Noise exposure and hearing loss among sand and gravel miners

The objectives of this study were to describe workplace noise exposures, risk factors for hearing loss, and hearing levels among sand and gravel miners, and to determine whether full shift noise exposures resulted in changes in hearing thresholds from baseline values. Sand and gravel miners (n = 317) were interviewed regarding medical history, leisure-time and occupational noise exposure, other occupational exposures, and use of hearing protection. Audiometric tests were performed both before the work shift (following a 12-hour noise-free interval) and immediately following the work shift. Full shift noise dosimetry was conducted. Miners' noise exposures exceeded the Recommended Exposure Limit (REL) of the National Institute for Occupational Safety and Health (NIOSH) for 69% of workers, and exceeded the Mine Safety and Health Administration's action level for enrollment in a hearing conservation program for 41% of workers. Significantly higher noise exposures occurred among employees of small companies, among workers with a job classification of truck driver, among males, and among black workers. Hearing protection usage was low, with 48% of subjects reporting that they never used hearing protection. Hearing impairment, as defined by NIOSH, was present among 37% of 275 subjects with valid audiograms. Black male workers and white male workers had higher hearing thresholds than males from a comparison North Carolina population unexposed to industrial noise. Small but statistically significant changes in hearing thresholds occurred following full shift noise exposure among subjects who had good hearing sensitivity at baseline. In a logistic regression model, age and history of a past noisy job were significant predictors of hearing impairment. Overall, sand and gravel workers have excessive noise exposures and significant hearing loss, and demonstrate inadequate use of hearing protection. Well-designed hearing conservation programs, with reduction of noise exposure, are clearly needed.     

Predictors of hearing threshold levels and distortion product otoacoustic emissions among noise exposed young adults

Aim: To examine the relations between noise exposure and other risk factors with hearing function as measured by audiometric thresholds and distortion product otoacoustic emissions.

Methods: A total of 456 subjects were studied (393 apprentices in construction trades and 63 graduate students). Hearing and peripheral auditory function were quantified using standard, automated threshold audiometry, tympanometry, and distortion product otoacoustic emissions (DPOAEs). The analysis addressed relations of noise exposure history and other risk factors with hearing threshold levels (HTLs) and DPOAEs at the baseline test for the cohort.

Results: The cohort had a mean age of 27 (7) years. The construction apprentices reported more noise exposure than students in both their occupational and non-occupational exposure histories. A strong effect of age and years of work in construction was observed at 4, 6, and 8 kHz for both HTLs and DPOAEs. Each year of construction work reported prior to baseline was associated with a 0.7 dB increase in HTL or 0.2 dB decrease DPOAE amplitude. Overall, there was a very similar pattern of effects between the HTLs and DPOAEs.

Conclusions: This analysis shows a relatively good correspondence between the associations of noise exposures and other risk factors with DPOAEs and the associations observed with pure-tone audiometric thresholds in a young adult working population. The results provide further evidence that DPOAEs can be used to assess damage to hearing from a variety of exposures including noise. Clarifying advantages of DPOAEs or HTLs in terms of sensitivity to early manifestations of noise insults, or their utility in predicting future loss in hearing will require longitudinal follow up.

     

Prospective noise induced changes to hearing among construction industry apprentices

Aims: To characterise the development of noise induced damage to hearing.

Methods: Hearing and noise exposure were prospectively monitored among a cohort of newly enrolled construction industry apprentices and a comparison group of graduate students, using standard pure tone audiometry and distortion product otoacoustic emissions (DPOAEs). A total of 328 subjects (632 ears) were monitored annually an average of 3.4 times. In parallel to these measures, noise exposure and hearing protection device (HPD) use were extensively monitored during construction work tasks. Recreational/non-occupational exposures also were queried and monitored in subgroups of subjects. Trade specific mean exposure L_eq levels, with and without accounting for the variable use of hearing protection in each trade, were calculated and used to group subjects by trade specific exposure level. Mixed effects models were used to estimate the change in hearing outcomes over time for each exposure group.

Results: Small but significant exposure related changes in DPOAEs over time were observed, especially at 4 kHz with stimulus levels (L1) between 50 and 75 dB, with less clear but similar patterns observed at 3 kHz. After controlling for covariates, the high exposure group had annual changes in 4 kHz emissions of about 0.5 dB per year. Pure tone audiometric thresholds displayed only slight trends towards increased threshold levels with increasing exposure groups. Some unexpected results were observed, including an apparent increase in DPOAEs among controls over time, and improvement in behavioural thresholds among controls at 6 kHz only.

Conclusions: Results indicate that construction apprentices in their first three years of work, with average noise exposures under 90 dBA, have measurable losses of hearing function. Despite numerous challenges in using DPOAEs for hearing surveillance in an industrial setting, they appear somewhat more sensitive to these early changes than is evident with standard pure tone audiometry.

     

Hearing loss and perceptions of noise in the workplace among rural Australians

OBJECTIVE: To compare measured hearing levels of individuals regularly exposed to noise in their workplace to self-reported and family-reported hearing loss. To compare the attitudes and preventative actions adopted by individuals who are more aware of the potential for hearing loss to less aware individuals. DESIGN: The project examined the perceptions of rural workers concerning noise, noise exposure and hearing. The subjects completed a 'Noise at Work' questionnaire and some demographic data at the time of audiometric testing. SETTING: The subjects were recruited when attending their rural health clinic for audiometric testing. PARTICIPANTS: Participants comprised 113 men and 23 women (20-65 years, mean = 39.6, SD = 11.4) working across a range of activities at different levels in their workplaces. The range in current employment was from 0.5 to 45 years (mean = 13.8, SD = 10.7). RESULTS: Hearing tests were compared with perceptions of noise annoyance, hearing damage risk and preventative action. Self- and family-reported hearing loss and conversational difficulties in noise correlated well with measured audiograms. Perceptions of workplace noise tended to be more positive if people felt they had hearing problems. There was no difference in preventative action between those who did and did not feel they had hearing problems. Both groups rated barriers to action and lack of self-efficacy in a similar negative way. CONCLUSIONS: There is a need for specific training to ensure that rural workers have skills to take more positive action in reducing noise exposure at work.     

Hearing status among aircraft maintenance personnel in a commercial airline company

The aim was to study subjective and objective hearing loss in a population of aircraft maintenance workers and identify predictors. A total of 327 aircraft maintenance personnel answered a self-administered work environment questionnaire (response rate 76%) and underwent audiometric test. The mean values for the hearing threshold at 3, 4, and 6 kHz for the ear with the most hearing loss were compared with a Swedish population database of persons not occupationally exposed to noise. Equivalent noise exposure during a working day was measured. Relationships between subjective and objective hearing loss and possible predictors (age, years of employment, self-reported exposure to solvents, blood pressure, and psycho-social factors) were analyzed by multiple logistic regression. At younger ages (<40 years), aircraft maintenance workers had higher hearing thresholds (1-3 dB) compared to the reference group, but such a difference was not found in older employees. Relationships were found between age and objective hearing loss, and between exposure to solvents and reported subjective hearing loss. Equivalent noise exposure during working days were 70-91 dB(A) with a maximal noise level of 119 dB(A). Aircraft maintenance workers are exposed to equivalent noise levels above the Swedish occupational standard, including some very high peak exposures. Younger employees have a higher age-matched hearing threshold level compared with a reference group. Thus, there is a need for further preventive measures.     

Comparison of NIOSH noise criteria and OSHA hearing conservation criteria

BACKGROUND: This study was conducted to compare noise exposure measurements based on the recently revised noise exposure criteria recommended by the U.S. National Institute for Occupational Safety and Health (NIOSH) and the current U.S. Occupational Safety and Health Administration (OSHA) Hearing Conservation Amendment to the occupational noise standard. METHODS: Daily 8-hour time-weighted average (TWA) personal noise exposures were obtained for 61 workers using dosimeters set simultaneously to the NIOSH and OSHA Hearing Conservation Amendment (OSHA-HCA) criteria. A variety of work groups with the potential for noise exposure were evaluated as a part of this investigation. RESULTS: Noise dose based on the NIOSH criteria was higher than the corresponding OSHA-HCA noise dose with differences in noise exposures measured under the two criteria equal to 6.6 dBA. Should the new NIOSH recommendation on noise measurement be adopted as standard, the number of workers to be enrolled in a hearing loss prevention program was estimated to increase by 2. 7-fold from 23% to 75% of the study population. CONCLUSIONS: The results of this study indicate that if the NIOSH criteria are to be adopted as an OSHA standard, there is likely to be a substantial increase in the number of workers in hearing conservation programs.     

Program for hearing loss prevention in four metallurgical factories in Piracicaba, São Paulo, Brazil

This study analyzes noise control programs in four metallurgical factories in Piracicaba, S?o Paulo, Brazil. From 1997 to 2001, 741 workers were examined and the programs were analyzed based on workers' profiles (2,270 audiometric exams) and documents on hearing preservation programs. 41% of workers presented hearing loss (mean age 42.3; mean years of work 16.7). 104 workers with more than one audiometric exam presented changes in hearing threshold. 36.5% (38 workers) developed noise-induced hearing loss (NIHL) and 63.5% (66 workers) with existing NIHL showed worsening of their hearing threshold. In these factories, 69.5% of workers were exposed to > or = 84dB(A). We concluded that the hearing preservation programs are not adequately organized and that workers are still exposed to high noise levels at work, posing a risk for NIHL. In addition, the current legislation on hearing loss prevention is not enforced.     

Screening for beryllium disease among construction trade workers at Department of Energy nuclear sites

BACKGROUND: To determine whether current and former construction workers are at significant risk for occupational illnesses from work at the Department of Energy's (DOE) nuclear weapons facilities, screening programs were undertaken at the Hanford Nuclear Reservation, Oak Ridge Reservation, and the Savannah River Site. METHODS: Medical examination for beryllium disease used a medical history and a beryllium blood lymphocyte proliferation test (BeLPT). Stratified and multivariate logistic regression analyses were used to explore the risk of disease by age, race, sex, trade, duration of DOE employment, reported work in buildings where beryllium was used, and time since last DOE site employment. RESULTS: Of the 3,842 workers included in this study, 34% reported exposure to beryllium. Overall, 2.2% of workers had at least one abnormal BeLPT test, and 1.4% were also abnormal on a second test. Regression analyses demonstrated increased risk of having at least one abnormal BeLPT to be associated with ever working in a site building where beryllium activities had taken place. CONCLUSIONS: The prevalence of beryllium sensitivity and chronic beryllium disease (CBD) in construction workers is described and the positive predictive value of the BeLPT in a population with less intense exposure to beryllium than other populations that have been screened is discussed. The BeLPT findings and finding of cases of CBD demonstrate that some of these workers had significant exposure, most likely, during maintenance, repair, renovation, or demolition in facilities where beryllium was used.     

Hearing loss among older construction workers: Updated analyses

Background

A prior study of this construction worker population found significant noise‐associated hearing loss. This follow‐up study included a much larger study population and consideration of additional risk factors.

Methods

Data included audiometry, clinical chemistry, personal history, and work history. Qualitative exposure metrics for noise and solvents were developed. Analyses compared construction workers to an internal reference group with lower exposures and an external worker population with low noise exposure.

Results

Among participants (n = 19 127) an overall prevalence of hearing loss of 58% was observed, with significantly increased prevalence across all construction trades. Construction workers had significantly increased risk of hearing loss compared to reference populations, with increasing risk by work duration. Noise exposure, solvent exposure, hypertension, and smoking were significant risk factors in multivariate models.

Conclusions

Results support a causal relationship between construction trades work and hearing loss. Prevention should focus on reducing exposure to noise, solvents, and cigarette smoke.

     

Surveillance of respiratory diseases among construction and trade workers at Department of Energy nuclear sites

BACKGROUND: Medical screening programs were begun in 1996 and 1997 at three Department of Energy (DOE) nuclear weapons facilities (Hanford Nuclear Reservation, Oak Ridge, and the Savannah River Site) to evaluate whether current and former construction workers are at significant risk for occupational illnesses. The focus of this report is pneumoconiosis associated with exposures to asbestos and silica among workers enrolled in the screening programs through September 30, 2001. METHODS: Workers provided a detailed work and exposure history and underwent a respiratory examination, which included a respiratory history and symptom questionnaire, a posterior-anterior (P-A) chest radiograph, and spirometry. Both stratified and multivariate logistic regression analyses were used to explore the risk of disease by duration of DOE employment and frequency of exposure, while controlling for potential confounders such as age, race, sex, and other work in the construction and building trades. RESULTS: Of the 2602 workers, 25.2% showed one or more chest X-ray changes by ILO criteria and 42.7% demonstrated one or more pulmonary function defects. The overall prevalence of parenchymal changes by ILO criteria (profusion 1/0 or greater) was 5.4%. In the logistic regression models, the odds ratio for parenchymal disease was 2.6 (95% confidence interval (CI) = 1.0-6.6) for workers employed 6 to 20 years at Hanford or Savannah River and increased to 3.6 (95% CI = 1.1-11.6) for workers employed more than 35 years, with additional incremental risks for workers reporting routine exposures to asbestos or silica. CONCLUSIONS: Continued surveillance of workers is important given their increased risk of disease progression and their risk for asbestos related malignancies. Smoking cessation programs should also be high priority and continued abstinence for former smokers reinforced. Although the observed respiratory disease patterns are largely reflective of past exposures, these findings suggest that DOE needs to continue to review industrial hygiene control programs for work tasks involving maintenance, repair, renovation, and demolition.     

The effectiveness of hearing protection among construction workers

Effective hearing conservation programs in the construction industry are rare. Where programs are present, they often rely on workers' use of hearing protection devices (HPDs) rather than on exposure controls to reduce noise exposure levels. Dependence on HPDs for protection from high noise is problematic, as the protection provided by the HPD depends on both the HPD's attenuation level and the time the HPD is used. This article presents an analysis of data on noise exposure and hearing protection among construction workers drawn from several large datasets covering nine construction trades. A unique combination of 1-min dosimetry noise exposure levels and simultaneous self-reported use of HPDs was evaluated, as were occupational and nonoccupational HPD use data collected by questionnaire as part of a longitudinal study of noise exposure and hearing loss among apprentices. Direct measurements of HPD attenuation were also made on workers at their work site. The workers assessed in this study were found to use hearing protection less than one-quarter of the time that they were exposed above 85 dBA. Workers who reported always using HPDs in high noise on questionnaires were found to wear them only one-third of the time their exposures exceeded 85 dBA. Workers' self-reported use of HPDs during most noisy nonoccupational activities was also found to be low. Direct attenuation measurements found that workers were able to achieve more than 50% of the rated attenuation of their HPD on average, but that the variability in achieved attenuation was large. When the measured HPD attenuation levels and use time data were combined, the effective protection afforded by HPDs was less than 3 dB, a negligible amount given the high exposure levels associated with construction work. However, there was substantial variation in effective protection among the different trades assessed. These results demonstrate the need for better hearing conservation programs and expanded noise control efforts in the construction industry.     

Hearing loss in migrant agricultural workers

BACKGROUND: Farmers have high rates of hearing loss, yet little is known about the hearing status of migrant agricultural workers. We performed a cross-sectional survey to assess the prevalence and impact of hearing loss in this population. METHODS: One hundred fifty migrant and seasonal agricultural workers were surveyed at a series of health fairs held at migrant camps. A bilingual questionnaire included items related to hearing loss risk factors and subjective hearing difficulties. Pure tone audiometry and tympanometry were performed in a mobile testing van. RESULTS: More than half the subjects had some degree of hearing loss at audiometric frequencies between 500 and 6,000 Hz, especially in the higher frequencies. Hispanic males in the sample had significantly greater prevalence of high-frequency hearing loss compared to adults in the national Hispanic Health and Nutrition Examination Survey (HHANES). More than 35% of respondents complained of subjective difficulty hearing or understanding speech, yet no workers reported use of hearing aids. Even after adjusting for measured hearing loss, Hispanic farm workers were more likely than their English- speaking counterparts to complain of difficulty hearing or understanding speech, suggesting that language barriers could worsen the impact of hearing loss. Risk factors for hearing loss included age and abnormal tympanometry. Occupational exposures to noise from tractors and other machinery as well as pesticides were frequently reported, while use of hearing protection was rare. CONCLUSION: Hearing loss is a significant and under-recognized problem in the migrant worker population. Further preventive and treatment efforts are warranted.     

Hearing impairment among workers exposed to excessive levels of noise in ginning industries

Cotton ginning workers have a risk of hearing loss due to excessive noise levels at the workplace environment. In this study, estimates of typical sound levels prevailing at the workplace environment and its effects on hearing ability of the exposed workers were made among cotton ginning workers. Data on self-reported health status was collected by a questionnaire survey at 10 cotton ginning industries located at Jalgaon district of Maharashtra state, India. The cotton ginning workers were exposed to continuous noise levels between 89 and 106 dBA. The hearing ability of the subjects was accessed by pure tone audiometry. The results of audiometry show mild, moderate and moderately severe degree of hearing impairment among the cotton ginning workers. The data generated during the study show that hearing loss was significantly associated with period of exposure to the workplace noise (P <0.0001). The prevalence of audiometric hearing impairment defined as a threshold average greater than 25 dB hearing level was 96% for binaural low-frequency average, 97% for binaural mid frequency average and 94% for binaural high-frequency average in the cotton ginning workers. We recommend the compulsory use of personal protective equipment like ear plug by the cotton ginning workers at the workplace environment. A regular maintenance of ginning and pressing machineries will avoid the emission of excessive noise at the workplace environment of cotton gins. A regular periodic medical examination is necessary to measure the impact of workplace noise on the health of cotton ginning workers.     

Evaluation of the individual risk of hearing loss: prospective study

Summary A method is proposed to predict the individual risk of hearing impairment according to age, duration of exposure to noise and daily noise equivalent level. This method is based on the model described in the ISO proposed standard 1999 Determination of occupational noise exposure and estimation of noise-induced hearing impairment. The individual sensitivity to noise is defined as the percentage of the general population that would develop hearing losses lower than another person under the same conditions. This method is proposed in an attempt to upgrade industrial audiometric programs from hearing impairment detection programs to real hearing conservation programs.     

Development and pilot test of hearing conservation training for construction workers

BACKGROUND: Hearing conservation efforts in construction frequently rely on use of hearing protection devices (HPDs): however, training on HPDs is often not provided, and usage rates remain low. In this study, a hearing conservation training program was developed and pilot tested. METHODS: A theoretical model was selected as the basis for the program, and program contents and delivery methods were selected to optimize the effectiveness and flexibility of the training. Two evaluation measures were selected to assess training-related changes in self-reported HPD use. The first was a validated method using concurrent work-shift noise dosimetry, and the second was a survey concerning workers beliefs and attitudes towards HPDs and HPD use. RESULTS: The training program was pilot tested on a single construction site. Complete assessment data were available for 23 workers. The percent of time when hearing protection was used during noise levels above 85 dBA nearly doubled post-training, and the change was statistically significant. CONCLUSIONS: Pre- and post-training data from participating workers demonstrated that HPD use can be increased significantly with basic model-based training, even in industries with complex noise exposures such as construction.     

Hearing health of workers exposed to noise and insecticides

OBJECTIVE: To examine the peripheral auditory disorders in a group of workers exposed to organophosphate and pyrethroid insecticides, used in vector control campaigns. METHODS: The prevalence study examined a population of 98 individuals who sprayed insecticides in campaigns for the prevention of Dengue, Chagas disease and Yellow fever. The sampling approach was finalistic, and included the workers in a health district of Pernambuco, during the year 2000. A questionnaire was used to collect data on occupational and non-occupational risks, safety measures utilized, family history of auditory problems and health symptoms. Previous noise exposure history was also investigated, since noise can be a confounding factor for hearing loss. Hearing sensitivity and middle ear function were assessed by pure tone audiometry. RESULTS: Among those exposed to insecticides, 63.8% demonstrated a hearing loss. For the group of workers exposed to both noise and insecticides, hearing loss was observed in 66.7% of the cases. The median exposure time necessary to detect high-frequency losses was 3.4 years for workers exposed to both agents and 7.3 years for workers exposed to insecticides only. Hearing thresholds were poorest among workers exposed to both agents. Auditory damage for those with combined exposures to the two factors was more severe than the hearing losses observed among those exposed only to insecticides. CONCLUSIONS: There is evidence that exposure to insecticides was associated with peripheral sensorioneural hearing loss and that noise exposure can potentiate the ototoxic effects of insecticides. It is necessary to evaluate this possible association through epidemiological studies.     

Noise exposure and permanent hearing loss of textile workers in Thailand

Hearing loss induced by noise exposure in a large scale textile mill (number of workers = 1,611) in Thailand was investigated on the basis of interviews, noise measurements, and audiometric tests. The frequency of subjective symptoms relating to noise exposure was higher in the weavers than among other mill workers and office workers. The average noise levels in the weaving sections and other sections were 101.3 +/- 2.7 dBA and 89.8 +/- 5.3 dBA, respectively. The results of the audiometric tests revealed the significantly higher noise-induced hearing loss among workers in the weaving section compared to other mill workers and office workers (P less than 0.01). Among weavers, hearing levels decreased with the longer years of work. Concerning personal noise protective devices, 38.6% of the weavers never used them. It was concluded that hearing loss status in the workers of the mill was serious. Improvements by means of integrated work organization activities were recommended.     

Noise exposures aboard catcher/processor fishing vessels

BACKGROUND: Commercial fishing workers have extended work shifts and potential for 24 hr exposures to high noise. However, exposures in this industry have not been adequately characterized. METHODS: Noise exposures aboard two catcher/processors (C/P) were assessed using dosimetry, sound-level mapping, and self-reported activities and hearing protection device (HPD) use. These data were combined to estimate work shift, non-work, and 24 hr overall exposure levels using several metrics. The length of time during which HPDs were worn was also used to calculate the effective protection received by crew members. RESULTS: Nearly all workers had work shift and 24 hr noise levels that exceeded the relevant limits. After HPD use was accounted for, half of the 24 hr exposures remained above relevant limits. Non-work-shift noise contributed nothing to 24 hr exposure levels. HPDs reduced the average exposure by about 10 dBA, but not all workers wore them consistently. CONCLUSIONS: The primary risk of hearing loss aboard the monitored vessels comes from work shift noise. Smaller vessels or vessels with different layouts may present more risk of hearing damage from non-work periods. Additional efforts are needed to increase use of HPDs or implement noise controls.     

The effects of noise on hearing and oxidative stress in textile workers

The aim of this study was to investigate the effects of noise on hearing, lipid peroxidation and antioxidant enzymes in textile workers. Thirty textile workers exposed to high noise 105 dB (A) in a textile factory, and 30 healthy male volunteers in our hospital as a control group were included in the study. In both groups, following audiometric tests, blood samples were obtained. In these blood samples, Malonydialdehyte (MDA), Superoxide dismutase (SOD) and Catalase (CAT) levels were investigated. Statistical analysis was performed by using SPSS version 11.0 (SPSS Inc., Chicago 1L) software program. Mean pure tone audiometric thresholds in workers were significantly higher than in control subjects at frequencies 2,000, 4,000 and 6,000 Hz (p<0.05). Hearing losses were more evident at high frequencies (4-6 kHz) than at low frequencies in worker group. (p<0.05). It was observed that textile workers with longer employment duration had poorer hearing threshoulds and the hearing loss had started on those who had worked for 5-8 yr. While MDA levels were significantly higher in workers than controls (p<0.001), CAT activity was significantly lower (p<0.005). Also, SOD activity was lower in workers but difference was not statistically significant. We observed a significant change in hearing threshold of the textile workers compared with that of the control group. Increase in MDA level and decreases in CAT and SOD activities in textile workers, support the opinion that the noise causes the oxidative stress. The fact that noise both causes hearing loss and increases oxidative stress suggests that there may be a relationship between the oxidative stress and hearing loss. But, further studies are needed in order to verify this opinion.     

Individual Risk Factors in the Development of Noise-Induced Hearing Loss

We have analysed the association of noise-induced hearing loss with various risk factors among 685 workers in forest, shipyard, and paper mills. Occupational histories, health, environmental factors, and noise exposures of each worker were retrieved from the database of NoiseScan, our expert program on hearing. The mean hearing level at 4 kHz was 21.5 dB +/- 20.3 dB HL. It correlated significantly with age, noise emission level and noise exposure level. However, these factors could only explain about 2 dB HL of the variation in hearing level. Impulse noise in the shipyard work caused increase in hearing level of 12 dB HL at 4 kHz when compared to steady state noise exposure of forest work. Hearing level correlated with serum cholesterol levels, use of analgesics, blood pressure and smoking. An elevated cholesterol level increased hearing loss in both the high- and low-exposure groups. The use of analgesics did not increase a permanent threshold shift in the low-exposure group, but did in the high-exposure group. Systolic blood pressure, smoking, cholesterol level and the use of painkillers explained 36 % of the variation in hearing level at 4 kHz, whereas noise exposure alone explained 25 % of the corresponding variation.