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For pairs of homologous proteins, secondary structure agreement can be as low as 
[Flores et al., 1993][Russell \& Barton, 1993b].
Figure 7 shows how three-state secondary structure identity (calculated in the same manner as
) behaves as a function of . For type 
similarities, secondary structure agreement is
between 
and 
. For type 
and 
similarities, the possible variation in
secondary structure content is much greater (range of 
), with the lowest observed
pairs having secondary structure identities similar to those for dissimilar structures (between
and 
). Nearly all pairs having secondary structure identities less than 
are
all 
proteins, which could be explained by the shorter (on average) length of strands
compared to 
helices making matches of secondary structure strings longer on average for helix
containing proteins.