Parental involvement in school work has been shown to have beneficial effects on child performance (M asselam et al., 1990; Steinberg et al., 1992). Given that most o f these children live in high aircraft noise exposed homes it is reasonable to assume that aircraft noise interferes with daily activities and communication in the home (Job, 1988), such that parents may be less likely to help at home with homework. Michelson (1968) found that a good study environment at home (quiet secluded place to study) buffers the effect of school noise exposure on children’s reading ability. As noise may have independent
effects on child performance and on the likelihood of parental assistance with school work, it is possible that parental help at home may influence the association between aircraft noise exposure and cognitive performance in children.
4.1.8 Specific hypotheses It is hypothesised that:
(1) Chronic aircraft noise exposure produces cognitive impairments in reading comprehension. (Between subjects analysis)
(2) Chronic aircraft noise exposure produces a delay in the progress o f reading comprehension over the period of a year. (Within subjects analysis)
(3) Sustained attention mediates the noise effects on reading comprehension. (Between subjects analysis)
(4) Chronic aircraft noise exposure produces cognitive impairments in sustained attention. (Between subjects analysis)
(5) Chronic aircraft noise exposure in school children is associated with higher levels o f noise annoyance. (Between subjects analysis)
(6) The baseline psychological mediating results are replicated. Specifically:
6.1 That depression, anxiety, self-reported stress and noise annoyance do not mediate the relationship between chronic aircraft noise exposure and cognitive performance. 6.2 That depression, anxiety and self-reported stress do not mediate the relationship between chronic aircraft noise exposure and annoyance.
The follow in g hypotheses are exploratory and are not based on strong predictions from previous research. It is hypothesised that:
(7) Chronic aircraft noise exposure in school children will be associated with higher levels of self-reported stress than in children in schools exposed to lower levels of aircraft noise. (Between subjects analysis)
(8) Parental interest in school work influences the effect of noise on cognitive performance. (Between subjects analysis)
4.2 Results
The results will be divided into 5 sections. Section 1 contains the background description of the sample and noise exposure levels. Section 2 contains the cross sectional/between subjects results of the main noise effects in children. Section 3 contains the results of the within subjects analyses of noise effects in children over the period of a year. Section 4 contains the analyses to test the mediating factors that m ay influence the main noise effects in children. Section 5 contains a summary of the psychometric analyses.
4.2.1 Section I - Descriptive results
4.2.1.1 Response rate
The overall child response rate was 81% (n=275) of the baseline sample across the eight schools; 10 % (n=35) of the original 340 sample declined to take part in 1997; 6% (n=19) o f the original sample had moved; 3% (n= 11) of the original sample were away at the time of testing. The socio-demographic characteristics of the declining sample and the sample that had moved were not significantly different to the participating sample in terms of sex, race, age and social class.
4.2.1.2 Socio-demographic characteristics of the sample
As before at baseline, the sample was well matched across noise levels for: class at school, sex, proportion of socio-economic groups, social class and level o f deprivation (see Table 18 below). The sample was less well matched on main language spoken at home and race (see Table 18 below). The high noise school sample had a higher proportion o f non-white and non-English as the main language spoken at home than the low noise schools. Chi-squared tests (%2) were run to assess total differences between
high and low noise exposed samples (see Table 18 below, data taken from the 1996 parent questionnaire).
T able 18.
The socio-demographic characteristics o f the high and low noise child samples in 1997: frequencies and proportions. (Follow-up Study)
Socio-D em ographic C h aracteristic H igh Noise N=148 Low Noise N=127 Year 5 Year 6 66 (45%) 82 (55%) 55 (43%) 72 (57%) Girls Boys 74 (50%) 74 (50%) 69 (54%) 58 (46%) White Non-White 49 (36%) 86 (64%) 111 (89%) 14 (11% )*
English - Main Language Spoken at Home Non-English
90 (66%) 46 (34%)
116 (94%) 8 (6%) *
Non-Manual Social Class (1,2,3N) Manual Social Class (3M,4,5)
42 (47%) 48 (53%)
49 (58%) 36 (42%)
Professional Groups SEGs (1,2,3,4) Other non-manual workers SEGs(5,6) Skilled Manual Workers SEGs (8,9,12) Semi-Skilled Manual W orker SEGs(7 &10) Unskilled S E G (ll) Others SEGs (13,14,15,16,17) 19 (21%) 24 (26%) 24 (26%) 12 (14%) 11 (12%) 1 (1%) 22 (25%) 30 (35%) 25 (29%) 8 (9%) 1 (1%) 1 (1%) Not Deprived Deprived 68 (53%) 60 (47%) 70 (63%) 41 (37%)
Note. Total percentages reported are of those known. Missing data are generally a small proportion of the sample, except in the case of social class, socio-economic group and deprivation.
* Chi-squared tests were only run on total rows, these items (y l) p<0.05. 4.2.1.3 Noise exposure
Chronic Aircraft Noise Exposure A t School
There is no reason to assume that the chronic levels of aircraft noise changed in the eight schools as there was no significant change in flight frequency at Heathrow Airport over the period of a year (Turner, 1997). See Table 8 in Chapter 3 for chronic aircraft noise levels at the 8 schools.
Home Aircraft Noise Exposure
Noise exposure at home was strongly associated with noise exposure at school
according to local noise contours (1991 CAA noise contours). 80% of the children in high noise exposed schools lived in high noise exposed homes (>63 dBA Leq 16hr) and
87 % of the children in low noise schools lived in low noise homes (<57 dBA Leq 16hr) (see Table 19 Below).
Table 19.
Proportion o f high and low school noise samples in high, moderate and low aircraft noise exposed homes taken from the 1994 CAA noise contour maps f o r the 1997 sample. (Follow-up Study)