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|Year : 2014
: 16 | Issue : 69 | Page
|Neighborhood noise pollution as a determinant of displaced aggression: A pilot study
Angel Dzhambov1, Donka Dimitrova2
1 Faculty of Medicine, Medical University of Plovdiv, Plovdiv, Bulgaria
2 Department of Health Management, Health Economics and Primary Care, Faculty of Public Health, Medical University of Plovdiv, Plovdiv, Bulgaria
Click here for correspondence address
|Date of Web Publication||7-May-2014|
Noise pollution is still a growing public health problem with a significant impact on psychological health and well-being. The aim of this study was to investigate the impact of noise on displaced aggression (DA) in different subgroups of residents in one of the neighborhoods of Plovdiv city. A cross-sectional semi-structured interview survey was conducted using specially designed data registration forms and 33 close-ended and open-ended questions, divided into two major panels - one original and a modified version of the Displaced Aggression Questionnaire (DAQ). The mean score for DA was 61.12 (±19.97). Hearing noises above the perceived normal threshold, higher noise sensitivity and continuous noises were associated with higher levels of DA. Low frequency and high intensity noises were also associated with higher DA scores. Multiple regression model supported these findings. Contradictory to previous research age was positively correlated with noise sensitivity and aggression. We speculated that this might be due to the relatively lower socio-economic standard and quality of life in Bulgaria. Therefore, social climate might be modifying the way people perceive and react to environmental noise. Finally, the DAQ proved to be a viable measurement tool of these associations and might be further implemented and modified to suit the purposes of psychoacoustic assessment.
Keywords: Displaced aggression, neighborhood, noise pollution
|How to cite this article:|
Dzhambov A, Dimitrova D. Neighborhood noise pollution as a determinant of displaced aggression: A pilot study. Noise Health 2014;16:95-101
| Introduction|| |
Noise pollution is one of the current public health problems associated with urbanization and modern life. A recent publication of the Regional Office for Europe of the World Health Organization estimated that applying the epidemiological measure of disability-adjusted life years at least 1 million healthy life years are lost every year from traffic-related noise in the Western Europe.  Noise levels above 55 dB are considered disturbing for the hearing comfort. Noise is a common cause for psychological distress, cognitive impairment, sleep disturbances, increase in social conflicts, anxiety, nervousness, emotional instability, argumentativeness, etc. ,,, Even at levels that are not harmful to the hearing, it is perceived subconsciously as a danger signal, even during sleep.  Noise pollution continues to grow in extent, frequency and severity as a result of population growth, urbanization and technological developments. 
The effects of noise were found to be strongest for annoyance.  Living along arterial urban streets increased risk of noise annoyance by 40%.  In their study Bluhm et al., stated that starting at about 57 dB, there was a large increase in percentage of people annoyed by sound  and Öhrström et al., found that at higher dB levels (65 dB), 75% of people were annoyed by road traffic noise. 
In some experimental studies aggression was found to be directly related to noise and annoyance.  Other authors do not believe that noise exposure per se could produce aggressive behavior. In combination with provocation, pre-existing anger or hostility, etc., however, noise could trigger aggressive behavior. ,
Investigations on the topic of aggression have been constrained to instances of direct aggression, which is retaliation toward the provoking agent.  This also implies the relationship noise - aggression. We hypothesized that a new measure of noise induced aggression had to be utilized in order to study the indirect noise induced aggressive behavior of all community members, including elderly people, women, severely impaired, etc. who are unlikely to directly retaliate toward a provoking agent but who still suffer the health and psycho-social consequences of it. We believe that displaced aggression (DA) is such measure. It occurs when a person is provoked, is unwilling or unable to retaliate against the original provocateur and subsequently aggresses against a seemingly innocent target.  Individuals high in trait DA may be especially prone to experiencing physical health problems,  as well as to undermining the human capital of other community members and relatives, that affects health and well-being.
In Bulgaria community aggression is common, but its associations with neighborhood noise pollution still lack scientific grounding. On the other hand, the proportion of elderly and impaired people is constantly rising.  Having in mind all of this, we aimed to investigate the impact of noise on DA in different subgroups of residents in one of the neighborhoods of Plovdiv city - one of the most populated Bulgarian cities, high in traffic and neighborhood confrontation.
| Methods|| |
During the period of 1 June to 1 July 2013, a cross-sectional semi-structured interview survey was conducted amongst residents in one of the neighborhoods of Plovdiv city. We used a two stage random sampling method. To determine the sample size in the first stage of the study a pilot run results from 30 residents were used to determine the standard deviation (SD) and relative shares for the quantitative variable of greatest interest: Total score for 20-item Displaced Aggression Questionnaire (20-item DAQ). The determined number of participants calculating for 95% degree confidence and an error of 5% from the mean value of the score was 150. After adjusting for the expected non-response rate, we determined that 225 participants were to be recruited. Totality of 226 residents were contacted and the response rate was 84% (n = 190).
The survey was voluntary and anonymous, sociomedical, non-interventional and self-report and therefore was not subject to ethical evaluation by our University. It was carried out after obtaining participants' informed consent about the objectives and conditions of the study.
Methods of selection
In order to determine the noisiest non-industrial neighborhood we undertook a widely accepted strategy. We used data from the online noise monitoring system of Plovdiv Municipality. , The city of Plovdiv (42°9′N, 24°45′E) is the second-largest city in Bulgaria with a population of 339,077 inhabitants as of December 2012 and a territory of 101.98 km 2 . The studied neighborhood is located in the Eastern district of the city, which has 61,149 inhabitants, a territory of 6.34 km 2 , 9644.95 people/km 2 and 11.5 m 2 roadways per capita. In the neighborhood, the main type of housing is 6-7 storey residential blocks. It should be noted that in this neighborhood is located the central cemetery of the city.
For the assessment of traffic noise the French National Method "NMPB-Routes-96" and the French standard "XPS 31-133" were used. Sound levels were measured with "Bròel and Kjær Type 2240" sound meter and "Brüel & Kjær Type 4231" calibrator. We also used satellite images in order to determine the radius of interest around the noise monitoring station [Figure 1].  The selected neighborhood was situated in approximately 600 m radius of the noise monitoring station, on the both sides of one of the boulevards with most intense traffic and leading to a highway. On May 15, 1000 cars/h and 100 trucks/h were registered on that boulevard and the traffic-generated equivalent continuous noise level (L Aeq ) was 71.9 dB. Overall neighborhood L Aeq during the last 3 months (1 March to 1 June 2013) was above 60 dB with maximums of approximately 80 dB. The sound level meter was "Brüel & Kjær 3639-E-100".
|Figure 1: Satellite image of the neighborhood where the study was conducted|
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A couple of students were recruited to help the authors with data collection and compensated with 10 leva (5 euros) a day for their time. They were instructed how to interview the residents of the neighborhood asking them to think about the last 3 months when answering the questions. The interviewers started their routes in four directions from the terminal location. They selected one individual over 18 years in every third household. If there was more than one person in the household, the one, whose birthday was closest to the date of the beginning of the survey was invited to participate. The interviews took place at a convenient time (5-8 p.m.) at residents' homes. In order to minimize reporting bias we presented the aim of the interview as assessment of residents' attitude toward noise pollution, because the word "aggression" is somewhat suggestive and concerning in Bulgarian.
Especially designed data registration forms and 33 close-ended and open-ended questions, divided into two major panels, were used. First panel comprised three original batteries assessing demographic and health characteristics, noise sensitivity and noise characteristics. The second panel was a modified version of the DAQ, comprising only "Angry Rumination" and "Behavioral DA" subscales because we found the "Revenge Planning" subscale unsuitable for our purpose (Courtesy of Assoc. Prof. Denson). , Because DA is usually provoked by another person, in our study it would not be relevant to attribute such properties to noise as a phenomenon. The summary composite score of the two retained subscales was used as an indicator of DA and will be referred to when DA is discussed further in this paper. All items were rated on bipolar seven-point Likert-type scales ranging from 1 (extremely uncharacteristic of me) to 7 (extremely characteristic of me). The English version of the questionnaire was adapted and translated according to guidelines that are widely accepted for the successful translation of instruments in cross-cultural research - translation, back-translation and a pretest with a representative sample. ,,
Inclusion criteria: Adults dwelling in the neighborhood for at least the past 3 months. Exclusion criteria: Decline to participate, dwelling for <3 months, incomplete completion of the data registration form, minors.
Descriptive statistics, parametric and non-parametric analyzes were performed. When appropriate, ordinal and nominal data was transformed into numeric. To check the normality of the distribution the D'Agostino-Pearson K2 test was used. Mann-Whitney test was used for comparison of quantitative variables in independent samples with distribution other than normal. Pearson and Spearman's correlation analyzes were used to assess the correlations between "20-item DAQ score" and variables from "demographic", "noise acoustical characteristics" and "noise sensitivity" panels. When testing hypotheses for incidental (accidental) effect of a factor, Fisher's exact χ2 test and the criterion for significance level of P < 0.05 (two-tailed) were used. The main analysis was multiple linear regression. Results are presented as the number and percentage, mean and ±SD and correlation coefficients. Graphical analysis was applied as well. Statistical data processing was performed using the software SPSS v.17 (SPSS Inc., 2008. SPSS for Windows (17.0.0), Chicago, USA).
| Results|| |
Out of the 190 people interviewed eight were excluded based on exclusion criteria (incomplete completion of the data registration forms by the interviewers). The excluded participants represented only 4.2% of the sample and therefore they did not have to be compared with the included participants and did not affect the statistical processing. The remaining 182 residents were included in further statistical analyses.
The characteristics of the participants are presented in [Table 1]. The mean age was 36.93 (±18.13) years where the youngest participant was 18 years old and the oldest - 92 years old. The majority were 21-40 years old. No significant differences were found in reference to sex. Nearly half of the participants had bachelor or master's degree, followed by those with upper secondary education. More than a half were married or were living with a spouse. We believe that the demographic profile of the residents, although not homogenous, somewhat representative of the studied population and corresponds with their age structure. This was supported by the direct observations of the interviewers. However, there are no official records for Plovdiv demographics on the neighborhood level because it is too small unit. Assessing the "Municipality plan for development of Plovdiv 2005-2013" confirmed our findings regarding the representativeness of the sample for the Eastern district population, although some discrepancies are due to the fact that we included only individuals over 18 years of age and the official data is from 2001. "Occupation", "health status" and "years of residency" were also explained to a great extent by the age of the participants. We hypothesized that the latter factors could be confounders in reference to the level of aggressiveness and predicting the outcome and hence, had to be explored.
The scores for the 20-item DAQ approximated normality sufficiently to be included in parametric tests (K2 = 6.488, P = 0.039). The mean was 61.12 (±19.97) with a minimum of 23 and a maximum of 113 points. The mean scores for the "Angry Rumination" and "Behavioral DA" subscales were 31.73 (±11.05) and 29.4 (±9.17), respectively.
As shown in [Table 2], the "noise panel", aimed to examine the self-reported noise sensitivity and annoyance, the idea of normal and abnormal noise levels and some of the acoustical characteristics of noise. In reference to the latter, the interviewers explained to the participants "noise frequency", "noise intensity" and "type of noise exposure" by giving them common examples from everyday life (a turbine sound, train, truck, whistle, vacuum cleaner, etc.).
|Table 2: Noise sensitivity, noise characteristics and 20-item DAQ scores|
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As an introduction to the main analysis, at [Table 3] is presented the correlation-matrix for DAQ and other demographic and noise-related variables of interest.
|Table 3: Correlation-matrix for the demographic and noise related variables associated with displaced aggression|
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We will comment on the correlations of interest from [Table 3]. It was found that DAQ was higher in women and in older people living in the neighborhood for a longer time, in people with better education and in those reporting poorer health (the positive coefficient is due to reverse coding of the variable). Moreover, low frequency and continuous noises resulted in more DA. The frequency of hearing noises above the normal threshold was positively correlated with DA as was noise annoyance. Only a small part of the participants reported "very high" noise sensitivity, but it was the strongest correlate of DAQ.
In order to seek for a model predicting the higher values of the 20-item DAQ, we performed a multiple regression analysis with "total 20-item DAQ score" as dependent variable logically associated with it as predictors - "perceived sensitivity to noise", "type of noise exposure", "frequency of hearing noises above the normal threshold", "annoying noise frequency", "age" and "years of residency". They were all entered simultaneously [Table 4]. We also included an interaction-term of "age" and "years of residency" in order to find whether there could be an explanation for the higher DA in senior citizens. The model showed with 64% power of prediction that the significant factors determining DA levels were "perceived noise sensitivity", "type of noise exposure" and "frequency of hearing neighborhood noises considered above the normal threshold".
|Table 4: Coefficients for multiple regression model predicting the 20-item DAQ score from "perceived noise sensitivity", "type of noise exposure", "noise frequency", "frequency of hearing noises above the normal threshold", "age", "years of residency" and an interaction-term (age×years of residency)|
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The age and years of residency of the participants were not significant predictors of DA when included in the model along with the noise characteristics. Moreover, the effect of age did not vary across values of "years of residency" (P < 0.05 for interaction-term), suggesting it was not a moderator of that effect.
| Discussion|| |
The analyses of the "demographic panel" demonstrated that women, older people, those living in the neighborhood for a longer time, those who were retired, with higher educational level and poorer health, were prone to higher levels of DA. These findings indicated that age, which is determinant of the other factors to a greater extent, is probably the key confounding factor correlating with DA. The fact that in our study age was positively related to both noise sensitivity and DA, in contrast to the findings of other authors,  could not be explained by years of residency as a possible moderator. However, we speculate that this is due to several reasons. There is a steady trend over the last decade for increasing the rate of elderly people at risk of poverty in Bulgaria.  Moreover, the health care system in the country needs serious reforms and currently does not function as it should.  Elderly people are often deprived of basic medical care and social acceptance and are generally more dissatisfied with their lives.  Having all of this in mind, we hypothesize that various social antecedents of noise sensitivity and aggression confound our findings and are responsible for the discrepancies with other authors'. In addition, the fact that the neighborhood was located close to a cemetery could have additional psychological impact on the assessed constructs of DA and noise sensitivity, which should also be addressed in future research.
Following this line of thoughts, we could say that better education was associated with higher DA, simply because it was a function of age. Moreover, such discrepancies may occur in cross-cultural research especially when the measures are taken in countries with diametrically different social standards. Nevertheless, it was beyond the scope of this paper to study in detail these inter-relationships and this should be a topic for a follow-up study.
The more often people were hearing noises above the normal threshold, the more noise sensitive they considered themselves to be and the more annoying they considered the neighborhood noises-the higher levels of DA. Low frequency, high intensity and continuous noises were associated with significantly higher levels of DA. The regression model supported these findings suggesting that frequent interaction with continuous noises in combination with higher noise sensitivity could be predicting the majority of urban DA in non-industrial neighborhoods. This was true even after controlling for age and years of residency, which were also significantly correlated with DA. However, age and years of residency were not significant predictors when included in the model. In follow-up studies structural equation modeling might help to uncover some unmodeled relationships between these variables.
It should be noted that because of the cross-sectional design of the study and the lack of different noise condition groups, the actual noise exposure could not be included as a predictor in the model. On the other hand, we do not consider this fact particularly troublesome because noise sensitivity is not predicted by noise exposure but rather by personality traits and psycho-social experiences.  Annoyance, which has acoustical antecedents, is mainly conditioned by noise sensitivity, which is a stronger predictor of annoyance than noise and can predict it above and beyond noise exposure, probably by moderating their relationship. , Thus, it can be argued that because in our sample noise sensitivity was the strongest DA predictor, noise exposure was irrelevant. Moreover, it might be hypothesized that the psycho-social antecedents of noise sensitivity (the mentioned above low quality of life in Bulgaria) are causing higher DA through noise sensitivity, which on the other hand moderates the effect of noise exposure on annoyance thus resulting in higher DA. It was beyond the scope of this study to reveal these associations, but they are very plausible and by setting ground for their research this paper contributes to the field of psychoacoustics.
Although our study undertook a novel approach toward a better understanding of the psycho-social impact of noise pollution, we confirmed the findings of other authors about the significant contribution of noise to annoyance. ,,,, Noise may not be the sole predictor of aggression,  as there are some social and demographic confounders, but in combination with them it is associated with higher levels of DA, which could be harmful to the psycho-social well-being of people. Residents with poorer health presented with higher levels of DA, which is considered a possible contributor to physical health problems,  but we failed to determine the causal relations between the two variables. We confirmed that low frequency noises were more annoying and resulted in more substantial DA.  Elderly people were also found to be more susceptible to noise annoyance and DA. , Secondary analysis of the collected data might elucidate other intrinsic aspects of psycho-acoustical perception.
The cross-sectional design of the study does not permit us to determine causal sequences between the assessed variables; the cross-cultural validation protocol for the 20-item DAQ did not assess internal consistency of the subscales; not all cultural and psychological factors of the participants were taken into consideration and might be possible confounders. Finally, a measure of socio-economic class could not be included due to poor reporting for this variable in particular, as it is a sensitive topic for many Bulgarians.
Future studies should replicate our results utilizing designs capable of establishing causal relationships, larger samples and assessing the psycho-cultural characteristics of the residents. Our results could help politicians, health care managers and other researchers better understand the psychology of neighborhood acoustics and to implement DA as a reliable measure for the indirect negative social and health impact of noise pollution.
| Conclusions|| |
DA is strongly associated with continuous noise exposure and subjective susceptibility to noise. It is influenced by some of the acoustical properties of noise as well. With age and impairment of their health people living in lower socio-economic conditions might become more noise sensitive and prone to DA. Therefore, the social climate might be affecting the way people perceive and react to residential noise. The 20-item DAQ proved to be a viable measurement tool of these associations and should be further implemented and modified to suit the purposes of psycho-acoustical assessment.
We hope that our results will point the attention to this underestimated environmental problem that has only in the recent years raised concern among Bulgarian health care politicians. By assessing the responses of citizens to different urban settings more active and evidence-based decisions could be made improving the infrastructure of the endangered neighborhoods. In addition, an interdisciplinary public health approach should be taken in order to counteract the damage of noise pollution using validated programs for coping with psychological distress and preventing social confrontations.
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MMSc student, Faculty of Medicine, Medical University of Plovdiv, No. 15-A, "Vasil Aprilov" Blvd., 4002 Plovdiv
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2], [Table 3], [Table 4]