the intervention, both groups recei

the intervention, both groups received questionnaires by mail.
Reminder calls encouraged participants to fill out and return the
questionnaire.
Measures
A questionnaire was developed and modified based on a comprehensive
literature review. 3,8,9 Measures used included demographic
information, self-reported assessments of readiness for passive
smoking avoidance (stages of change), TTM psychological
constructs associated with passive smoking avoidance (decisional
balance pros and cons, self-efficacy and use of experiential and
behavioural strategies for behavioural change) and questions about
knowledge of adverse health effects of passive smoking. The questionnaire
was reviewed for content validity by seven health professionals.
The content validity index was 0.89.
Stages of change
Participants selected one of five statements best representing their
current intentions of taking preventive behaviours against passive
smoking. Discrete stages (precontemplation, contemplation/preparation
or action/maintenance) were determined by an algorithm
based on response options.
Decisional balance
Decisional balance pros and cons were measured using an 8-item
inventory assessing perceived benefits and barriers to avoid passive
smoking. Participants rated statements on a 5-point Likert-type
scale as to the level of influence each statement had on their
decision to engage in preventive behaviour or deciding to take
action on avoiding passive smoking. The scale ranged from
1 = ‘little influence’ to 5 = ‘great influence’. Internal consistency
was pros = .73 and cons = .90.
Processes of change
Experiential and behavioural processes of change were assessed by
20 items regarding frequency of avoiding passive smoking.
Participants indicated frequency of use for each process within the
past month on a 5-point Likert-type scale ranging from 1 = ‘never’
to 5 = ‘always’. Internal consistency coefficients for process scales
were .80 to .87.
Self-efficacy
Self-efficacy in avoiding passive smoking was measured using
a 4-item instrument. Participants endorsed each item using a
5-point Likert scale ranging from 1 ‘no confidence at all’ to
5 ‘complete confidence’. Internal consistency coefficients for the
process scales were .68.
Knowledge
Knowledge related to adverse health effects of passive smoking
was measured with 16 yes/no items. Internal consistency of the
knowledge scale assessed by Kuder–Richardson 20 was 0.62.
Power consideration
Average effect size for t-test situations was .35 based on previous
analysis of nursing publications.15 Assumed effect size of 0.35 was
used to estimate sample size needs. Using a general power analysis
programme (G*Power 2 software) with a power of .80 and alpha
of .05, sample size requirement was 260, allowing group differences
to be detected by t-test in our sample of 292 women.
Data analysis
All data were analysed using the Statistical Product and Service
Solution (SPSS) 15.0 (SPSS Inc., Chicago, IL, USA). Background
variables were described by percentages, means and standard
deviations. Student t-test and chi-squared test were used to
evaluate differences in background characteristics and in baseline
TTM measures between the intervention and comparison groups
and between mothers with children and pregnant women within
the two groups. Differences between the two groups in indicators
of programme effectiveness were examined with either analysis of
covariance (ANCOVA) or McNemar test. ANCOVA used pre-test
scores as a covariate, and mean ages of participants were treated as
controlling variables owing to significant differences between the
two groups. Model included intervention status, pre-test scores
and any baseline variables for which conditions differed.
Results
Characteristics of study subjects
Background characteristics of study subjects are summarized in
table 1. The mean ages of pregnant women in the intervention
group were significantly higher than those of pregnant women in
the comparison group (31.29 years vs. 29.45 years, respectively;
P = 0.021).
Determinants of change: knowledge
No significant differences were found between the two groups and
both types of participants in mean knowledge scores at pre-test
(table 2). There were no significant differences in the post-test
scores between mothers and pregnant women within both intervention
and comparison groups after adjusting for pre-test scores and age
(table 3). ANCOVA results showed that the differences between the
intervention group and comparison group were statistically significant
(P < .001) for both mother with child and pregnant women.
Determinants of change: processes of change
No significant differences were found between the two groups or
between both types of participants in experiential and behavioural
processes scores at baseline (table 2). There were significant differences
in the post-test scores of experiential processes between mothers
and pregnant women in the comparison group after adjusting for
pre-test scores and age (F

ผลลัพธ์ (ไทย) 3:

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