2.2. The TPB questionnaire
The TPB is a theoretical framework but also comprises a set of
guidelines to ensure proper measurement of the social-psychological
constructs. A crucial step in applying the TPB is to define the
behaviour in terms of its target, the action itself, the context in
which it is performed, and when it is performed (the TACT principle).
Then, to conduct a pilot study in which readily accessible behavioural
outcomes, normative referents and control factors regarding the
behaviour are elicited (Francis et al., 2004 & Sok et al., 2021). Our
pilot study included semi-qualitative interviews with 20 dairy farmers
during October-November 2018 (of them, seven dairy farmers were asked
about vaccination against LSD). This gave us a set of underlying beliefs
for each of the constructs (A, SN and PBC). The interviews, as well as
the questionnaire construction, were based on previous studies (Francis
et al., 2004; Sok et al., 2015 & Sok et al., 2016).
The questionnaire included three parts:
1. Questions measuring background factors. These factors were classified
into farm and behavioural variables. The farm variables included
questions on the type of the herd (family farm vs. single/double/triple
cooperative farms), the herd’s yearly milk quota and the location of the
herd. The behavioural variables included questions measuring perceived
past experience and perceived risk as well as general questions
regarding the gender, education and age of the farmer. Perceived risk
was measured by the relative risk attitude and the risk perception. Risk
perception was measured by multiplying two 7-point Likert-type scales,
one with frequencies from ‘once in 100 years’ to ‘once in a week’ and
one with the adjectives ‘No impact’ up to ‘High impact’. For measuring
the relative risk attitude (with respect to animal diseases in general),
each farmer was asked to compare his/her general risk perception to
other farmers. This was performed by filling a 5-point Likert type scale
that ranged from ‘absolutely disagree’ to ‘absolutely agree’, regarding
four statements (Meuwissen et al.,
2001). The TPB framework suggests that the background factors could
explain variation in the intention. However, we examined whether these
factors also have a direct effect on the intention.
2. Questions to obtain
direct measures of the constructs
of the TPB. A 5-points semantic differential scale with four different
bipolar adjective pairs (e.g., unsatisfying and satisfying) was used to
obtain direct measures of attitude. Injunctive subjective norm and PBC
were measured with 5-point bipolar Likert-type scales with the endpoints
”disagree” to ”agree” (Sok et al., 2016). To prevent misinterpretation
of questions regarding negative beliefs, two adjective pairs and one PBC
statement were recoded so that higher numbers always reflect a positive
attitude/self-efficacy/controllability to the target behaviour.
Behavioural intention was measured by asking the farmer to scale his/her
intention to vaccinate against LSD in the coming year between 1 (Will
certainly not vaccinate) to 5 (Will certainly vaccinate). The survey
only queried for measures of the injunctive norm.
Given the distinction between reflective and formative measurement,
direct measures are required to show high internal consistency (see also
Fishbein & Ajzen, 2010 & Sok et al., 2021). We tested the internal
consistency of the direct indicator for each construct by using the
Cronbach’s alpha scores. This analysis revealed a low internal
consistency in the direct measures of the SN and PBC constructs (α=0.6,
0.2 respectively) (Table S1 ). The indicator Nd3, which was
based on the question ”I feel I have social pressure to vaccinate my
herd against LSD in the coming year”, had low within-construct
correlations with the other two indicators (<0.3) and was not
correlated with the intention indicators (Table S1 ). This can
be explained by the disagreement of the farmers with the firmer wording
of this statement as compared to the other two statements. Regarding the
PBC, all three indicators were not correlated with each other. However,
as opposed to indicators Pd1 and Pd2, the indicator Pd3, which was
representing the capacity dimension, did correlate with the intention
(Table S1 ). In addition, although the internal consistency was
appropriate for attitude (∝C value of 0.8), only the indicators Ad1 and
Ad2, which reflected experiential considerations (’necessary’,
’contribute’), had high within-construct correlations and were
correlated with intention (Table S1 ). Overall, to solve for the
low internal inconsistency, we assessed only the indicators which were
correlated with the intention (Ad1 and Ad2 for attitude, Nd1 and Nd2 for
norms, Pd3 for PBC). We calculated the mean of these indicators scores
to give an overall score for each construct.
3. Questions to obtain indirect (belief-based) measures of the three
social-psychological constructs (A, SN, PBC). The most frequently
mentioned responses from the qualitative part of the study were used to
formulate behavioural, normative, and control belief items. Consistent
with the expectancy-value model, for each item the belief strength is
measured at a scale of 5-point Likert type that ranged from ”not very
likely” to ”very likely” for attitude’s beliefs, from ”very against” to
”very in favour for subjective norms’ beliefs and from ”not true” to
”very true” for PBC’s beliefs. Since the subjective norms’ statements
had negative/positive meanings we used a bipolar scaling while we used a
unipolar scaler for the attitude’s and PBC’s statements. The outcome
evaluation/motivation to comply with pressure from the reference
group/power of the control were measured at a scale of 5-point Likert
type that ranged from ”very unimportant” to ”very important”/”not
important” to ”very important”/”more difficult” to ”more easy”. This
time, the power of the control received a bipolar scaling and the
motivation to comply a unipolar scaling. In the analysis we changed the
outcome evaluation scaling from bipolar to unipolar which was more
logically fit (see Fishbein & Ajzen, 2010 & Sok et al., 2021). Certain
behavioural and control belief statements with expected negative
influence on vaccination were recoded as been described for the direct
measurement. The resulting multiplicative products were analysed both
individually and as an average.
The full questionnaire is attached to the supplementary
materials .