, is the per-
ception of behavioral control and is impact on intentions and actions.
Perceived behavioral control plays an important part in the theory of
planned behavior. In fact, the theory of planned behavior differs from the
theory of reasoned action in its addition of perceived behavioral control.
Before considering the place of perceived behavioral control in the
prediction of intentions and actions, it is instructive to compare this con-
struct to other conceptions of control. Importantly, perceived behavioral
control differs greatly from Rotter*s (1966) concept of perceived locus of
control. Consistent with an emphasis on factors that are directly linked to
a particular behavior, perceived behavioral control refers to people*s per-
ception of the ease or difficulty of performing the behavior of interest.
Whereas locus of control is a generalized expectancy that remains stable
across situations and forms of action, perceived behavioral control can,
and usually does, vary across situations and actions. Thus, a person may
believe that, in general, her outcomes are determined by her own behavior
(internal locus of control), yet at the same time she may also believe that
her chances of becoming a commercial airplane pilot are very slim (low
perceived behavioral control).
Another approach to perceived control can be found in Atkinson*s
(1964) theory of achievement motivation. An important factor in this the-
ory is the expectancy of success, defined as the perceived probability of
succeeding at a given task. Clearly, this view is quite similar to perceived
behavioral control in that it refers to a specific behavioral context and not
to a generalized predisposition. Somewhat paradoxically, the motive to

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achieve success is defined not as a motive to succeed at a given task but in
terms of a general disposition “which the individual carries about him
from one situation to another” (Atkinson, 1964, p. 242). This general
achievement motivation was assumed to combine multiplicatively with the
situational expectancy of success as well as with another situation-specific
factor, the “incentive value” of success.
The present view of perceived behavioral control, however, is most
compatible with Bandura*s (1977, 1982) concept of perceived self-
efficacy which “is concerned with judgments of how well one can execute
courses of action required to deal with prospective situations” (Bandura,
1982, p. 122). Much of our knowledge about the role of perceived
behavioral control comes from the systematic research program of
Bandura and his associates (e.g., Bandura, Adams, & Beyer, 1977;
Bandura, Adams, Hardy, & Howells, 1980). These investigations have
shown that people*s behavior is strongly influenced by their confidence in
their ability to perform it (i.e., by perceived behavioral control). Self-
efficacy beliefs can influence choice of activities, preparation for an
activity, effort expended during performance, as well as thought patterns
and emotional reactions (see Bandura, 1982, 1991). The theory of planned
behavior places the construct of self-efficacy belief or perceived
behavioral control within a more general framework of the relations
among beliefs, attitudes, intentions, and behavior.
According to the theory of planned behavior, perceived behavioral con-
trol, together with behavioral intention, can be used directly to predict
behavioral achievement. At least two rationales can be offered for this
hypothesis. First, holding intention constant, the effort expended to bring
a course of behavior to a successful conclusion is likely to increase with
perceived behavioral control. For instance, even if two individuals have
equally strong intentions to learn to ski, and both try to do so, the person
who is confident that he can master this activity is more likely to perse-
vere than is the person who doubts his ability.2 The second reason for
expecting a direct link between perceived behavioral control and behav-
ioral achievement is that perceived behavioral control can often be used as
a substitute for a measure of actual control. Whether a measure of
perceived behavioral control can substitute for a measure of actual control
depends, of course, on the accuracy of the perceptions. Perceived
behavioral control may not be particularly realistic when a person has
2 It may appear that the individual with high perceived behavioral control should also have
a stronger intention to learn skiing than the individual with low perceived control.
However, as we shall see below, intentions are influenced by additional factors, and it is
because of these other factors that two individuals with different perceptions of behavioral
control can have equally strong intentions.

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THEORY OF PLANNED BEHAVIOR
185
relatively little information about the behavior, when requirements or
available resources have changed, or when new and unfamiliar elements
have entered into the situation. Under those conditions, a measure of
perceived behavioral control may add little to accuracy of behavioral
prediction. However, to the extent that perceived control is realistic, it can
be used to predict the probability of a successful behavioral attempt
(Ajzen, 1985).
Predicting Behavior: Empirical Findings
According to the theory of planned behavior, performance of a behavior
is a joint function of intentions and perceived behavioral control. For
accurate prediction, several conditions have to be met. First, the measures
of intention and of perceived behavioral control must correspond to (Ajzen
& Fishbein, 1977) or be compatible with (Ajzen, 1988) the behavior that
is to be predicted. That is, intentions and perceptions of control must be
assessed in relation to the particular behavior of interest, and the specified
context must be the same as that in which the behavior is to occur. For
example, if the behavior to be predicted is “donating money to the Red
Cross,” then we must assess intentions “to donate money to the Red
Cross” (not intentions “to donate money” in general nor intentions “to
help the Red Cross”), as well as perceived control over “donating money
to the Red Cross.” The second condition for accurate behavioral
prediction is that intentions and perceived behavioral control must remain
stable in the interval between their assessment and observation of the
behavior. Intervening events may produce changes in intentions or in
perceptions of behavioral control, with the effect that the original mea-
sures of these variables no longer permit accurate prediction of behavior.
The third requirement for predictive validity has to do with the accuracy
of perceived behavioral control. As noted earlier, prediction of behavior
from perceived behavioral control should improve to the extent that per-
ceptions of behavioral control realistically reflect actual control.
The relative importance of intentions and perceived behavioral control
in the prediction of behavior is expected to vary across situations and
across different behaviors. When the behavior/situation affords a person
complete control over behavioral performance, intentions alone should be
sufficient to predict behavior, as specified in the theory of reasoned ac-
tion. The addition of perceived behavioral control should become increas-
ingly useful as volitional control over the behavior declines. Both, inten-
tions and perceptions of behavioral control, can make significant contri-
butions to the prediction of behavior, but in any given application, one
may be more important than the other and, in fact, only one of the two
predictors may be needed.
Intentions and behavior. Evidence concerning the relation between

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ICEK AJZEN
intentions and actions has been collected with respect to many different
types of behaviors, with much of the work done in the framework of the
theory of reasoned action. Reviews of this research can be found in a
variety of sources (e.g., Ajzen, 1988; Ajzen & Fishbein, 1980; Canary &
Seibold, 1984; Sheppard, Hartwick, & Warshaw, 1988). The behaviors
involved have ranged from very simple strategy choices in laboratory
games to actions of appreciable personal or social significance, such as
having an abortion, smoking marijuana, and choosing among candidates in
an election. As a general rule it is found that when behaviors pose no
serious problems of control, they can be predicted from intentions with
considerable accuracy (see Ajzen, 1988; Sheppard, Hartwick, & Warshaw,
1988). Good examples can be found in behaviors that involve a choice
among available alternatives. For example, people*s voting intentions,
assessed a short time prior to a presidential election, tend to correlate with
actual voting choice in the range of .75 to .80 (see Fishbein & Ajzen,
1981). A different decision is at issue in a mother*s choice of feeding
method (breast versus bottle) for her newborn baby. This choice was
found to have a correlation of .82 with intentions expressed several weeks
prior to delivery (Manstead, Proffitt, & Smart, 1983).
Perceived behavioral control and behavior. In this article, however, we
focus on situations in which it may be necessary to go beyond totally
controllable aspects of human behavior. We thus turn to research con-
ducted in the framework of the theory of planned behavior, research that
has tried to predict behavior by combining intentions and perceived be-
havioral control. Table 1 summarizes the results of several recent studies
that have dealt with a great variety of activities, from playing video games
and losing weight to cheating, shoplifting, and lying.
Looking at the first four columns of data, it can be seen that both
predictors, intentions and perceived behavioral control, correlate quite
well with behavioral performance. The regression coefficients show that
in the first five studies, each of the two antecedent variables made a
significant contribution to the prediction of behavior. In most of the re-
maining studies, intentions proved the more important of the two predic-
tors; only in the case of weight loss (Netemeyer, Burton, & Johnston,
1990; Schifter & Ajzen, 1985) did perceived behavioral control over-
shadow the contribution of intention.
The overall predictive validity of the theory of planned behavior is
shown by the multiple correlations in the last column of Table 1. It can be
seen that the combination of intentions and perceived behavioral control
3Intention–behavior correlations are, of course, not always as high as this. Lower cor-
relations can be the result of unreliable or invalid measures (see Sheppard. Hartwick, &
Warshaw, 1988) or, as we shall see below, due to problems of volitional control.

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TABLE 1
PREDICTION OF BEHAVIOR (B) FROM INTENTION (I) AND PERCEIVED
BEHAVIORAL CONTROL (PBC)
Regression
Correlations
coefficients
Study
Activity
I
PBC
I
PBC
R
van Ryn & Vinokur (1990)
Job search, 10-activity index
1-month behavior post-testa
.41
.20
.38 .13
.42
Doll & Ajzen (1990)
Playing six video games
Mean within-subjects
.49
.48
.14
.12
.51
Schlegel et al. (1990)
Problem drinking — frequency
.47
.48
.28
.32
.53
— quantity
.41
.60
.29
.43
.64
Ajzen & Driver (in press, a)
Five leisure activities
Mean within-subjects
.75
.73
.46
.37
.78
Locke et al. (1984)b
Performance on cognitive taska
.57
.61
.34
.42
.66
Watters (1989)
Election participation
.45
.31
.39
.19
.49
Voting choice
.84
.76
.80
.05*
.84
Netemeyer, Burton, & Johnston
Election participationa
.41
.15
.52
.18*
.43
(1990)
Losing weighta
.18
.22
.08*
.18
.23
Schifter & Ajzen (1985)
Madden, Ellen, & Ajzen (in
Losing weight
.25
.41
.09*
.39
.44
press)
10 common activities
Ajzen & Madden (1986)
Mean within-subjects
.38
.28
.34
.17
.42
Attending class
.36
.28
.30
.11*
.37
Getting an ‘A* in a course
Beginning of semester
.26
.11*
.26
– .01*
.26
End of semester
.39
.38
.27
.26
.45
Beck & Ajzen (in press)
CCheating, shoplifting, lying—mean
.52
.44

.46 .08*
.53
Netemeyer. Andrews, &
GGiving a gift — mean
Durvasula (1990)
over five items
.52
.24
.52 .02*
.53
* Not significant; all other coefficients significant at p < .05.
a Not a direct test of the theory of planned behavior.
b Secondary analysis.
permitted significant prediction of behavior in each case, and that many of
the multiple correlations were of substantial magnitude. The multiple cor-
relations ranged from .20 to .78, with an average of .51. Interestingly, the
weakest predictions were found with respect to losing weight and getting
an ‘A* in a course. Of all the behaviors considered, these two would seem
to be the most problematic in terms of volitional control, and in terms of
the correspondence between perceived and actual control. Some confir-
mation of this speculation can be found in the study on academic perfor-
mance (Ajzen & Madden, 1986) in which the predictive validity of per-
ceived behavioral control improved from the beginning to the end of the
semester, presumably because perceptions of ability to get an ‘A* in the
course became more realistic.
Another interesting pattern of results occurred with respect to political
behavior. Voting choice in the 1988 presidential election (among respon-
dents who participated in the election) was highly consistent ( r = .84 )
with previously expressed intentions (Watters, 1989). Voting choice, of
course, poses no problems in terms of volitional control, and perceptions

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ICEK AJZEN
of behavioral control were found to be largely irrelevant. In contrast,
participating in an election can be subject to problems of control even if
only registered voters are considered: lack of transportation, being ill, and
other unforeseen events can make participation in an election relatively
difficult. In Watters*s (1989) study of the 1988 presidential election, per-
ceived behavioral control indeed had a significant regression coefficient,
although this was not found to be the case in a study of participation in a
gubernatorial election primary (Netemeyer et a!., 1990).
Intention x control interaction. We noted earlier that past theory as well
as intuition would lead us to expect an interaction between motivation and
control. In the context of the theory of planned behavior, this expectation
implies that intentions and perceptions of behavioral control should
interact in the prediction of behavior. Seven of the studies shown in Table
I included tests of this hypothesis (Doll & Ajzen, 1990; Ajzen & Driver,
in press, a; Watters, 1989; Schifter & Ajzen, 1985; Ajzen & Madden,
1986; Beck & Ajzen, 1990). Of these studies, only one (Schifter & Ajzen,
1985) obtained a marginally significant (p < .10) linear x linear interaction
between intentions to lose weight and perceptions of control over this
behavioral goal. In the remaining six studies there was no evidence for an
interaction of this kind. It is not clear why significant interactions failed to
emerge in these studies, but it is worth noting that linear models are
generally found to account quite well for psychological data, even when
the data set is known to have been generated by a multiplicative model
(Birnbaum, 1972; Busemeyer & Jones, 1983).
Predicting Intentions: Attitudes, Subjective Norms, and Perceived
Behavioral Control
The theory of planned behavior postulates three conceptually indepen-
dent determinants of intention. The first is the attitude toward the behav-
ior and refers to the degree to which a person has a favorable or unfa-
vorable evaluation or appraisal of the behavior in question. The second
predictor is a social factor termed subjective norm; it refers to the per-
ceived social pressure to perform or not to perform the behavior. The third
antecedent of intention is the degree of perceived behavioral control
which, as we saw earlier, refers to the perceived ease or difficulty of
performing the behavior and it is assumed to reflect past experience as
well as anticipated impediments and obstacles. As a general rule, the
more favorable the attitude and subjective norm with respect to a behav-
ior, and the greater the perceived behavioral control, the stronger should
be an individual*s intention to perform the behavior under consideration.
The relative importance of attitude, subjective norm, and perceived be-
havioral control in the prediction of intention is expected to vary across
behaviors and situations. Thus, in some applications it may be found that

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