The instrument used for data collection and analysis aimed to identify age range, gender and labor time, relate occupational/environmental sonorous exposure existence, in addition to characterizing difficulties in sound localization, speech perception, and the principal non-auditory signs and symptoms in workers with tinnitus as their principal complaint.
Other studies have been performed on similar populations [10, 12]. The first article, on the psychosocial effects of noise, evaluated 32 male workers exposed to noise, with 20 years mean labor time. Of these, 62.5% had acquired neurosensory hearing loss, and the principal complaint was tinnitus (68.7%). The second author evaluated 284 workers also exposed to noise, without distinguishing industrial or non-industrial exposure, and found prevalence rates of approximately 48% for tinnitus and 63% occupational exposure. The author concluded that there is not only an association between hearing loss and tinnitus, but also a dose–response relationship. The study sample was 70.7% male and 29.2% female, with 15.6 years mean labor time and mean age 42.5 years.
Authors  have reported a tinnitus prevalence rate of some 20% in workers with a history of occupational noise exposure. In our sample, however, the prevalence rate was 65.1%, far higher than reported elsewhere in the literature. This high percentage is probably related to the fact that the study focused on workers with hearing complaints and the demand reported by workers during the case work-up, the symptoms’ subjectivity, and the fact that no test was performed to assess the possibility of other influences (since it was not part of the objectives in the study design). This was also an experienced sample, with a mean age of 42.5 years and mean labor time of 15 years, despite the type of noise exposure.
In a Master’s thesis on the influence of noise spectrum on the prevalence of noise-induced hearing loss and tinnitus , 192 hearing tests were performed, preceded by an occupational case history. The author found a 45.8% rate of reported tinnitus, and the highest prevalence of tinnitus (56.4%) occurred in workers (49.0% of the sample) that presented audiometric results consistent with noise-induced hearing loss.
The symptom is the factor that leads to the most difficulties and scarcity of data in studies on tinnitus, along with some other problems such as: the fact that tinnitus is a symptom rather than a disease; the lack of objective measurement methods; lack of adequate experimental models; and variations in the individual’s emotional or physical status . The evaluation that can be used to record tinnitus is acuphenometry , but there is still no specific test for diagnosing tinnitus . However, speech therapy clinical practice relies on the patient’s perception of tinnitus, which is subjective and displays wide individual variability in self-reporting. This highlights the importance of the case history and physical and audiometric examination.
In our study, the analysis of hearing quality in workers with tinnitus showed that in occupational noise exposure, the prevalence of hearing loss was higher (79.6%) than that of normal hearing (20.4%). The same was true for tinnitus and environmental noise exposure, that is, a higher prevalence of hearing loss (69.2%) as compared to normal hearing (30.8%).
Similar results for hearing loss were detected in a retrospective study of 358 patients examined from January 1995 to June 1999 by the research group on tinnitus at the University of São Paulo (HCFMUSP)  in which clinical hearing loss was reported by 60.4% of patients.
A study on individuals with tinnitus and normal hearing  showed this is an important group to investigate, since the findings are not influenced by hearing loss. There are few studies in this field, and there are no longitudinal studies on the evolution of these patients. In a search for answers to these questions, 36 patients were selected from the same research group as in the previous study, from 1995 to 2003, who presented normal audiometry when they were included for follow-up. Although the study showed neither worsening of tinnitus over time nor significant changes in its characteristics, an important share of the sample evolved to hearing loss (7.4%).
In our study on workers with tinnitus, for both types of noise exposure (environmental and occupational), the majority of patients presented hearing loss; however, the proportion of patients with normal hearing was higher in cases of occupational noise exposure. This result is especially important when considering the findings that indicate evolution to hearing loss  and studies by other authors [5, 16] highlighting tinnitus as the first symptom of hearing dysfunction.
A literature review shows numerous articles in the occupational field describing the prevalence of hearing loss, for example a study in Greater Metropolitan Salvador, Bahia State, Brazil  in 7,925 workers from 44 factories in nine different branches of industry, showing 45.9% prevalence of hearing loss.
In marble workshops in Brasília, Federal District of Brazil, the prevalence of hearing injury was 48.0% . In the city of Goiania, a study in a metallurgical factory with 187 workers found a 22% prevalence of hearing loss, suggestive of noise exposure .
In São Paulo State, noise control programs in four metallurgical factories in the city of Piracicaba , with a total of 741 workers, were analyzed, showing 41% prevalence of hearing alterations, with workers’ mean age 42.3 years and 16.7 years mean labor time.
Another highly relevant question is the measurement of hearing function in relation to speech intelligibility in the audiological battery normally used in audiometric tests. In most routine examinations the battery is considered incomplete, since it does not include measures of speech recognition . Thus, in the attempt to understand these and other aspects, studies have been performed with the presence of competing noise and other factors.
One example  is a prospective clinical study in 60 adults, divided into 3 groups (20 with normal hearing, mean age 23.3 years; 20 with hearing loss, mean age 40.4 years; 20 elderly with hearing loss and mean age 66.8 years), aimed at investigating the effects of hearing loss and age on speech recognition in the presence of ipsilateral competing noise. The study showed a mean SRI proportion of 92% for all the groups studied, that is, no major difference was found between the three groups in terms of intelligibility performance, since the hearing thresholds at the speech frequencies were preserved. In our study, the mean SRI values in both the right and left ears were consistent with both the literature [19, 34] and the observed hearing conditions, not concerning the type of exposure. The values varied from 84.2% to 86.7% for hearing loss and from 93.5% to 98.1% for normal hearing, thus representing a limited number of failures in speech intelligibility. Even with values close to 88%, some speech recognition impairment is expected .
The observed hearing loss values reflect a small percentage-wise alteration in speech intelligibility, consistent with the literature [19, 34] and with the above-mentioned study , although the latter was not applied to individuals with tinnitus.
These minor alterations in speech recognition contrast with the high rates of difficulty in speech perception identified in normal hearing individuals complaining of tinnitus with occupational noise exposure (81.8%).
In 1986, Tyler & Baker  described the interrelationship between tinnitus and daily activities. In a public referral service for tinnitus, 49.3% of the 358 patients examined  reported impaired concentration in activities of daily living and 14.2% in social activities. In a previous study , the same service conducted a retrospective study of 150 patients in the Tinnitus Outpatient Clinic of the Department of Clinical Otorhinolaryngology at the FMUSP University Hospital and found that 76% reported some alteration in at least one activity of daily living, and that 47.3% reported difficulties in concentration. Our study found prevalence rates of 84.5% for sound localization difficulty (doorbell and telephone), 81.8% for speech perception (silent environment/presence of background noise), and 83.1% for otological signs and symptoms. These percentages in individuals with tinnitus with occupational noise exposure were similar to those found in environmental exposure. It is important to note that studies cited by Sanchez et al.  refer to a tinnitus specialist public ambulatory.
Since it is a cross-sectional study, the chronological relation between the events may not be easily detectable. It is about occupational/environmental noise exposed workers, having specific complaints like tinnitus, welcomed at a specific workers’ health Center. Age range shall not be considered as bias for hearing loss and tinnitus, since the age group includes hearing loss workers with ages below 30 years. Moreover, SRI evaluation methodology used corroborates for the findings.
As information bias, external factors as earplug use and vehicle, home and free-time noise may not be related.