Foot problems as risk factors of fractures

This case-control study examines whether foot problems are risk factors of fractures of five sites among people aged 45 years or older at six Kaiser Permanente Medical Centers in northern California. From October 1996 to May 2001, interviewers collected information through a standardized questionnaire. Incident cases of distal forearm (n = 1,000), foot (n = 827), proximal humerus (n = 448), shaft of the tibia/fibula (n = 168), and pelvis (n = 172) fractures and 1,913 controls from the same medical centers were included. After adjustment for potential confounders and for each additional foot problem, the odds of a foot fracture increased by 8% (adjusted odds ratio = 1.08, 95% confidence interval: 1.03, 1.13). In contrast, each additional foot problem was associated with a reduction in the odds of a forearm fracture (adjusted odds ratio = 0.93, 95% confidence interval: 0.89, 0.98). In general, foot problems were not related to fractures of other sites, although diabetes, which may result in foot problems, increased the odds of a proximal humerus fracture (adjusted odds ratio = 1.65, 95% confidence interval: 1.20, 2.26). If these findings are supported by data from other studies, preventive measures to retard the development of foot problems could reduce the incidence of foot fractures.     

Increased falling as a risk factor for fracture among older women: the study of osteoporotic fractures

More frequent falling is associated with a higher risk of fracture among older women, but it is not known whether an increased rate of falling, independent of the average rate, also increases fracture risk. The authors examined the relation between an increase in the rate of falls during the first 4 years of follow-up and the subsequent fracture rate, reported for a median of 6.3 years (1986-1998), in 9,106 US women aged 65 years or more. Women in the upper quartile of increasing falls (>0.44 falls/year/year) had greater risks of subsequent hip fracture (rate ratio = 1.42, 95% confidence interval: 0.99, 2.04) and fracture of the proximal humerus (rate ratio = 1.79, 95% confidence interval: 1.08, 2.95) than women without an increase in falls, after adjustment for age, average rate of falls over 4 years, and known risk factors for fracture. Risks of distal forearm, ankle, or foot fracture were not elevated. The associations between fracture risk and increasing falls were not accounted for by baseline physical or cognitive function. An increase in the rate of falls, independent of the average rate, may be associated with a higher risk of frailty (hip and proximal humerus) fractures but not fractures at other sites.     

Risk factors for proximal humerus fracture

This case-control study of proximal humerus fracture included 448 incident female and male cases and 2,023 controls aged 45 years or older identified in five Northern California Kaiser Permanente Medical Centers in 1996-2001. Data were collected by using an interviewer-administered questionnaire. Some factors related to low bone mass, including number of fractures since age 45 years and low dietary calcium intake, were associated with increased risks of fracture, and factors thought to protect against bone loss, such as menopausal hormone therapy and calcium carbonate tablet use, were associated with reduced risks. Fall-related risk factors included previous falls, diabetes mellitus, and difficulty walking in dim light. Possible fall-related risk factors suggested for the first time in this study were seizure medication use (adjusted odds ratio (OR) = 2.80, 95% confidence interval (CI): 1.45, 5.42), depression (OR = 1.34, 95% CI: 0.98, 1.84), almost always using a hearing aid (OR = 1.92, 95% CI: 1.12, 3.31 vs. never prescribed), and left-handedness (OR = 2.36, 95% CI: 1.51, 3.68 vs. right-handedness). Difficulty with activities of daily living and lack of physical activity tended to be associated with increased risk. Prevention of falls among frail, osteoporotic persons would likely reduce the frequency of proximal humerus fracture.     

Risk factors for pelvis fracture in older persons

From 1996 to 2001, the authors undertook a case-control study of 192 pelvis fracture cases (men and women) and 2,402 controls aged > or = 45 years at five Kaiser Permanente medical centers in Northern California. Most information on potential risk factors was obtained by means of an interviewer-administered questionnaire. Number of fractures since age 45 years and a maternal history of hip fracture were associated with increased risks. Several factors thought to protect against loss of bone mass, including recent use of menopausal hormone therapy (adjusted odds ratio (OR) = 0.55, 95% confidence interval (CI): 0.33, 0.91) and high body mass index (weight (kg)/height (m)2; per 5-unit increase, adjusted OR = 0.65, 95% CI: 0.52, 0.81), were associated with decreased risks, while cigarette smoking (adjusted OR = 2.17, 95% CI: 1.34, 3.52) and hysterectomy (adjusted OR = 1.75, 95% CI: 1.15, 2.66) were associated with increased risks. Various conditions related to propensity to fall were associated with increased risks. Most indicators of frailty, including use of walking aids and needing help with or being unable to perform various activities of daily living, conferred increased risks. Thus, low bone mass, frailty, and probably a propensity to fall appear to be associated with increased risk of pelvis fracture.     

Reproductive history and postmenopausal risk of hip and forearm fracture

This case-control study was designed to investigate the relation between reproductive history and occurrence of hip and forearm fractures in postmenopausal women. Three hundred and fifty-five King County, Washington women who sustained a fracture between 1976 and 1980 and 562 control women were interviewed regarding their reproductive history and other factors. After controlling for the confounding effects of age, obesity, and use of noncontraceptive estrogens, the authors found that women who gave birth four or more times had a risk of fracture similar to women who had not given birth (odds ratio = 1.2, 95% confidence interval = 0.7-2.2), and women who breastfed for more than two years had a risk of fracture similar to women who had never breastfed (odds ratio = 0.8, 95% confidence interval = 0.4-1.5).     

Risk factors, falls, and fracture of the distal forearm in Manchester, UK.

OBJECTIVE: To determine the risk factors associated with fracture of the distal forearm, and to evaluate the influence of falls on these risks. DESIGN: This was a case-control study. SETTING: Manchester, UK. PARTICIPANTS: The cases were 62 white women aged 45-82 years who had sustained a fracture of the distal forearm and had attended local hospitals. Two control groups were studied - 50 women who had fallen onto the hand but had not sustained a fracture (recruited from the same source as those with fracture) and 116 women randomly selected from primary care age and sex registers in the catchment area of the hospitals. Both cases and controls were sent a letter inviting them to take part in the study. Data were collected by questionnaire completed by an interviewer. MAIN RESULTS: Compared with the population control group, those with fracture were more likely to walk at a brisk pace (odds ratio (OR) = 3.5; 95% confidence interval (CI) 1.3, 9.6) though they had undertaken less physical activity at home or work on a daily basis throughout life (OR = 0.4; 95% CI 0.2, 0.9). The risk associated with brisk walking was less marked when the cases were compared with fall controls. Other lifestyle factors including calcium intake, smoking, and alcohol consumption were not associated with fracture. Analysis of gynaecological and hormonal factors suggested that compared with population controls, those with fracture of the distal forearm had had fewer fertile years (OR = 0.4; 95% CI 0.1, 0.9) and were less likely to have used oral contraceptives (OR = 0.3; 95% CI 0.1, 0.9). CONCLUSIONS: The data highlight the need for caution when advising middle aged and elderly subjects about exercise. Such advice should be combined with practical information about the prevention of falls. Hormonal factors seem to be additional determinants of fracture. Other lifestyle interventions seem unlikely to play an important part in preventing distal forearm fracture.     

Milk, dietary calcium, and bone fractures in women: a 12-year prospective study.

OBJECTIVES: This study examined whether higher intakes of milk and other calcium-rich foods during adult years can reduce the risk of osteoporotic fractures. METHODS: This was a 12-year prospective study among 77761 women, aged 34 through 59 years in 1980, who had never used calcium supplements. Dietary intake was assessed with a food-frequency questionnaire in 1980, 1984, and 1986. Fractures of the proximal femur (n = 133) and distal radius (n = 1046) from low or moderate trauma were self-reported on biennial questionnaires. RESULTS: We found no evidence that higher intakes of milk or calcium from food sources reduce fracture incidence. Women who drank two or more glasses of milk per day had relative risks of 1.45 for hip fracture (95% confidence interval [CI] = 0.87, 2.43) and 1.05 for forearm fracture (95% CI = 0.88, 1.25) when compared with women consuming one glass or less per week. Likewise, higher intakes of total dietary calcium or calcium from dairy foods were not associated with decreased risk of hip or forearm fracture. CONCLUSIONS: These data do not support the hypothesis that higher consumption of milk or other food sources of calcium by adult women protects against hip or forearm fractures.     

Is radiographic vertebral fracture a risk factor for mortality?

Clinical fractures predict increased mortality risk, but few studies report mortality based on prevalent radiographically defined vertebral fracture. This study examined whether radiographically defined vertebral fracture is a risk factor for mortality in older adults. The 1,580 participants in California (631 men, 949 women) were aged > or =50 years in 1992-1996. Lateral spine radiographs, and information about medical history and behaviors, were obtained. Overall, 55 (8.7%) men and 123 (13%) women had at least one prevalent fracture at baseline; of these, 48 women and 14 men had two or more. Over 7.6 years, 460 participants died, 27.6% without and 41.0% with prevalent fractures (p < 0.001). Prevalent vertebral fracture was not associated with all-cause mortality in both sexes combined (adjusted hazard ratio = 1.09, 95% confidence interval: 0.84, 1.42) or sex-specific analyses (women: adjusted hazard ratio = 1.15, 95% confidence interval: 0.83, 1.59; men: adjusted hazard ratio = 0.89, 95% confidence interval: 0.55, 1.46). However, women with two or more prevalent fractures had increased risk of all-cause mortality (adjusted hazard ratio = 1.56, 95% confidence interval: 1.01, 2.40; p = 0.04). Women with any prevalent vertebral fractures also had increased mortality risk from "other" causes (adjusted hazard ratio = 1.59, 95% confidence interval: 1.03, 2.45; p = 0.04) but not cardiovascular disease or cancer. A single radiographic vertebral fracture is not a risk for mortality in older women; larger, longer studies of men and those with two or more radiographic vertebral fractures are needed.     

Fall frequency and incidence of distal forearm fracture in the UK.

STUDY OBJECTIVE--This analysis aimed to determine the frequency of falls in men and women aged 50 years and over and to explore whether age variation in fall frequency may explain variation in the incidence of distal forearm fracture in women. DESIGN--This was a cross sectional survey. SETTING--Primary care based registers in four UK areas. PARTICIPANTS--Altogether 501 men and 702 women age 50-79 years participated. MAIN RESULTS--A total of 131 (26.1%) men and 181 (25.8%) women reported falling in the previous year. In women, the frequency of falls rose with age (chi 2 test for trend 4.33; p = 0.04), with no obvious early post-menopausal peak or subsequent decline. Men aged 50-54 years had a significantly increased risk of falls compared with women of this same age group, (odds ratio (OR) = 2.4; 95% confidence interval (CI) 1.3, 4.6), though above this age, the risk of falling was greater in women (OR = 1.2; 95% CI 0.9, 1.5). CONCLUSION--There are important differences in the frequency of falls in relation to age and sex. The data suggest that variation in fall frequency per se does not explain age variation in the incidence of distal forearm fracture in women.     

The effect of hip fracture on mortality, hospitalization, and functional status: a prospective study.

OBJECTIVES: The purpose of this study was to prospectively assess the independent effect of hip fracture on mortalìty, hospitalization, and functional status. METHODS: Among 7527 members of the Longitudinal Study of Aging who were over age 70 at baseline, 368 persons with hip fracture occurring between 1984 and 1991 were identified. Median length of follow-up was 831 days. RESULTS: Hip fracture was significantly related to mortality (adjusted hazards ratio [AHR] = 1.83; 95% confidence interval [CI] = 1.55, 2.16) when treated as a time-dependent covariate. This effect was concentrated in the first 6 months postfracture (AHR = 38.93, 95% CI = 29.58, 51.23, vs AHR = 1.17; 95% CI = 0.95, 1.44). Hip fracture significantly increased the likelihood of subsequent hospitalization (adjusted odds ratio = 3.31, 95% CI = 2.64, 4.15) and increased the number of subsequent episodes by 9.4%, the number of hospital days by 21.3%, and total charges by 16.3%. Hip fracture also increased the number of functional status dependencies. CONCLUSIONS: The health of older adults deteriorates after hip fracture, and efforts to reduce the incidence of hip fracture could lower subsequent mortality, morbidity, and health services use.     

Associations between fracture incidence and use of depot medroxyprogesterone acetate and anti-epileptic drugs in women with developmental disabilities

PURPOSE: We sought to evaluate any association between incidence of osteoporotic fractures and use of depot medroxyprogesterone acetate (DMPA) and/or anti-epileptic drugs (AEDs) among women and girls with developmental disabilities. METHODS: Cross-sectional population-based observational study of all noninstitutionalized females with developmental disabilities age >/=13 who received fee-for-service Medicaid in Washington State during 2002 (n = 6,773), using administrative data. MAIN FINDINGS: In a sample of 6,773 females, 140 women (2%) had an osteoporotic fracture during 2002. Among 340 users of DMPA, 13 (3.8%) had an osteoporotic fracture with an odds ratio of 2.4 (95% confidence interval [CI], 1.3-4.4) for fracture compared to nonusers. Among 1,909 users of AEDs, 60 (3.1%) had an osteoporotic fracture with an odds ratio of 1.9 (95% CI, 1.3-2.6) for fracture compared to nonusers. We controlled for use of drugs (DMPA or AEDs), age and race (as white or other racial and ethnic groups). CONCLUSIONS: Use of either AEDs or DMPA by women with developmental disabilities is associated with significantly increased incidence of fracture. Women and girls who have developmental disabilities may be poor candidates for DMPA use owing to increased risk of fractures. Further research is indicated to 1) determine the specific risks profile of DMPA for this population, 2) explore alternative means of managing significant menstrual problems and contraceptive needs in this population, and 3) screen current and previous users of DMPA and chronic users of AEDs for osteoporosis risk, regardless of age.     

The gender- and age-specific 10-year and lifetime absolute fracture risk in Tromsø, Norway

Aim of this study is to estimate the gender- and age-specific 10-year and lifetime absolute risks of non-vertebral and osteoporotic (included hip, distal forearm and proximal humerus) fractures in a large cohort of men and women. This is a population-based 10 years follow-up study of 26,891 subjects aged 25 years and older in Tromsø, Norway. All non-vertebral fractures were registered from 1995 throughout 2004 by computerized search in radiographic archives. Absolute risks were estimated by life-table method taking into account the competing risk of death. The absolute fracture risk at each year of age was estimated for the next 10 years (10-year risk) or up to the age of 90 years (lifetime risk). The estimated 10-year absolute risk of all non-vertebral fracture was higher in men than women before but not after the age of 45 years. The 10-year absolute risk for non-vertebral and osteoporotic fractures was over 10%, respectively, in men over 65 and 70 years and in women over 45 and 50 years of age. The 10-year absolute risks of hip fractures at the age of 65 and 80 years were 4.2 and 18.6% in men, and 9.0 and 24.0% in women, respectively. The risk estimates for distal forearm and proximal humerus fractures were under 5% in men and 13% in women. The estimated lifetime risks for all fracture locations were higher in women than men at all ages. At the age of 50 years, the risks were 38.1 and 24.8% in men and 67.4 and 55.0% in women for all non-vertebral and osteoporotic fractures, respectively. The estimated gender- and age-specific 10-year and lifetime absolute fracture risk were higher in Tromsø than in other populations. The high lifetime fracture risk reflects the increased burden of fractures in this cohort.     

Exposure to natural fluoride in well water and hip fracture: a cohort analysis in Finland.

In the retrospective cohort study based on record linkage, the authors studied a cohort of persons born in 1900-1930 (n = 144,627), who had lived in the same rural location at least from 1967 to 1980. Estimates for fluoride concentrations (median, 0.1 mg/liter; maximum, 2.4 mg/liter) in well water in each member of the cohort were obtained by a weighted median smoothing method based on ground water measurements. Information on hip fractures was obtained from the Hospital Discharge Registry for 1981-1994. No association was observed between hip fractures and estimated fluoride concentration in the well water in either men or women when all age groups were analyzed together. However, the association was modified by age and sex so that among younger women, those aged 50-64 years, higher fluoride levels increased the risk of hip fractures. Among older men and women and younger men, no consistent association was seen. The adjusted rate ratio was 2.09 (95% confidence interval: 1.16, 3.76) for younger women who were the most exposed (>1.5 mg/liter) when compared with those who were the least exposed (< or =0.1 mg/liter). The results suggest that fluoride increases the risk of hip fractures only among women.     

Association of total calcium and dietary protein intakes with fracture risk in postmenopausal women: The 1999–2002 National Health and Nutrition Examination Survey (NHANES)

ObjectiveWe examined the associations of total calcium intake (TCI) and dietary protein intake (DPI) with risk of fracture.MethodsA total of 2006 postmenopausal women ≥50 y of age who were measured in the 1999–2002 National Health and Nutrition Examination Survey were included in the study. Weighted mean TCI and DPI and percentage of distributions of selected characteristics were estimated by TCI category and fracture status. Multivariate logistic regression models were used to assess the effect of TCI and DPI on risk of fracture.ResultsThirteen percent of participants reported a fracture history, of whom 17.8% consumed a total of ≥1200 mg of calcium per day and 23.8% consumed <400 mg/d. TCI was not associated with fracture risk when controlling for all selected covariates. In women who consumed <46 g/d of dietary protein, those with a TCI ≥1200 mg/d had a significantly higher risk of fracture than those with the lowest TCI (adjusted odds ratio 5.98, 95% confidence interval 1.15–31.13), whereas in women who consumed >70 g/d of dietary protein, those with a TCI ≥1200 mg/d had an insignificant lower risk of fracture (adjusted odds ratio 0.69, 95% confidence interval 0.20–2.39).ConclusionTCI is not associated with risk of fracture among postmenopausal women. Adequate TCI in the presence of inadequate DPI may not be protective against fractures. Optimal proportion of TCI and DPI warrants further investigation among older women.     

Fracture risk in the U.S. Medicare population

Using data from the 5% U.S. Medicare sample, we estimated the actuarial (life table) risk that a person aged 65 will fracture the upper or lower limbs or the pelvis, by age 75, 80, 85, and 90, taking into account the chance of dying in the interval. The actuarial risk of a 65-year old white woman sustaining a fracture by age 90 is 16% for the hip, 9% for distal forearm, 5% for proximal humerus, and 4% for ankle. Black women and white men have substantially lower risks, and the risks for black men are very low. Although hip fractures pose the single greatest risk, the risk of all other fractures combined is greater. White women have particularly high risks for all fractures, because of their longevity as well as their high fracture rates. It is important to adjust for the probability of dying when estimating risks in an elderly population.     

High-fat, low-carbohydrate diet and the etiology of non-insulin-dependent diabetes mellitus: the San Luis Valley Diabetes Study

Diet has long been believed to be an important risk factor for non-insulin-dependent diabetes. Animal studies generally support a relation between high-fat diets and development of insulin resistance. However, conclusive epidemiologic evidence is lacking. To further investigate the role of dietary fat and carbohydrate as potential risk factors for the onset of non-insulin-dependent diabetes mellitus, current diet was assessed among a geographically based group of 1,317 subjects without a prior diagnosis of diabetes who were seen in the period from 1984 to 1988 in two countries in southern Colorado. In this study, 24-hour diet recalls were reported prior to an oral glucose tolerance test. Persons with previously undiagnosed diabetes (n = 70) and impaired glucose tolerance (n = 171) were each compared with confirmed normal controls (n = 1,076). The adjusted odds ratios relating a 40-g/day increase in fat intake to non-insulin-dependent diabetes mellitus and impaired glucose tolerance were 1.51 (95% confidence interval 0.85-2.67) and 1.62 (95% confidence interval 1.09-2.41), respectively. Restricting cases to diabetic persons with fasting glucose greater than 140 mg/dl and persons with impaired glucose tolerance confirmed on follow-up, the odds ratios increased to 3.03 (95% confidence interval 1.07-8.62) and 2.67 (95% confidence interval 1.33-5.36), respectively. The findings support the hypothesis that high-fat, low-carbohydrate diets are associated with the onset of non-insulin-dependent diabetes mellitus in humans.     

Weight cycling and risk of forearm fractures: a 28-year follow-up of men in the Oslo Study

Weight cycling may lead to fractures in non-weight-bearing bone. The authors investigated the association between self-reported episodes of weight loss and forearm fracture in a cohort of elderly Norwegian men (n = 4,601; mean age = 71.6 years). Men initially examined in 1972-1973 as part of the population-based Oslo Study were reexamined in 2000. Weight and height were measured both times; histories of weight cycling (amount and frequency) and fracture and information on covariates were elicited by questionnaire. Irrespective of amount of weight loss, 35-43% of men reporting four or more weight loss episodes at ages 25-50 years had experienced a forearm fracture, as compared with 17-18% of men without weight loss episodes. For weight loss episodes that had occurred after age 50 years, associations were weaker. In an analysis limited to men whose last fracture had occurred after the weight loss episodes, the adjusted odds ratio for forearm fracture was 2.91 (95% confidence interval: 1.10, 7.64) for four or more weight loss episodes versus none. These findings suggest that weight cycling may predict forearm fracture in elderly men and indicate that the potentially harmful effects of weight cycling are related to the number of episodes occurring at ages 25-50 years.     

Dietary fat intake and the risk of osteoporotic fractures in the elderly

OBJECTIVE: To explore the association between fat intake, serum lipids and the risk of osteoporotic fractures in the elderly. DESIGN: A hospital-based case-control study. SETTING: The study was conducted at a tertiary centre and referral hospital for the province of Jaén (Spain). SUBJECTS: Cases (n=167) were patients aged 65 years or more with a low-energy fracture selected from the population attended at the hospital. Controls (patients without antecedents of any fracture) were 1:1 matched to cases by sex and age (n=167). METHODS: Diet was assessed by a semiquantitative food frequency questionnaire. Serum total cholesterol and high-density lipoprotein (HDL) cholesterol were also measured. RESULTS: Participants in the two upper quartiles of polyunsaturated fat (PUFA) intake showed an increased risk of fracture, with statistically significant differences with respect to the first quartile in the adjusted model (odds ratio (OR)=3.59; 95% confidence interval (CI)=1.06-12.1 and OR=5.88; 95% CI=1.38-25.02); P=0.01 for the trend test). A higher ratio of monounsaturated fat (MUFA) to PUFA was associated with a reduced risk of fracture (OR=0.20; 95% CI=0.07-0.60 for the fourth quartile; P=0.002 for the trend test). The intake of omega-6 fatty acids was associated with an elevated risk of fracture (OR=3.41; 95% CI=1.05-11.15 for the fourth quartile; P=0.01 for the trend test). HDL-cholesterol levels were inversely associated with the risk of fracture (test for trend P=0.03 across quartiles). CONCLUSIONS: PUFA intake was associated with an increased risk of osteoporotic fractures in the elderly, whereas a high ratio of MUFA:PUFA was associated with decreased risk.     

Violence and psychiatric morbidity in a national household population--a report from the British Household Survey

This study measured the prevalence of self-reported violence and associations with psychiatric morbidity in a national household population, based on a cross-sectional survey in 2000 of 8,397 respondents in Great Britain. Diagnoses were derived from computer-assisted interviews, with self-reported violent behavior over the previous 5 years. The 5-year prevalence of nonlethal violence in Britain was 12% (95% confidence interval: 11, 13). The risk of violence was substantially increased by alcohol dependence (odds ratio=2.72, 95% confidence interval: 1.85, 3.98), drug dependence (odds ratio=2.63, 95% confidence interval: 1.45, 4.74), and antisocial personality disorder (odds ratio=6.12, 95% confidence interval: 3.87, 9.66). Low prevalences of these conditions (7%, 4%, and 4%, respectively) contrasted with their relatively high proportions of attributed risk of violence (23%, 15%, and 15%). Hazardous drinking was associated with 56% of all reported violent incidents. Screening positive for psychosis did not independently increase risk (odds ratio=3.20, 95% confidence interval: 0.35, 29.6). The study concluded that psychiatric morbidity makes a significant public health impact on violence exerted primarily by persons with any personality disorder, substance dependence, and hazardous drinking. Population interventions for violent behavior are appropriate for hazardous drinking as are targeted interventions for substance dependence and antisocial personality disorder. Despite public concern, the risks of violence from persons with severe mental illness were very low.     

Black-white differences in fracture rates.

To compare the incidence of all nonvertebral fractures between elderly blacks and whites, the authors conducted a retrospective cohort study among Tennessee Medicaid enrollees aged 65 years or more from 1987 through 1989. A previously validated computer algorithm identified 6,802 persons of black or white race with 7,645 new nonvertebral fractures. The incidence of all nonvertebral fractures in blacks was only half of that in whites. This finding persisted after the authors controlled for sex, age, and nursing home residence (relative risk = 0.4, 95% confidence interval 0.4-0.5). Rates were consistently lower among blacks within subgroups defined by these factors and for each of the 13 different fracture sites examined. The magnitude of the difference between blacks and whites in rates of all fractures combined and most site-specific fractures is similar to that previously reported for hip fractures. These consistent racial differences suggest a common underlying factor(s).