  (Abridged) A new method is presented to identify transient candidates in
large-scale surveys based on the variability pattern in their light curves. The
method is based on the Abbe value, that estimates the smoothness of a light
curve, and on a newly introduced value called the excess Abbe that estimates
the regularity of the light curve variability pattern over the duration of the
observations. Based on simulated light curves, transients are shown to occupy a
specific region in the Abbe versus Excess Abbe diagram, distinct from sources
presenting pulsating-like features in their light curves or having featureless
light curves.
  The method is tested on real light curves taken from EROS-2 and OGLE-II
surveys in a 0.50deg x 0.17deg field of the sky in the LMC. The method
identifies 43 EROS-2 transient candidates out of a total of ~1300 variable
stars, and 19 more OGLE-II candidates. The efficiency of the method is further
tested by comparing the list of transient candidates with known Be stars in the
literature. It is shown that all Be stars known in the studied field of view
with detectable bursts or outbursts are successfully extracted by the method.
In addition, four new transient candidates displaying bursts and/or outbursts
are found in the field, of which at least two are good new Be candidates.
  The new method proves to be a potentially powerful tool to extract transient
candidates from large-scale multi-epoch surveys. The better the photometric
measurement uncertainties are, the cleaner the list of detected transient
candidates is. In addition, the diagram is shown to be a good diagnostic tool
to check the data quality of multi-epoch photometric surveys. A trend of
instrumental and/or data reduction origin, for example, will manifest itself by
an unexpected distribution of points in the diagram.
