The adage that a picture is worth a thousand words may hold true for textbooks.

Research presented Saturday in San Francisco at the annual meeting of the American Psychological Association explored how students evaluate textbooks and the factors that make them more or less likely to read textbooks. The research was designed to build on studies that have previously found many students who skip buying textbooks and many others who buy and don't read -- despite evidence showing that careful readers of textbooks earn higher grades.

The study was based on surveys of 230 undergraduates in an introductory psychology course at a Midwestern university. The courses were not identified further except to say that they were not courses taught by the authors of the paper, Regan A.R. Gurung, an associate professor of psychology at the University of Wisconsin at Green Bay, and Ryan Martin, an assistant professor there.

Their findings:

Four factors (not all of which professors can control) best predicted whether students would spend more time with the textbook: gender of the students, the quality of visuals and the quality of photographs in the books, and the extent to which professors link assigned textbook sections to lectures and other in-class work.

On gender, women are more likely than men to read. On the link between professors' use of classtime and students choices, the study found that unless faculty members are explicit about the importance of students reading the text, many won't do so.

The significance of these findings, the professors write in their paper, is that faculty members need to move beyond an assumption that writing quality is the key way to evaluate textbooks. When writing quality is high, students who read the textbook appear to have benefited with a correlation in predicted exam scores. But it was the other, visual qualities, that led students to make the decision to spend more time with the text.