Varience differnce in Full Ring vs SH, NL vs Limit

[Piz0wn0reD!!!!!!]

i dont have huge sample sizes, but this is interesting:

A friends stats:

37k hands at full ring 5/10 = SD of 14.3BB/100

88k hands at SH 5/10 = SD of 15.5BB/100

my stats at NL:

84k hands at 100NL Full Ring (2$ Bblind) = SD of 33.4BB/100 (133$/100)

17k hands at 100NL SH (2$ Bblind) = SD of 25.4BB/100 (102$/100)


How can this be? Are my sample sizes too small? Does WR play a large roll in this?

You math guys please tell me what is going on here.