Table 1.

Newcastle–Ottawa Scale

Study	Selection				Comparability		Exposure			Number of stars
	S1	S2	S3	S4	C1	C2	E1	E2	E3
Memeo et al.	X	X	X		X	X	X		X	7
Shelbourne et al.	X	X	X	X	X	X	X	X	X	9
Fuchs et al.	X	X	X	X	X	X	X	X	X	9
McCarrol et al.	X	X	X		X	X	X	X	X	8