Author Correction: Validation of the Sleep Regularity Index in Older Adults and Associations with Cardiometabolic Risk

Correction to: Scientific Reports 10.1038/s41598-018-32402-5, published online 21 September 2018

The Article contains an error in Equation 3.

$$\frac{1440}{2\pi }\arctan 2\left(\sum _{j=1}^M\sum _{i=1}^M{s}_{i,j}\sin \frac{2\pi t_i}{1440}+\sum _{j=1}^M\sum _{i=1}^M{s}_{i,j}\cos \frac{2\pi t_i}{1440}\right)$$

should read:

$$\frac{1440}{2\pi }\arctan 2\left(\sum _{j=1}^M\sum _{i=1}^M{s}_{i,j}\sin \frac{2\pi t_i}{1440},\sum _{j=1}^M\sum _{i=1}^M{s}_{i,j}\cos \frac{2\pi t_i}{1440}\right)$$

Additionally, the Article contains a typographical error in the Methods section under subheading ‘Calculation of Sleep Regularity Index (SRI) and other sleep indices’ where,

“Sleep midpoint, our index of sleep timing, was calculated as a mean of circular quantities (appropriate for time of day) using the following equation (3), where $t_j$ denotes time of day in minutes at epoch $\mathit{j}$:”

should read:

“Sleep midpoint, our index of sleep timing, was calculated as a mean of circular quantities (appropriate for time of day) using the following equation (3), where $t_j$ denotes time of day in minutes at epoch $j$, and $\arctan 2(x,\mathit{y})$ denotes the angle between $(x,\mathit{y})$ and the positive $x$-axis.”