Refer to Table 2, which shows the main results of the study, adjusted for age (age-adjusted HR), and adjusted for several additional variables (multivariable HR). Using the cases and person-years shown, calculate the incidence rate for uterine cancer among women in each of the three exposure categories for hair relaxer use (Never/light, moderate, and heavy). Show your work, and express your answers as āper 100,000 person-years at riskā.
Table 2 Hazard ratios (95% confidence intervals for uterine cancer in relation to hair relaxer use, 1997-2019.
Person-years N cases Age-adjusted HR (95% CI) Multivariable HR (95% CI) Hair relaxer use Never/light 86,446 Moderate 458,424 Heavy 317,637 Duration of use Never/light 86,446 14 years 34,687 59 years 90,926 1014 years 186,663 1519 years 198,391 20 years 265,394 Frequency of useb Never/light 86,446 1-2 times/year 57,533 3-4 times/year 221,857 5-6 times/year 232,257 7 times/year 258,866 Age at first use <10 years 47,997 1019 years 475,060 2029 years 204,976 30 years 45,512 Number of burnsb c Never 119,074 burned 1-2 times 211,841 3-4 times 169,247 5-9 times 110,674 10 times 162,054
38 187 122 1.00 (ref) 1.18 (0.83, 1.68) 1.02 (0.71, 1.48) 1.00 (ref) 1.23 (0.86, 1.76) 1.18 (0.81, 1.71) 38 15 29 58 54 153 1.00 (ref) 1.03 (0.56, 1.87) 1.01 (0.62, 1.64) 1.24 (0.82, 1.88) 0.98 (0.64, 1.49) 1.16 (0.81, 1.65) 1.00 (ref) 1.00 (0.55, 1.83) 1.00 (0.61, 1.64) 1.35 (0.88, 2.06) 1.06 (0.69, 1.63) 1.28 (0.89, 1.84) 38 29 1.00 (ref) 1.19 (0.74, 1.94) 1.00 (ref) 1.22 (0.75, 2.00) 110 1.23 (0.85, 1.78) 1.25 (0.86, 1.83) 89 1.09 (0.74, 1.59) 1.23 (0.83, 1.81) 77 0.96 (0.64, 1.42) 1.08 (0.72, 1.61) 10 134 135 30 1.18 (0.55, 2.50) 1.11 (0.71, 1.73) 1.35 (0.89, 2.04) 1.00 (ref) 1.19 (0.56, 2.54) 1.13 (0.72, 1.78) 1.42 (0.93, 2.15) 1.00 (ref) 51 1.00 (ref) 1.00 (ref) 101 56 42 54 1.33 (0.95, 1.86) 0.98 (0.67, 1.44) 1.25 (0.83, 1.89) 1.10 (0.74, 1.62) 1.32 (0.94, 1.86) 0.97 (0.66, 1.43) 1.29 (0.85, 1.96) 1.08 (0.73, 1.61)
Never or light use is defined as 14 years, 2 times/year; heavy use is defined as >15 years, >5 times/year; remainder are moderate users (14 years, >3 times/ HR, hazard ratio; CI, confidence interval. HRs adjusted for age, period, menopause status pre, post, education 16 13-15, <12 years, physical activity none, <5, 5 h per week, parity no children, 1 child, 2 children, >3 children), smoking status (never, past, current), body mass index (continuous), alcohol consumption (<1, 1-6, or >7 drinks per week, oral contraceptive use 5 years, <5 years, never, age of menarche (14, 13, 12, 11 years), residential region (Northeast, South, Midwest, West), female hormone use (progestin alone or unknown, estrogen plus progestin but never estrogen alone, estrogen alone, never hormone use. b Frequency of use was missing for 4 cases; the number of burns was missing for 5 cases. Analyses exclude never/light users.