DAYLITE SAVINGS TIME SERIAL
DAYLITE SAVINGS TIME SERIES

Plots of the partial autocorrelation for lags between 1 and 100 days were utilised in this analysis. The partial autocorrelation function at lag h is an estimate of the correlation between outcome values at all possible time points t and t−h conditional on the observations between time points.

DAYLITE SAVINGS TIME SERIAL

Residuals from the trend/seasonality model were evaluated for residual serial correlation through examination of partial autocorrelation plots and through the Durbin-Watson test statistic, with the p value for the test obtained through bootstrap resampling. The model also adjusted for the additional hour on the day of each fall time change, as well as the loss of an hour on the day of spring time changes through the inclusion of an offset term. 6, 7 This model allowed for a cubic trend in numeric date as well as seasonal factors reflecting weekday (Monday–Friday), monthly (January–December) and yearly (2010–2013) effects.

DAYLITE SAVINGS TIME SERIES

A negative binomial regression model was fitted using the R function glm.nb in the package MASS to assess the existence of and account for trend and seasonal variation in the time series of daily AMI counts. The number of patients with AMI undergoing PCI per day was calculated for each day during the study period. The timing of AMI was the time patients presented to the hospital’s emergency room. 5 Cases not resulting in PCI are not tracked and therefore excluded in this analysis. AMI was defined by a clinical presentation consistent with or suggestive of ischaemia, suggestive or diagnostic ECG changes and cardiac biomarkers (creatine kinase-myocardial band, troponin T or I) exceeding the upper limit of normal according to the individual hospital’s laboratory parameters (typically above the 99th centile of the upper reference limit for normal participants). Procedural data for hospital admissions where PCI was performed in the setting of AMI between 1 January 2010 and 15 September 2013 were included in this analysis. Further details of the data collection are described in previous publications.

To ensure data accuracy, the registry undergoes a rigorous review process including a random audit of 2% of all cases, in addition to a routine review of the medical records of all patients undergoing multiple procedures or coronary artery bypass grafting (CABG) and of patients who die during their hospitalisation. All data elements have been prospectively defined, and the protocol has been either approved or the need for approval waived by local institutional review boards at each of the participating hospitals. A standardised data collection tool is used to gather baseline clinical, demographic, procedural, angiographic and medication data, as well as procedural and in-hospital outcomes for input into the database. In use since 1998, this registry now encompasses all non-federal hospitals in the state of Michigan and has been approved by the institutional review boards of all participating hospitals. The Blue Cross Blue Shield of Michigan Cardiovascular Consortium Percutaneous Coronary Intervention Quality Improvement Initiative (BMC2-PCI) is a prospective, multicentre registry that represents a regional physician-led collaborative effort to assess and improve quality of care and outcomes of all patients with coronary disease who undergo PCI in the state of Michigan.

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