Sample size calculation
CORONAVIRUS, MAY
A sample size of 172 patients for each strategy was estimated, assuming a 15% increase in effectiveness (from 28% to 43%) of the phone call strategy over the mail strategy (power 80%, alpha error 5%) and a 10% lose in each intervention.For extraordinary reasons that may have influenced the results because of the nature of the study, an unplanned interim analysis was conducted on March 15th, 2020, 5 days before the national lockdown because of the coronavirus pandemic, which included 270 patients (78% of the planned sample size). One strategy was considered to have a statistically significant difference (The switch strategy was postponed after the lockdown was finished and normality arrived at hospital appointments (May 2021).