Measuring Electron Efficiencies at CMS with Early Data

In this note we describe the ``tag and probe" methods that have been developed to measure both online and offline electron efficiencies from data at CMS. We present their implementation in the CMS software framework (CMSSW) and their validation with both Monte Carlo truth and reconstructed physics observables. We also discuss methods for background estimation and subsequent correction of efficiencies due to this background contamination. We suggest an electron efficiency factorization scheme and apply it using the ``tag and probe" tools in support of the measurement of $\sigma \times BR(pp \rightarrow \gammaZee)$ being performed as a preparatory analysis in CMS in anticipation of the start of LHC operation in 2008.