Correction: A Twin Protection Effect? Explaining Twin Survival Advantages with a Two-Process Mortality Model

In the Methods section, the third equation in the section titled "Estimating Model Parameters" is incorrect. Please view the complete, correct equation here:

$$l_x^e=\exp \left(-\frac{\lambda \beta }{r}\exp \left(-1/\beta \right)\left(\exp \left(rx/\beta \right)-1\right)\right)$$