Bonilha and colleagues (2008) measured brain volume reduction in a region of the prefrontal cortex called Brodmann Area 9 (BA9) in a sample of 14 adult patients with schizophrenia. Participants completed a cognitive performance test called the Wisconsin Card Sorting Test (WCST). The relationship between brain volume reduction and the number of errors on the WCST was measured. The following scatter plot shows the approximate standardized values the researchers measured.
(a) Is the slope positive or negative?
(b) Describe the relationship between prefrontal brain volume in BA9 and cognitive performance on the WCST.