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October 2003

Development of Generalized Myasthenia Gravis in Patients With Ocular Myasthenia Gravis—Reply

Arch Neurol. 2003;60(10):1492-1493. doi:10.1001/archneur.60.10.1491-a

In reply

We thank Dr Wang for his thoughtful analysis of our work and apologize for our mislabeling the Kaplan-Meier curve. The scale is appropriate to the question asked concerning the development of generalized myasthenia gravis.

There are at least 2 reasons why it may not be valid to look at survival in time intervals across a 6-year period. The economist John Maynard Keynes is said to have remarked, "[I]n the long run we are all dead."1 Correspondingly, given enough time, all survival curves tend to converge. Therefore, it may not be useful to look at the entire follow-up period in the presence of long-term survivors. Instead, it may be preferable to look at clinically meaningful spans of time (eg, 5 or 10 years). This will then determine the maximum span of follow-up and the time point when cases should be right censored. This was the approach used in the analysis of the myasthenia gravis data.

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