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The literature relevant to risk factors will be discussed in this section.

3.5.1 Pupil age group

Preciado et al. (1998) [72] found an increased prevalence of self-reported voice problems in teachers of lower age groups with rates of 36% in nursery, 25% in

elementary and 21% in junior teachers. This may relate to the increased amount of oral instruction required in the teaching of younger children as it has been found that teachers speak at a higher level with younger pupils, possibly due to greater classroom noise and differences in classroom behaviour [35]. There are additional factors in terms of the voice levels and SF0 values of younger children relative to those of the

teachers (see section 2.2.1).

3.5.2 Subject taught

Teachers of certain subjects may be exposed to irritants in the classroom such as dust from metal and wood working, chemicals from painting, chlorine from swimming pools and the like. These agents can cause irritation to the voice system and may present an additional risk factor for voice problems.

Teachers of Physical Education have been shown to experience the highest rates of voice problems by subject taught [73, 74]. This may relate to working in acoustic environments poorly suited to speech, such as reverberant sports halls and swimming pools or in outdoor conditions with no natural speech reinforcement and the need to communicate over large distances.

In a study comparing teachers of different subjects, music and drama teachers did not report significant enhanced risks [73]. This may be due to higher levels of voice training and generally a greater awareness of voice use. Other reviews of the literature have noted an increased risk in teachers of singing and performing arts, along with sport and chemistry [71], therefore the evidence is not definitive.

3.5.3 Socio-economic factors

Classroom discipline may be influenced by socio-economic factors. In areas where children live in difficult circumstances it is perhaps unreasonable to expect children to arrive at school well fed, rested, relaxed and ready to learn. This may make children more disruptive and less receptive with associated voice and discipline challenges for

teachers. Discipline issues may increase stress levels for teachers with associated risks of voice problems (see section 3.5.7)

In some schools there may be a significant proportion of children within the pupil cohort who do not have English as their first language. This can place additional communication demands on teachers, as these children may find it more difficult to understand the teacher’s speech [75]. This may result in teachers having to repeat instructions or needing to talk louder due to more onerous speech intelligibility needs. This may also apply to children with attention disorders [76] or those with speech and language difficulties. Teacher demographics and associated risk factors will be discussed in the next section.

3.5.4 Teacher age

Teacher age has been found by Smith et al. (1998) [72] to be linked with voice problems. Ageing effects themselves are considered to only raise the risk of voice problems by a small amount; however the effect can be compounded by occupational voice use.

The physical effects of ageing relate to atrophy of the muscles and changes to the structure and lubrication of the vocal folds. These changes along with a reduction in respiratory capacity have the effect of reducing the frequency and dynamic ranges of the voice and altering the SF0.

Ageing affects the voices of men and women differently with changes at different times of life. The main ageing effects in men typically occur between 40 and 50 years of age. For women these effects are at the time of the menopause [55] when hormonal changes typically lead to a permanent increase in the mass of the vocal folds and a resultant lowering of SF0 [77]. The average age for the menopause in the UK is 51 [78].

3.5.5 Teacher gender

There is research to show that women, irrespective of occupation, have a higher frequency of voice disorders compared to men. As the majority of school teachers are

women this may contribute to the apparent high prevalence of voice problems in teachers overall.

Smith et al. (1998) [38] found that, almost without exception, the full range of adverse vocal symptoms were reported at a significantly higher rate in female respondents compared with male respondents, and that the gender factor was more significant for the teaching rather than the non-teaching group.

Over 38% of female respondents reported that teaching had had an adverse impact on their voices (33% for men), and female respondents were more likely to seek medical attention for voice problems (19% versus 8%) [38]. However this difference in seeking medical attention has also been found to apply to the general population [79] and may not indicate a greater prevalence in itself.

Another study by Smith et al. in 1998 [72] investigated whether there was a greater prevalence of voice problems taking account of occupation and work activities along with gender. Female teachers consistently reported a greater prevalence of voice problems, with 38% of female teachers reporting both acute and chronic voice problems compared to 26% of their male colleagues. This was irrespective of the subject taught or number of years of teaching. Other studies have found similar patterns [59, 60].

Phoniatric examinations were undertaken in a study by Lejska (1967) [63] as mentioned previously. The study found higher levels of voice pathology in female teachers. Other studies have found similar results [64, 65].

There are a number of physiological factors which may contribute. Women typically have lower hyaluronic acid levels, a material important in the repair and resilience of the vocal folds [80].

Pregnancy and the menstrual cycle can both have short term effects on the voice, where variations in oestrogen levels can cause increased mass of the vocal folds leading to a reduced SF0 and decreased upper range [77]. As previously noted in

section 3.5.4 significant changes occur to the vocal fold tissues in women of menopausal age and this may lead to particular vulnerabilities for female teachers

[55]. It has also been suggested that women may be at greater risk of developing voice disorders due to different coping strategies for stress, depression and anxiety [81].

3.5.6 Stress

Stress is a significant contributory factor to ill health in general and also to occupational health and voice problems. Stress can be defined as an interaction between environmental demands and an individual’s ability to respond to those demands.

Stress is, in statistical terms, one of the biggest workplace health problems across all occupations. In the UK stress accounted for 35% of all work related ill health cases and 43% of all working days lost due to ill health in 2014-2015 [82].

Teachers have relatively high rates of work related stress, anxiety and depression according to official estimates, the rate being second only to health professionals, with teachers having an estimated rate of 2190 cases per 100,000 people employed (almost twice that of the general population). Around half of all ill health retirements in teachers are due to stress and/or psychiatric illnesses, with the other half for physical illnesses or disabilities [83]. The high prevalence of stress in teachers implies a systemic mismatch between the requirements of the profession and the abilities of teachers to meet these demands.

Education as a sector is subject to a high degree of political intervention with a heavy burden of administration and bureaucracy. There are frequent changes to curricula, assessment techniques and performance criteria as well as the pressures associated with league tables and Ofsted inspections which are likely to create intrinsic stress for teachers. This is coupled with the demands of teaching itself, particularly against a backdrop of low teacher morale, discipline problems, large class sizes and limited resources.

There has also been the integration of children with special educational needs into mainstream schooling which may place an additional responsibility on teachers. These occupational factors are in addition to the general stresses applicable to all in the

modern world and the interaction between personal and workplace stress must also be considered in terms of the stress capacity of individuals.

Stress can have a number of effects on the voice which are discussed further in the next section.

3.5.7 Voice related effects of stress

Research by Green (1989) [84] indicated a relationship between stress and voice problems. A number of stress responses can influence voice production directly:

• Neck, shoulder and back tension affect the movement of the larynx and rib cage.

• Dry mouth.

• Fast and shallow breathing which can affect phonation efficiency.

Other changes can influence the voice system indirectly:

• Stress hormones released as part of the physiological response.

• Frequent urination and diarrhoea can cause dehydration increasing the potential for vocal damage.

• Suppressed immune system increasing vulnerability to respiratory tract infections.

• Indigestion and acid reflux irritating the voice system.

• Interference with swallowing which may encourage throat clearing or coughing.