This mega-size volume distills 18,000 studies into 1,920 tables across 950 extra large pages, with the references provided on a CD in an attached pocket. Over 11 years, the authors flagged all references to the words sex and gender in Current Contents, with an average of 50 to 70 new articles each week. The findings are organized in tables across 13 chapters: 1, Basic Biological Factors; 2, Brain and Biochemistry; 3, Health and Illness; 4, Perceptual, Motor, and Emotional Factors; 5, Intellectual, Self-Concept, and Mental Health Factors; 6, Preferences and Interests; 7, Stress-Related Responses including Drugs and Therapy; 8, Personality; 9, Social Behavior; 10, Consumer Behavior; 11, Work-Related Behavior; 12, Attitudes; and 13, General Summary.
Each table gives the references (Name, year) for those studies that show males are higher, for those showing females are higher, and also for those that show no significant differences. The tables are further divided where appropriate by age groups (infant, toddler, early childhood, adolescent, adult); geographical region (Africa, Asia, North America); and by species (10% of the studies are of non-human species). In the final chapter, the topics are revisited with tables that provide a Consistency Index (CI) based on the number of studies and proportion favoring a particular sex, a Diversity Index (DI) indicating the number of countries, cultures, and time periods covered, and a Generalization Statement based on the number of studies and the CI and DI, which states whether the sex difference is well-established, probable, possible, or not there.
What are some of the major findings? Males are born heavier and grow taller in adulthood. They have larger cranial capacities, greater muscular strength, are better at mechanical problem solving, and average higher in spatial reasoning ability and general knowledge. They are more active, exploratory, competitive, and aggressive; they are also more confident and report having more sex! Males also have more learning disabilities, more behavioral problems including crime and antisocial behavior, and die more often from accidents (for this latter, 75 studies, CI = 0.95).
Females are more careful and cautious; they have better fine motor skills than males and are friendlier, more confiding, and more care-giving. They are also more anxious, suffer more from stress, and are generally more emotional. Females like school better and get better grades (in this latter, 98 studies, CI = 0.75). Males however rate their own academic ability as higher (31 studies, CI = 0.65) and get higher college admission exam scores (48 studies, CI = 0.73). No overall IQ differences were found either pre- or post-puberty (207 studies, CI = 0.50), although males were found to be more variable (24 studies, CI = 0.79).
Some summary tables are less clear than ideal and highlight why meta-analyses of specific topics may be more useful with information provided on the factors which lead to larger or smaller effect sizes. For example, I have published research on the female advantage in empathy finding that the amount of variability in measuring instruments is correlated with the magnitude of the female advantage; if there is little variability in the measure, the sex difference is missed. Similarly Richard Lynn and Paul Irwing have found that when general ability IQ tests are examined after age 17, males score 4 IQ points higher than females. Such finer grain effects are missed in the kinds of tables presented here.
However, limitations aside, this tome is a fascinating collation of information. One tid-bit I discovered is that males do too like to shop more than women, at least when it comes to electronic gadgets! The book is chock-full of nuggets of information. For example, the sexes differ in numerous illnesses and causes of death. For the answer to what those differences might be, you'll have to read the book.
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