Educability-and-Group-Differences-1973-by-Arthur-Robert-Jensen

Culture-biased Tests 309
easy items to the last, most difficult items.4 The PPVT pictures
and labels are almost a parody of culture-biased tests: e.g.,
kangaroo, caboose, thermos, bronco, kayak, hassock, goblet, binocular,
idol, observatory, oasis, walrus, canine.
The Raven and PPVT were given individually to all white
(N = 638), Negro (N = 381), and Mexican-American (N = 684)
elementary school children in one small California school district.5
The raw scores on both tests, within 6-month age intervals, were
PPVT Items
Figure 17.4 Mean Thorndike-Lorge word frequency of Peabody
Picture Vocabulary Test items (for Forms A and B) as a function
of item difficulty when items are ranked from 1 to 150 in P values
(percent passing), based on the normative population.
transformed to z scores, with mean = 0, SD = 1. The regression
of Raven on PPVT and of PPVT on Raven was then plotted
separately for each ethnic group. The regression lines are perfectly
linear throughout the entire range of test scores in all three groups,
as showrn in Figure 17.5. The slopes of these regression lines of
the three groups do not differ significantly, but the intercepts
differ significantly beyond the 0-001 level (F = 52-38, df = 2/1658).
In short, the differences essential to our hypotheses are fully
significant. So let us compare these empirical regression lines
with the hypothesized ones in Figure 17.3. First consider the