previous picks the samples before the current one. For example, given the following case fragment:
01 Jun 03 20 Jun 03 08 Oct 03 15 Oct 03 02 Nov 03 ABC 2.0 2.1 2.2 2.5 1.9 DEF 6.2* 5.0* 3.5 3.9 GHI 1.0-5.0 6.0* 5.2* 2.3 1.9 5.5*
all previous ABC >= 2.0
no previous ABC < 2.0
all previous previous DEF are not normal (note that ‘previous previous’ trims off the last 2 samples)
some previous DEF is not normal
no previous ( GHI within last 4 weeks ) is high