  When a microlensing light curve is contaminated by blended light from
unresolved stars near the line of sight to the lensed star, the light curve
shape and corresponding parameterization for the event will differ from the
values expected when the event is not affected by blending. As a result,
blending makes it difficult to identify the major lens population and to
estimate the amount of lensing matter. In order to estimate the effect of
blending on the result of lensing experiments, it is, therefore, essential to
know how the observed lensing parameters change depending on the fraction of
blended light. Previously, the changed lensing parameters were obtained with a
statistical method that not only required a large amount of computation time
but also was prone to uncertainty. In this paper, we derive analytic relations
between the lensing parameters with and without the effect of blending. By
using these relations, we investigate the dependence of the observed lensing
parameters on the amount of blended light, the impact parameter, and the
threshold amplification for event detection.
