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Critique of subjective responses of Chinese to aircraft noise
Applied Acoustics 17 (1984) 223 232
Critique of Subjective Responses of Chinese to Aircraft Noise A. L. B r o w n * Environmental Protection Agency, Empire Centre, Tsim Sha Tsiu, Kowloon (Hong Kong) (Received: 24 August, 1982)
SUMMARY A recent paper 1 has reported a difference in response to aircraft noise between the community living around Hong Kong International Airport and that living around Heathrow Airport in the UK. The difference has been ascribed to a different sensitivity of" Chinese in Hong Kong to aircraJt noise. This paper questions whether any such difference exists and suggests that the result is more likely a function of the techniques o f survey and analysis adopted in the Hong Kong study. This is" based on a statistical comparison of the regression lines and on an examination o f the problems associated with transferring an annoyance scale developed in one environment to another.
INTRODUCTION A recent paper by K o and Lei 1 claims to provide evidence o f a cultural difference between Chinese and E u r o p e a n s in sensitivity to aircraft noise. The a u t h o r s c o m p a r e d results f r o m the first (1961) H e a t h r o w Survey o f aircraft noise a n n o y a n c e 2 with those o f a similar survey they c o n d u c t e d * Present address: School of Australian Environmental Studies, Griffith University, Nathan 4111 (Australia), 223 Applied Acoustics 0003-682X/84/$03.00 ~ Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
224
A, L. Brown
--
I
1
|
I
3
Z
2
0
I
I
I
40
58
60
NOISE AND
"/0
NUMBER INDEX
Fig. 1. Comparison of the dose-response relationships for grouped data from the 1961 Heathrow study (. . . . . ) and the Hong Kong study ( -), reproduced from reference 1.
under the flight-path of Hong Kong International Airport. They reported, 'the present observation suggests that the Chinese of Hong Kong are less sensitive (to aircraft noise) than Europeans'. This finding was based primarily on their plot, reproduced here as Fig. l, of dose-response relationships from the two studies. Given the traditional view of a divergence between eastern and western cultures, certainly in such matters as family, social interaction and, perhaps, perception of environment, this postulate of a different cultural response to aircraft noise cannot be discounted out of hand. Another explanation--not suggested by the authors--is that, rather than being culturally based, the difference could be the outcome of the remarkably different living conditions enjoyed by the respective study populations. Broadly, the Heathrow population lived in two-storey houses with residential densities throughout the study area ranging from 500 up to some 6000 persons per square kilometre. 3 By contrast, the Hong Kong population was housed in high-rise buildings of up to 15 storeys with residential densities of up to 200000 persons per square kilometre. 4 This comparison provides at least a coarse indicator of disparate living environments. Under such disparate conditions, noise may, for the time being, rank differently on any hierarchy of
Critique of subjective responses of" Chinese to aircraft noise
225
environmental concerns held by the respective populations, and response to noise, as measured by a social survey, might reasonably be expected to be different. However, on closer inspection of the evidence presented, one need turn to neither of these hypotheses to explain the reported difference in response in the two surveys. It is argued below that the difference may be more apparent that real, a function of the techniques of survey and analysis adopted in the Hong Kong study. There are at least three grounds for major concern and these are discussed below.
C O M P A R I S O N OF THE REGRESSION LINES The first ground for concern is whether the two regression lines in Fig. 1 can confidently be said to be different from each other or whether the difference could have arisen merely by chance. The authors did not address this question, nor did they provide sufficient data to allow statistical testing of the differences between the slopes and between the intercepts of the two lines. A statistically significant difference in either or both is required. 5 However, despite the lack of data, it is still possible to estimate confidence limits for the respective regression lines and the extent of overlap of these limits gives some guidance on the likelihood that the difference between lines may have arisen only by chance. The group response data to which the Heathrow line of Fig. 1 was the best fit have been published (Table II, p. 207 of reference 2), and from this data the correlation coefficient can be calculated (r = 0-99). The sample size was 8, and the standard deviation of group annoyance scores (St) was 0.78. Based on these statistics, 95 per cent confidence limits for this regression line can be calculated 6 and are shown in Fig. 2. The narrow confidence limits for the Heathrow data reflect the fact that this sample was the one used to develop the original NNI equation; the combination of the two independent physical variables (Noise Level and Number of Flights) being manipulated to maximize the correlation between them (as NNI) and community response. Because this manipulation has enhanced the correlation of NNI and response, the confidence limits shown can be regarded as exceptionally conservative (narrow) in the present context of examining any overlap with the limits of another regression line. For the Hong Kong data the only published statistic of the regression is the correlation coefficient, (r = 0.45, Table I of reference 1). The equation
A. L. Brown
226 6
I
I
I
4t-
z 2
0 L~::,:,,,:....
I
I
I
20
30
40
NOISE AND
50
60
70
NUMBER INDEX
Dose response regression lines for grouped data. The shaded areas show the 95 per cent confidence limits for each regression line. (. . . . . ,1961 Heathrow study; - Hong K o n g study; -, 1967 Heathrow study). Fig.
2.
of the regression line can be estimated by scaling from Fig. 1 (Y= - 2 . 3 4 + 0 - 0 9 7 X ) . The sample size has not been reported, but it presumably was no larger than 11 (based on respondents grouped into 3 N N I intervals over the range 35 to 70 N N I shown in Fig. 4 of reference 1). From these statistics the standard deviation in group response (Sy) for the Hong Kong study can be calculated* (2.05) and 95 per cent confidence limits for the regression line estimated. These confidence limits are also drawn in Fig. 2. Note that in this Figure the regression lines have been shown only over the ranges of the original data of the respective studies. Figure 2 shows that the confidence limits for the regression lines from the Hong Kong study and the 1961 Heathrow study clearly overlap. In contrast to the 'obvious' difference observed from Fig. 1, Fig. 2 suggests that the authors' statement regarding different dose-response relationships in London and Hong Kong (or, by their extrapolation, between European and Chinese) should, at the very least, have been more cautious. * The slope of the regression line (B~x), the correlation coefficient (r) and the standard deviations of X and Y (S x and St) are related in the following manner: 7
By~ = rSv/Sx
Critique of subjective responses of Chinese to aircraft noise
227
This is further reinforced by superpositioning on Fig. 2 the dose-response relationship obtained in the second survey (1967) of aircraft noise annoyance around Heathrow (regression line and 95 per cent confidence limits calculated from data in Table P3 of reference 8). Because of the overlap in limits one can reasonably reject claims that the dose-response relationships in the two Heathrow studies are different and that the dose-response relationships obtained in the 1967 Heathrow survey and the Hong Kong survey are different.
PROBLEMS WITH THE A N N O Y A N C E SCALE The second ground for concern is that the results of the Hong Kong survey could have been biased by the authors' apparently uncritical application of the annoyance scale developed by Guttman scaling techniques in the 1961 Heathrow survey. 9 Essentially, this scale is based on annoyance caused by disturbance to various activities and to understand the possible source of bias it is necessary to be familiar with the complex scoring procedure (see Table 1). The potential problem in applying such a scale in an environment other than that in which it was developed (apart from ensuring comparability of response in a different language and in a different culture--unfortunately not addressed by the authors) is best explained by a simple example. Suppose a hypothetical population was affected by noise to an extent similar to that of the Heathrow population and also that they were also as bothered by noise and reported as much annoyance with activities. But assume, further, that this population did not possess television or radio. These respondents could not experience television/radio interference, could not report that it caused annoyance and could not score on this activity interference in Table 1. Respondents from this hypothetical group could, simply as a figment of scale construction, score a maximum of 5, rather than 6, on the annoyance scale, and the group as a whole would have annoyance scores somewhat lower than their Heathrow counterparts. While there is no shortage of radio or television sets in Hong Kong, Table 2, taken from the authors' paper, raises similar concerns with respect to other activities. The Table shows that there was less frequent reporting of annoyance with all activity interferences in Hong Kong, with the exception of speech interference. This could mean one of two things. It
TABLE 1
X
--
A little
Not at all
No
Adapted from Appendix L of reference 8.
Wake you up Interfere with conversation Interfere with TV/radio House vibrates Startle you Other activities Other effects
Activity interference Moderately X X X X X X X
X X X X X X X
Yes
any one
Very
ITEM C. 'When they (each interference) how annoyed does this make you feel?'
ITEM B. "Do aircraft ever (interference listed below)?' If yes, ask C.
X - X
Very much Moderately
ITEM A. 'Tell me how much the noise of the aircraft bothers or annoys you?'
any one
) +1
SUM R I G H T - H A N D C O L U M N TO OBTAIN ANNOYANCE SCORE (Range of 0 to 6)
w
--]
+1
~- +1 m
X X X X X
(ITEM C) +1 +1
Not at all
(ITEM B)
~+1
--
A little
Construction of The Annoyance Scale (Responses Corresponding To X Score + 1 As Indicated) Oo
t~
Critique of subjective responses o[ Chinese to aircraft noise
229
TABLE 2
Percentage of Respondents Very Annoyed or ModeratelyAnnoyed by Interferenceof Aircraft Noise with Various Activities Hong Kong Speech interference Listening to radio/TV House vibrates Other interference Wake up Startle
28 21 7 7 11 9
Heathrow 1961
1967
20 25 18 6 25 25
24 32 19 12 19 13
From reference 1. could mean that the Hong Kong population might not be annoyed by having their activities interfered with--part of their lower sensitivity to noise, as claimed by the authors. But it could equally mean that many of the Hong Kong respondents did not experience these interferences. For example, Hong Kong respondents, nearly all of whom were on the ground floor level of multi-storey concrete buildings, may not have experienced the "house vibrating' in the way their Heathrow counterparts, living in detached, semi-detached or row housing, might have. Further, some proportion of respondents were interviewed in commercial premises (personal communication from the authors, I OA Meeting (HK Branch), March, 1963). (Much of the study area has a mixed land use with ground floor levels of the high-rise residential buildings used for commercial purposes.) These respondents worked in the commercial premises but would not necessarily have resided in that building, and those of them who lived outside the study area presumably would not have reported being awoken by aircraft noise. In commercial premises one might also expect that activities associated with commercial pursuits may dominate over the essentially domestic activities included in the annoyance scale. Respondents who could not experience specific activity interferences could not, of course, report annoyance with such interferences and so contribute towards their Annoyance Score. While all this is conjectural, without information on the comparative frequency o f activity interferences in the Hong Kong and Heathrow populations, as distinct from the frequency o f annoyance with activity interferences reported in Table 2, the possibility remains that the application of this particular type
230
A. L. B r o w n
of annoyance scale in the different physical environment of Hong Kong may have resulted in a downward bias in Annoyance Scores, vis-a-vis the Heathrow scores, quite unrelated to any difference in sensitivity to noise.
ATTITUDE TO QUESTIONNAIRES Thirdly, there are two results from the Hong Kong social survey which raise further questions about the comparability of the Hong Kong and Heathrow results--not in terms of a cultural difference in sensitivity to noise, but perhaps one of a cultural difference in response to questionnaires. In the questionnaire, opportunity was provided for respondents to spontaneously mention hearing aircraft noise. This was followed by a specific prompt as to whether respondents ever heard aircraft. There remained, after the second question, 23.3 per cent of the Hong Kong sample who never heard aircraft; a remarkable result given that the lowest aircraft noise exposure experienced was about 40 NNI. The equivalent figures in the 1961 and 1967 Heathrow studies were 3 per cent and 6 per cent, respectively, but at Heathrow the population included respondents with an exposure as low as 15 NNI. If almost a quarter of the Hong Kong sample did not hear aircraft despite very direct questioning, why not? Is the physical environment in Hong Kong sufficiently different, particularly at the ground floor level, that many respondents could not hear aircraft? If so, this would lend credence to the above argument regarding frequency of activity interference. Or could respondents, for their own purposes, have opted for the most neutral response, 'no'? This is discussed further below. In any case, a finding that a quarter of respondents in a dose-response study for aircraft noise did not 'hear' the dose should have been a cause for alarm to a researcher (was the dose measured adequately?) and certainly have prompted caution in comparing results with those of another study. Respondents were also asked another question: 'On the whole, would you say that you were more bothered by aircraft in the past, or have you got used to them?' The responses are not of interest here, except for the 28 per cent of respondents who did not offer an opinion, preferring to report ~don't know'. In the Heathrow surveys, the equivalent 'don't know' responses were only 4 per cent (1961 survey) and 1 per cent (1967 survey). The authors of the Hong Kong study comment: 'The high percentage of
Critique of subjective responses of Chinese to aircraft noise
231
"don't knows" implies the non-committal characteristics of the Chinese in Hong Kong'. They do not, however, draw the logical conclusion that if their respondents had been non-committal in one part of the questionnaire, they are quite likely to have been similarly inclined in others, including the component questions of the annoyance scale. Before a respondent could score on any of the activity interferences of Item C of Table 1, he had to be sufficiently willing to answer affirmatively to Item B. A low Annoyance Score resulting from a respondent's cultural propensity to being non-committal in a survey interview is something very different from a low Annoyance Score resulting from insensitivity to noise. It suggests that the social survey instrument, developed for the population around Heathrow airport, may not have been a suitable instrument for measuring the true effect of noise on the Chinese community living near the Hong Kong airport. CONCLUSION In conclusion, the authors are to be commended for attempting a comparative analysis of response across two different airports and two different cultures. The study of dose-response relationships for transportation noise sources has certainly been hampered by the multiplicity of measurement instruments, both for dose and for response, adopted by different researchers. However, it is unfortunate that this attempt has not been tempered by an understanding of the pitfalls of imposing a social survey instrument developed in one environment on another, and on the necessity for rigour when drawing conclusions on the differences between populations based on sample data. One needs to be particularly careful where premature conclusions about a population's sensitivity, or, in this case, insensitivity, to noise could become encoded in legislative and planning control which may relegate that population to high levels of noise exposure into the foreseeable future. REFERENCES 1. N. W. M. Ko and P. C. K. Lei, Subjective responses of Chinese to aircraft noise. Applied Acoustics, 15 (1982), pp.251 61. 2. Anon., Command2056 Noise: Final Report of the Committee on the Problem of Noise, HMSO, 1963.
232
A. L. Brown
3, E~ Jones and D. J. Sinclair, Atlas oJ London and the London Region, Pergamon, Oxford, 1968. 4. Hong Kong, Population Map 1:350,000. Series AR/2/P, 1978. 5. J. Neter and W. Wasserman, Applied linear statistical models, Richard Irwin, 1974. 6. R. E. Walpole and R. H. Myers, Probability and statisticsjor engineers and scientists, Collier MacMillan, 1972. 7. J. Cohen and P. Cohen, Applied multiple regression/correlation analysisjor the behavioral sciences, Lawrence Erlbaum Associates, 1975. 8. Anon., Second survey of aircraft noise annoyance around London (Heathrow) Airport, HMSO, 1971. 9. A. C. McKennell, Aircraft noise annoyance around London (Heathrow) Airport, Central Office of Information, SS Report 337, HMSO, 1963.
Critique of Subjective Responses of Chinese to Aircraft Noise A. L. B r o w n * Environmental Protection Agency, Empire Centre, Tsim Sha Tsiu, Kowloon (Hong Kong) (Received: 24 August, 1982)
SUMMARY A recent paper 1 has reported a difference in response to aircraft noise between the community living around Hong Kong International Airport and that living around Heathrow Airport in the UK. The difference has been ascribed to a different sensitivity of" Chinese in Hong Kong to aircraJt noise. This paper questions whether any such difference exists and suggests that the result is more likely a function of the techniques o f survey and analysis adopted in the Hong Kong study. This is" based on a statistical comparison of the regression lines and on an examination o f the problems associated with transferring an annoyance scale developed in one environment to another.
INTRODUCTION A recent paper by K o and Lei 1 claims to provide evidence o f a cultural difference between Chinese and E u r o p e a n s in sensitivity to aircraft noise. The a u t h o r s c o m p a r e d results f r o m the first (1961) H e a t h r o w Survey o f aircraft noise a n n o y a n c e 2 with those o f a similar survey they c o n d u c t e d * Present address: School of Australian Environmental Studies, Griffith University, Nathan 4111 (Australia), 223 Applied Acoustics 0003-682X/84/$03.00 ~ Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
224
A, L. Brown
--
I
1
|
I
3
Z
2
0
I
I
I
40
58
60
NOISE AND
"/0
NUMBER INDEX
Fig. 1. Comparison of the dose-response relationships for grouped data from the 1961 Heathrow study (. . . . . ) and the Hong Kong study ( -), reproduced from reference 1.
under the flight-path of Hong Kong International Airport. They reported, 'the present observation suggests that the Chinese of Hong Kong are less sensitive (to aircraft noise) than Europeans'. This finding was based primarily on their plot, reproduced here as Fig. l, of dose-response relationships from the two studies. Given the traditional view of a divergence between eastern and western cultures, certainly in such matters as family, social interaction and, perhaps, perception of environment, this postulate of a different cultural response to aircraft noise cannot be discounted out of hand. Another explanation--not suggested by the authors--is that, rather than being culturally based, the difference could be the outcome of the remarkably different living conditions enjoyed by the respective study populations. Broadly, the Heathrow population lived in two-storey houses with residential densities throughout the study area ranging from 500 up to some 6000 persons per square kilometre. 3 By contrast, the Hong Kong population was housed in high-rise buildings of up to 15 storeys with residential densities of up to 200000 persons per square kilometre. 4 This comparison provides at least a coarse indicator of disparate living environments. Under such disparate conditions, noise may, for the time being, rank differently on any hierarchy of
Critique of subjective responses of" Chinese to aircraft noise
225
environmental concerns held by the respective populations, and response to noise, as measured by a social survey, might reasonably be expected to be different. However, on closer inspection of the evidence presented, one need turn to neither of these hypotheses to explain the reported difference in response in the two surveys. It is argued below that the difference may be more apparent that real, a function of the techniques of survey and analysis adopted in the Hong Kong study. There are at least three grounds for major concern and these are discussed below.
C O M P A R I S O N OF THE REGRESSION LINES The first ground for concern is whether the two regression lines in Fig. 1 can confidently be said to be different from each other or whether the difference could have arisen merely by chance. The authors did not address this question, nor did they provide sufficient data to allow statistical testing of the differences between the slopes and between the intercepts of the two lines. A statistically significant difference in either or both is required. 5 However, despite the lack of data, it is still possible to estimate confidence limits for the respective regression lines and the extent of overlap of these limits gives some guidance on the likelihood that the difference between lines may have arisen only by chance. The group response data to which the Heathrow line of Fig. 1 was the best fit have been published (Table II, p. 207 of reference 2), and from this data the correlation coefficient can be calculated (r = 0-99). The sample size was 8, and the standard deviation of group annoyance scores (St) was 0.78. Based on these statistics, 95 per cent confidence limits for this regression line can be calculated 6 and are shown in Fig. 2. The narrow confidence limits for the Heathrow data reflect the fact that this sample was the one used to develop the original NNI equation; the combination of the two independent physical variables (Noise Level and Number of Flights) being manipulated to maximize the correlation between them (as NNI) and community response. Because this manipulation has enhanced the correlation of NNI and response, the confidence limits shown can be regarded as exceptionally conservative (narrow) in the present context of examining any overlap with the limits of another regression line. For the Hong Kong data the only published statistic of the regression is the correlation coefficient, (r = 0.45, Table I of reference 1). The equation
A. L. Brown
226 6
I
I
I
4t-
z 2
0 L~::,:,,,:....
I
I
I
20
30
40
NOISE AND
50
60
70
NUMBER INDEX
Dose response regression lines for grouped data. The shaded areas show the 95 per cent confidence limits for each regression line. (. . . . . ,1961 Heathrow study; - Hong K o n g study; -, 1967 Heathrow study). Fig.
2.
of the regression line can be estimated by scaling from Fig. 1 (Y= - 2 . 3 4 + 0 - 0 9 7 X ) . The sample size has not been reported, but it presumably was no larger than 11 (based on respondents grouped into 3 N N I intervals over the range 35 to 70 N N I shown in Fig. 4 of reference 1). From these statistics the standard deviation in group response (Sy) for the Hong Kong study can be calculated* (2.05) and 95 per cent confidence limits for the regression line estimated. These confidence limits are also drawn in Fig. 2. Note that in this Figure the regression lines have been shown only over the ranges of the original data of the respective studies. Figure 2 shows that the confidence limits for the regression lines from the Hong Kong study and the 1961 Heathrow study clearly overlap. In contrast to the 'obvious' difference observed from Fig. 1, Fig. 2 suggests that the authors' statement regarding different dose-response relationships in London and Hong Kong (or, by their extrapolation, between European and Chinese) should, at the very least, have been more cautious. * The slope of the regression line (B~x), the correlation coefficient (r) and the standard deviations of X and Y (S x and St) are related in the following manner: 7
By~ = rSv/Sx
Critique of subjective responses of Chinese to aircraft noise
227
This is further reinforced by superpositioning on Fig. 2 the dose-response relationship obtained in the second survey (1967) of aircraft noise annoyance around Heathrow (regression line and 95 per cent confidence limits calculated from data in Table P3 of reference 8). Because of the overlap in limits one can reasonably reject claims that the dose-response relationships in the two Heathrow studies are different and that the dose-response relationships obtained in the 1967 Heathrow survey and the Hong Kong survey are different.
PROBLEMS WITH THE A N N O Y A N C E SCALE The second ground for concern is that the results of the Hong Kong survey could have been biased by the authors' apparently uncritical application of the annoyance scale developed by Guttman scaling techniques in the 1961 Heathrow survey. 9 Essentially, this scale is based on annoyance caused by disturbance to various activities and to understand the possible source of bias it is necessary to be familiar with the complex scoring procedure (see Table 1). The potential problem in applying such a scale in an environment other than that in which it was developed (apart from ensuring comparability of response in a different language and in a different culture--unfortunately not addressed by the authors) is best explained by a simple example. Suppose a hypothetical population was affected by noise to an extent similar to that of the Heathrow population and also that they were also as bothered by noise and reported as much annoyance with activities. But assume, further, that this population did not possess television or radio. These respondents could not experience television/radio interference, could not report that it caused annoyance and could not score on this activity interference in Table 1. Respondents from this hypothetical group could, simply as a figment of scale construction, score a maximum of 5, rather than 6, on the annoyance scale, and the group as a whole would have annoyance scores somewhat lower than their Heathrow counterparts. While there is no shortage of radio or television sets in Hong Kong, Table 2, taken from the authors' paper, raises similar concerns with respect to other activities. The Table shows that there was less frequent reporting of annoyance with all activity interferences in Hong Kong, with the exception of speech interference. This could mean one of two things. It
TABLE 1
X
--
A little
Not at all
No
Adapted from Appendix L of reference 8.
Wake you up Interfere with conversation Interfere with TV/radio House vibrates Startle you Other activities Other effects
Activity interference Moderately X X X X X X X
X X X X X X X
Yes
any one
Very
ITEM C. 'When they (each interference) how annoyed does this make you feel?'
ITEM B. "Do aircraft ever (interference listed below)?' If yes, ask C.
X - X
Very much Moderately
ITEM A. 'Tell me how much the noise of the aircraft bothers or annoys you?'
any one
) +1
SUM R I G H T - H A N D C O L U M N TO OBTAIN ANNOYANCE SCORE (Range of 0 to 6)
w
--]
+1
~- +1 m
X X X X X
(ITEM C) +1 +1
Not at all
(ITEM B)
~+1
--
A little
Construction of The Annoyance Scale (Responses Corresponding To X Score + 1 As Indicated) Oo
t~
Critique of subjective responses o[ Chinese to aircraft noise
229
TABLE 2
Percentage of Respondents Very Annoyed or ModeratelyAnnoyed by Interferenceof Aircraft Noise with Various Activities Hong Kong Speech interference Listening to radio/TV House vibrates Other interference Wake up Startle
28 21 7 7 11 9
Heathrow 1961
1967
20 25 18 6 25 25
24 32 19 12 19 13
From reference 1. could mean that the Hong Kong population might not be annoyed by having their activities interfered with--part of their lower sensitivity to noise, as claimed by the authors. But it could equally mean that many of the Hong Kong respondents did not experience these interferences. For example, Hong Kong respondents, nearly all of whom were on the ground floor level of multi-storey concrete buildings, may not have experienced the "house vibrating' in the way their Heathrow counterparts, living in detached, semi-detached or row housing, might have. Further, some proportion of respondents were interviewed in commercial premises (personal communication from the authors, I OA Meeting (HK Branch), March, 1963). (Much of the study area has a mixed land use with ground floor levels of the high-rise residential buildings used for commercial purposes.) These respondents worked in the commercial premises but would not necessarily have resided in that building, and those of them who lived outside the study area presumably would not have reported being awoken by aircraft noise. In commercial premises one might also expect that activities associated with commercial pursuits may dominate over the essentially domestic activities included in the annoyance scale. Respondents who could not experience specific activity interferences could not, of course, report annoyance with such interferences and so contribute towards their Annoyance Score. While all this is conjectural, without information on the comparative frequency o f activity interferences in the Hong Kong and Heathrow populations, as distinct from the frequency o f annoyance with activity interferences reported in Table 2, the possibility remains that the application of this particular type
230
A. L. B r o w n
of annoyance scale in the different physical environment of Hong Kong may have resulted in a downward bias in Annoyance Scores, vis-a-vis the Heathrow scores, quite unrelated to any difference in sensitivity to noise.
ATTITUDE TO QUESTIONNAIRES Thirdly, there are two results from the Hong Kong social survey which raise further questions about the comparability of the Hong Kong and Heathrow results--not in terms of a cultural difference in sensitivity to noise, but perhaps one of a cultural difference in response to questionnaires. In the questionnaire, opportunity was provided for respondents to spontaneously mention hearing aircraft noise. This was followed by a specific prompt as to whether respondents ever heard aircraft. There remained, after the second question, 23.3 per cent of the Hong Kong sample who never heard aircraft; a remarkable result given that the lowest aircraft noise exposure experienced was about 40 NNI. The equivalent figures in the 1961 and 1967 Heathrow studies were 3 per cent and 6 per cent, respectively, but at Heathrow the population included respondents with an exposure as low as 15 NNI. If almost a quarter of the Hong Kong sample did not hear aircraft despite very direct questioning, why not? Is the physical environment in Hong Kong sufficiently different, particularly at the ground floor level, that many respondents could not hear aircraft? If so, this would lend credence to the above argument regarding frequency of activity interference. Or could respondents, for their own purposes, have opted for the most neutral response, 'no'? This is discussed further below. In any case, a finding that a quarter of respondents in a dose-response study for aircraft noise did not 'hear' the dose should have been a cause for alarm to a researcher (was the dose measured adequately?) and certainly have prompted caution in comparing results with those of another study. Respondents were also asked another question: 'On the whole, would you say that you were more bothered by aircraft in the past, or have you got used to them?' The responses are not of interest here, except for the 28 per cent of respondents who did not offer an opinion, preferring to report ~don't know'. In the Heathrow surveys, the equivalent 'don't know' responses were only 4 per cent (1961 survey) and 1 per cent (1967 survey). The authors of the Hong Kong study comment: 'The high percentage of
Critique of subjective responses of Chinese to aircraft noise
231
"don't knows" implies the non-committal characteristics of the Chinese in Hong Kong'. They do not, however, draw the logical conclusion that if their respondents had been non-committal in one part of the questionnaire, they are quite likely to have been similarly inclined in others, including the component questions of the annoyance scale. Before a respondent could score on any of the activity interferences of Item C of Table 1, he had to be sufficiently willing to answer affirmatively to Item B. A low Annoyance Score resulting from a respondent's cultural propensity to being non-committal in a survey interview is something very different from a low Annoyance Score resulting from insensitivity to noise. It suggests that the social survey instrument, developed for the population around Heathrow airport, may not have been a suitable instrument for measuring the true effect of noise on the Chinese community living near the Hong Kong airport. CONCLUSION In conclusion, the authors are to be commended for attempting a comparative analysis of response across two different airports and two different cultures. The study of dose-response relationships for transportation noise sources has certainly been hampered by the multiplicity of measurement instruments, both for dose and for response, adopted by different researchers. However, it is unfortunate that this attempt has not been tempered by an understanding of the pitfalls of imposing a social survey instrument developed in one environment on another, and on the necessity for rigour when drawing conclusions on the differences between populations based on sample data. One needs to be particularly careful where premature conclusions about a population's sensitivity, or, in this case, insensitivity, to noise could become encoded in legislative and planning control which may relegate that population to high levels of noise exposure into the foreseeable future. REFERENCES 1. N. W. M. Ko and P. C. K. Lei, Subjective responses of Chinese to aircraft noise. Applied Acoustics, 15 (1982), pp.251 61. 2. Anon., Command2056 Noise: Final Report of the Committee on the Problem of Noise, HMSO, 1963.
232
A. L. Brown
3, E~ Jones and D. J. Sinclair, Atlas oJ London and the London Region, Pergamon, Oxford, 1968. 4. Hong Kong, Population Map 1:350,000. Series AR/2/P, 1978. 5. J. Neter and W. Wasserman, Applied linear statistical models, Richard Irwin, 1974. 6. R. E. Walpole and R. H. Myers, Probability and statisticsjor engineers and scientists, Collier MacMillan, 1972. 7. J. Cohen and P. Cohen, Applied multiple regression/correlation analysisjor the behavioral sciences, Lawrence Erlbaum Associates, 1975. 8. Anon., Second survey of aircraft noise annoyance around London (Heathrow) Airport, HMSO, 1971. 9. A. C. McKennell, Aircraft noise annoyance around London (Heathrow) Airport, Central Office of Information, SS Report 337, HMSO, 1963.