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.