Table 2.

Internal validity scores (b1, b2, c, e, f, g, j, l, n)

reference	b1	b2	c	e	f	g	j	l	n
Vassilomaniakis 1995	+	‐	+	+	‐	‐	+	+	+
Ranson 1990	+	+	+	+	+	+?	+	+	+?
Lim 1993	+	‐	+	+	‐	+?	+	+	+
Barriga 1997	+	+	+	+	+	+	+	+	+
Rackoff 1995	+	+	+	+	+	+	+	+	+
Schwartz 1990	+	+	+	+	+	+	+	+	+
Henrickson 2000	+	+	+	+	+	+	+	+	+
Daghistani 1996	+	+	+	+	+	+?	+	+	+
Ljungman 1997	+	‐	‐	‐	‐	‐	+	+	+
Di Carlo 2011	+	+	+	+	‐	‐	+	+	?
Handrup 2013	+	‐	+	+	‐	‐	+	+	+