Statistical analysis
The obtained data were analyzed using SPSS Statistics version 22. All
blood pressure values are presented as mean±SD. First, using a paired
t-test, the SBP and DBP measured with the CDXP and the Omron M6 Comfort
were compared to the aneroid manometer. Second, a linear regression
analysis was used to determine whether body mass index, parity,
gestational age, upper arm circumference and wrist circumference had any
influence on the blood pressure differences between the devices. Third,
Bland-Altman plots were created to visualize the performance of the
devices. Following the ESH-IP 2010 protocol, the found blood pressure
differences were divided into four groups: difference of ≤5 mmHg, ≤10
mmHg, ≤15 mmHg and >15 mmHg. Fourth, the systolic and
diastolic blood pressure of the office measurements and the home
self-measurements of the CDXP were compared by using a paired t-test.
When applicable, Bonferroni correction was applied for multiple
comparisons. The SUS score was calculated with the first ten questions
of the questionnaire following the standard ranging from 0 till
100%22. The mean score from the other 5 questions was
calculated, ranging from 1 till 5.
To achieve a power of 95% with an α significance level of 0.05 a sample
size of 22 was estimated, with the variation of difference in blood
pressure being 5 mmHg and the chosen relevant difference being 5 mmHg.
All analyses were carried out using SPSS version 22. P-values less than
0.05 were considered statistically significant.