Explaining Group Differences

Among researchers, the issue of cultural bias stems largely from well-documented findings, now seen in more than 100 years of research, that members of different ethnic groups have different levels and patterns of performance on many prominent cognitive ability tests. Intelligence batteries have generated some of the most influential and provocative of these findings (Elliot, 1987; Gutkin & Reynolds, 1981; Reynolds, Chastain, Kaufman, & McLean, 1987; Spitz, 1986). In many countries worldwide, people of different ethnic and racial groups, genders, socioeconomic levels, and other demographic groups obtain systematically different intellectual test results. Black-White IQ differences in the United States have undergone extensive investigation for more than 50 years. Jensen (1980), Shuey (1966), Tyler (1965), and Willerman (1979) have reviewed the greater part of this research. The findings occasionally differ somewhat from one age group to another, but they have not changed substantially in the past century.

On average, Blacks differ from Whites by about 1.0 standard deviation, with White groups obtaining the higher scores. The differences have been relatively consistent in size for some time and under several methods of investigation. An exception is a reduction of the Black-White IQ difference on the intelligence portion of the K-ABC to about .5 standard deviations, although this result is controversial and poorly understood (see Kamphaus & Reynolds, 1987, for a discussion). In addition, such findings are consistent only for African Americans. Other, highly diverse findings appear for native African and other Black populations (Jensen, 1980).

Researchers have taken into account a number of demographic variables, most notably socioeconomic status (SES). The size of the mean Black-White difference in the United States then diminishes to .5-.7 standard deviations (Jensen, 1980; Kaufman, 1973; Kaufman & Kaufman, 1973; Reynolds & Gutkin, 1981) but is robust in its appearance.

Asian groups, although less thoroughly researched than Black groups, have consistently performed as well as or better than Whites (Pintner, 1931; Tyler, 1965; Willerman, 1979). Asian Americans obtain average mean ability scores (Flynn, 1991; Lynn, 1995; Neisser et al., 1996; Reynolds, Willson, & Ramsay, 1999).

Matching is an important consideration in studies of ethnic differences. Any difference between groups may be due neither to test bias nor to ethnicity but to SES, nutrition, and other variables that may be associated with test performance. Matching on these variables controls for their associations.

A limitation to matching is that it results in regression toward the mean. Black respondents with high self-esteem, for example, may be selected from a population with low self-esteem. When examined later, these respondents will test with lower self-esteem, having regressed to the lower mean of their own population. Their extreme scores—high in this case—were due to chance.

Clinicians and research consumers should also be aware that the similarities between ethnic groups are much greater than the differences. This principle holds for intelligence, personality, and most other characteristics, both psychological and physiological. From another perspective, the variation among members of any one ethnic group greatly exceeds the differences between groups. The large similarities among groups appear repeatedly in statistical analyses as large, statistically significant constants and great overlap between different groups' ranges of scores.

Some authors (e.g., Schoenfeld, 1974) have disputed whether racial differences in intelligence are real or even re-searchable. Nevertheless, the findings are highly reliable from study to study, even when study participants identify their own race. Thus, the existence of these differences has gained wide acceptance. The differences are real and undoubtedly complex. The tasks remaining are to describe them thoroughly (Reynolds, Lowe, et al., 1999) and, more difficult, to explain them in a causal sense (Ramsay, 1998a, 2000). Both the lower scores of some groups and the higher scores of others must be explained, and not necessarily in the same way.

Over time, exclusively genetic and environmental explanations have lost so much of their credibility that they can hardly be called current. Most researchers who posit that score differences are real now favor an interactionist perspective. This development reflects a similar shift in psychology and social science as a whole. However, this relatively recent consensus masks the subtle persistence of an earlier assumption that test score differences must have either a genetic or an environmental basis. The relative contributions of genes and environment still provoke debate, with some authors seemingly intent on establishing a predominantly genetic or a predominantly environmental basis. The interactionist perspective shifts the focus of debate from how much to how genetic and environmental factors contribute to a characteristic. In practice, not all scientists have made this shift.

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