Most research indicates that mortality rates during extreme heat vary with age, sex, and race. In the chapter "Climate Effects on Human Health" of the Environmental Protection Agency's 1987 monograph Potential Effects of Future Climate Changes, Kalkstein and Valimont (1987) cite many of the studies from the 1970s and 1980s that examine specific risk factors contributing to heat-related deaths. White and Hertz-Picciotto (1985) also summarize this research, including a discussion of how heat accelerates certain pre-existing diseases and conditions, in the section "Human Health" of the Department of Energy's 1985 report Characterization of Information Requirements for Studies of CO2 Effects. The authors report that although researchers generally agree older members of an exposed population are at higher risk, not as many agree about the vulnerability of infants. Fewer studies have considered this risk group, however. In addition, White and Hertz-Picciotto relate that researchers conflict on the role of gender in mortality rates and strongly disagree on the role of race. They report that some researchers attribute increased mortality to socioeconomic factors rather than race. White and Hertz-Picciotto also refer to several studies that indicate increased heat-related death rates for residents of inner cities compared with populations in suburban and rural districts. Some authors maintain this increase may be due to the "urban heat island" effect compounded by fewer air-conditioners and other socioeconomic differences.