Table 1.

Studies showing higher concentration of iron in PD substantia nigra compared to control

Author (year)	Method	No of PD samples	No of control samples	PD/control ratio
Earle (1968)	XFS	11	?	2 ± ?
Sofic et al. (1988)	SPH	8	8	1.77 ± 0.37
Griffiths and Crossman (1993)	AA	6	6	2.01 ± 0.24
Mann et al. (1994)	ICP	18	22	1.56 ± 0.69
Dexter et al. (1989)	ICP	7	9	1.34 ± 0.17

PD/control was calculated with the standard error of the ratio

XFS X-ray fluorescent spectroscopy, SPH spectrophotometry, AA atomic absorption, ICP inductively coupled plasma spectroscopy