Tinnitus is a common experience with up to one third of the adult population experiencing it at some time in their life. Less than 1% of the adult population have tinnitus of sufficient severity to affect their quality of life seriously (although up to 8% may seek medical advice about it). Much of the severity of tinnitus relates to the individuals' psychological response to the abnormal tinnitus signal. The prevalence of tinnitus increases in association with high frequency hearing loss. There is, unfortunately, no diagnostic test that either confirms the presence of tinnitus or its severity. Currently there is no satisfactory severity grading system. A five-point severity grading scheme is therefore proposed and the entry criteria detailed. The five severity points are: slight, mild, moderate, severe and catastrophic. Categorization as 'severe' or 'catastrophic' should be, by epidemiological definition, very rare. General guidance, theory and evidential support are contained within.

These guidelines aim to assist in the diagnosis of noise-induced hearing loss (NIHL) in medicolegal settings. The task is to distinguish between possibility and probability, the legal criterion being 'more probable than not'. It is argued that the amount of NIHL needed to qualify for that diagnosis is that which is reliably measurable and identifiable on the audiogram. The three main requirements for the diagnosis of NIHL are defined: R1, high-frequency hearing impairment; R2, potentially hazardous amount of noise exposure; R3, identifiable high-frequency audiometric notch or bulge. Four modifying factors also need consideration: MF1, the clinical picture; MF2, compatibility with age and noise exposure; MF3, Robinson's criteria for other causation; MF4, complications such as asymmetry, mixed disorder and conductive hearing impairment.

To allocate sufficient resources to clinical services or to research and development in the most effective way possible, statistics are needed on the prevalence of the condition in question for various degrees of severity. For the United Kingdom, such data for tinnitus have become available from two recent large-scale studies. The first is the National Study of Hearing (NSH) which is being conducted by the Medical Research Council's Institute of Hearing Research from its headquarters in Nottingham and its clinical outstations in Cardiff, Glasgow, Nottingham and Southampton. It started in 1978 and is now entering its third phase. The second study is the General Household Survey carried out in 1981 by the UK Office of Population Censuses and Surveys (OPCS). The rationale and methodology of the NSH and the prevalence data obtained up to the present, together with those from the OPCS survey, will be given in this paper; the demographic data and the clinical aspects of the study will be presented in the accompanying paper (IHR, 1984).

This report describes a three-centre study of the effectiveness of tinnitus maskers, combination instruments (masker plus hearing aid), and hearing aids in the management of tinnitus. Some 472 patients entered the study with 382 reaching the first evaluation session after a minimum period of 6 months from fitting, and 206 reaching the second evaluation not less than 6 months after the first. The study included two control groups, by which to assess the comparative benefit to be derived solely from the investigation and counselling of such patients. The principal results were as follows: thorough investigation and careful counselling do much to help the patient; much further benefit is given by tinnitus masking instruments of various kinds; maskers are more often effective than hearing aids, although the latter are frequently the most appropriate first treatment of those patients who have substantial (but not yet treated or insufficiently treated) hearing difficulties as well; there is no evidence of masking having any harmful effect on hearing. None of the audiometric or tinnitus tests currently employed can be regarded as predictive, either of tinnitus severity, or of the eventual outcome of masking therapy, however certain measurements may help as a guide to patient management.

A self-administered questionnaire concerning auditory disability and handicap was completed by 1691 subjects who were part of a two-stage random sample of the UK adult population. A principal components analysis of questionnaire replies identified four components. They were interpreted as (a) disability for everyday speech, (b) disability for speech-in-quiet, (c) localisation, and (d) hearing handicap. Components (a) and (d) were the strongest, accounting for 68% of the variance. Subjects also performed pure-tone audiometry amongst other tests. Audiometric information was well described by a two-parameter model characterised by low-to-mid-frequency loss and high-frequency slope. All four components increased progressively with increasing low-to-mid-frequency loss, independent of high-frequency slope. They were best correlated with a binaural average over 0.5, 1 and 2 kHz weighted 4:1 in favour of the better ear, out of several audiometric descriptors examined. Sex and socio-economic group did not generally affect disability or handicap, but people of similar hearing impairment reported less disability and handicap as age increased. This is interpreted as over-compensation for the effects of age in self-report. There were three unexpected findings which may entail some changes in current thinking on the relationship between auditory impairment and self-perceived disability/handicap. Hearing losses incorporating a conductive component in the better ear were more disabling and handicapping than sensorineural losses of equal magnitude. Localisation ability and, to a lesser extent, general hearing handicap were more highly correlated with measures of impairment in the worse ear than in the better ear. There was little evidence for the concept of a 'low fence' in the relationship between impairment and either disability or handicap.