1 Linking traffic noise, noise annoyance and life satisfaction: a case study Abstract: The primary purpose of this study is to explore the link between traffic noise and overall life satisfaction. While a negative relationship between residential satisfaction and traffic noise is relatively well established, much less is known about the effect of traffic noise on overall life satisfaction. We hypothesize that the relationship between traffic noise levels and life satisfaction is mediated by noise sensitivity, noise annoyance and residential satisfaction so that the direct relationship between noise exposure and life satisfaction may be actually attenuated. The empirical model is tested using structural equation modeling. Our study exploits data on a sample of respondents living in areas with high road-traffic noise and another sample of respondents living in areas exposed to high levels of rail traffic noise. The data contained information about average traffic noise levels (Lden) at the address points, noise annoyance, subjectively perceived noise sensitivity, residential satisfaction and life satisfaction. The proposed empirical model fits the data on road-traffic noise and rail traffic noise extremely well. Our results suggest that a link between life satisfaction and traffic noise exposure exists, however it is mediated by noise annoyance and residential satisfaction, but not noise sensitivity. Keywords: traffic noise, noise annoyance, life satisfaction, residential satisfaction 1. Introduction Environmental noise and particularly persistent and high levels of transportation noise have been shown to have considerable effects on health and well-being (Berglund, Lindvall, &Schwela, 1999; Berglund, Lindvall, Schwela, &Goh, 2000; WHO, 2009). According to WHO, one third of EU citizens is annoyed due to environmental noise and about 25% of EU citizens experience sleep disturbances due to environmental noise (WHO, 2010). Road-traffic noise seems to be an important source of noise in the EU as in 2000 some 44% of the citizens of the EU 25 countries were exposed to road-traffic noise levels exceeding 55dB (Den Boer & Schroten, 2007), a level at which “health effects occur frequently, and a sizable proportion of the population is highly annoyed and sleep-disturbed” and for which “there is evidence that the risk of cardiovascular disease increases” (WHO, 2011, p. 58).Railway noise seems to be a lesser problem than road-traffic noise as only 7% of the EU 25 citizens were exposed to noise levels exceeding 55 dB in 2000 (Den Boer & Schroten, 2007). Indeed, exposure to the same level of railway noise is likely to result in less annoyance in comparison to road-traffic and aircraft noise as documented by exposure-response functions based on meta-analysis of empirical studies of noise annoyance (EU, 2002; H. M. Miedema & Oudshoorn, 2001), possibly with the exception of high-speed trains in Korea and 2 Japan, which produce more noise annoyance at the same noise level (Lim, Kim, Hong, & Lee, 2006; Morihara, Yeno, & Sato, 2002). Despite this type of evidence, relatively little is known about how road-traffic and rail-traffic noise affects overall life satisfaction. The purpose of this paper is to fill this gap by linking together different concepts that have appeared in empirical literature, proposed a unified model and submit this model to an empirical test. Specifically, this paper aims to link noise exposure, noise sensitivity, noise annoyance, residential satisfaction and overall life satisfaction. 1.1. Noise annoyance and noise sensitivity Environmental noise is unwanted sound caused by emissions from traffic and industrial and recreational infrastructures, which may cause annoyance and health damage. The noise originating from transport is a classical nuisance or an externality in economic terms. This is a spill-over effect of an activity which affects the welfare of others, without being compensated by the producer of such an externality. One of the effects of noise exposure on the well-being of human consists in noise annoyance defined as "a feeling ofdispleasure associated with any agent or condition, known or believed by an individual or group to adversely affect them"(Lindvall & Radford, 1973). According to Miedema, noise annoyance is "a sensitive indicator of adverse noise effects and by itself means the noise affects people’s quality of life" (Miedema, 2007). Thus, noise annoyance appears to mediate some of the health effect of noise exposure (A Fyhri & Klaboe, 2009). Over the last 40 years a substantial volume of literature has provided evidence on relationships between level(s) of noise exposure and expected noise annoyance. In a seminal synthesis, Schultz (1978) translated exposure-response relationships from several social surveys into common day-night average sound levels and proposed the average of those relationships as a means for predicting community annoyance from transportation noise. Miedema and Oudshoorn (2001) later developed a more elaborated model to predict three levels of noise annoyance for road, rail and aircraft noise for two alternative noise metrics, day-night level (mostly used in the USA) and day-evening-night level endorsed in the EU’s Environmental Noise Directive. In a recent study for the Danish Ministry of Science, Technology and Innovation (Pedersen and collaborators 2007) developed logistic functions for annoyance exposureresponse relationships with various covariates representing the effects and parameters of noise sources, locations, activities, perceived acoustic attributes and non-acoustic factors. These noise exposure functions, which describe in probabilistic terms the relationship between noise exposure and noise annoyance, typically consider noise exposure values between 45dB and 75dB in order to avoid uncertainties. Noise annoyance is currently one of the most extensively studied metrics for assessment of environmental noise impacts on people. The ISO standard 15666:2003 provides a 5-level scale of annoyance (not annoyed, slightly, moderately, very and extremely) for socio-acoustic and social surveys on noise effects (for details see method section of this paper). Noise annoyance is influenced by many factors besides noise exposure, including person-related variables (age, stress level, duration of exposure to noise, noise sensitivity), house-related variables (floor, number of windows oriented towards the source of the noise), and the characteristics of noise source there (traffic 3 flow during the day and night) (Jakovljevic, Paunovic, & Belojevic, 2009). Noise sensitivity is probably the most important non-acoustic factor of noise annoyance (Aslak Fyhri & Klæboe, 2009; Guski, 1999; Jakovljevic et al., 2009; Job, 1999; H. Miedema & Vos, 2003; Paunović, Jakovljević, & Belojević, 2009; Weinstein, 1978; Zimmer & Ellermeier, 1999) while socio-demographic factors usually play a minor role (Schreckenberg, Meis, Kahl, Peschel, & Eikmann, 2010). As a matter of fact, noise sensitivity itself seem to be independent of noise exposure and rather related to the psychological characteristics of individuals(Schreckenberg et al., 2010). 1.2. Life satisfaction Happiness, subjective well-being, life satisfaction, and quality of life are some of the terms that appear interchangeably in the literature to denote evaluation of one's life as a whole (Frey & Stutzer, 2002; Tella, MacCulloch, & Oswald, 2003) or specific aspects of life (Andrews & Withey, 1976). The concept of "overall" life satisfaction that we focus on in this paper originated in psychology and sociology, but recently has made its way also into economics where it is used as a measure of "experienced utility" (Kahneman & Sugden, 2005) and applied in a number of empirical studies that aim at monetary valuation of non-market goods (see, e.g., Praag & Ferrer-i-Carbonell, 2008 for the overview of this approach). Since "overall" life satisfaction is an evaluation of one's life a whole, basically anything that we can think of can potentially influence it. Empirical studies show that many economic variables such as income, unemployment, and inflation are predictive of life satisfaction (Clark & Oswald, 1994; Easterlin, 2001; Frey & Stutzer, 2002; Tella, MacCulloch, & Oswald, 2001) as well as factors that characterize one's socio-demographic situation (age, gender, parenthood) and health status (Rehdanz & Maddison, 2008). Recent research has shown that besides the socio-demographic and economic variables also ambient environmental quality affects life satisfaction. It has been found that climatic conditions affect life satisfaction at the country-level aggregation (Rehdanz & Maddison, 2005)and also at the individual level (Brereton, Clinch, & Ferreira, 2008; Frijters & Praag, 1998). Similarly, air pollution has been found to affect life satisfaction at the aggregated country level (Welsch, 2002, 2006, 2007) and also at the individual level (Ferreira, Moro, & Clinch, 2006; MacKerron & Mourato, 2009); one study known to us also found an effect of perceived air pollution on the individual quality of life (Rehdanz & Maddison, 2008). Surprisingly little is known about the effects of noise exposure on life satisfaction. As far as we are aware, only the study by Van Praag and Baarsma (2005) examined and found an effect from exposure to aircraft noise on individual life satisfaction. Another study has examined the effect of perceived noise-related adverse effects on life satisfaction (Rehdanz & Maddison, 2008), but found this effect only for some of the model specifications which may lead one to infer that the effect is not particularly strong. Besides the studies of the effect of noise on overall life satisfaction, there are several empirical studies that focus on the effect of noise exposure and noise annoyance on satisfaction with some aspects of one's life (as opposed to satisfaction with life as a whole). Probably the most studied aspect of life satisfaction found to be related to noise is residential satisfaction or one's satisfaction with the quality of life in a specific area. A study by Botteldooren et al. (2011) has found the effect of traffic noise exposure on residential quality. The study by Schreckenberg et al. (2010) has examined the effects of exposure to aircraft noise 4 and related noise annoyance on different aspects of quality of life (i.e., satisfaction with dwelling, residential area, infrastructure, quietness, and attractiveness of the residential area) and found that there was a significant negative effect of noise exposure on the attractiveness of the residential area and the total score of residential satisfaction, and also a significant effect of noise annoyance on satisfaction with dwelling). A study by Kroesen et al. (2010) has found an effect of exposure to aircraft noise on residential satisfaction mediated by noise annoyance. Several other studies have also investigated the effects of noise exposure and noise annoyance on healthrelated aspects of life satisfaction. The study by Shepherd et al. (2010) has found the effect of aircraft noise, mediated by annoyance, on life satisfaction (or the quality of life as the authors term it), a multidimensional construct that included physical health, psychological well-being, social relationships and environmental factors. The study by Dratva et al. (2010) has found an effect from road-traffic noise on all aspects of health-related quality of life (physical functioning, role-physical, bodily pain, vitality, social functioning, role-emotional, mental health) except for general health (Dratva et al., 2010). 2. Data and method 2.1. Data The data exploited in this paper come from a survey conducted in summer 2009 in five cities in the Czech Republic (Prague, Vysoke Myto, Ceska Trebova, Mnisek pod Brdy, and Koprivnice) using combination of purposive and stratified random sampling. The five cities were chosen to represent rail and road transport modes, cities of different sizes and with different transport networks (viz. figure 1). Based on the noise maps, obtained from National Reference Centre for Community Noise, Transport Research Centre and AkustikaPraha, we have chosen in each of the cities several localities exposed either to road-traffic noise or to rail-traffic noise, but not to both. In each of these localities a random sample of address points was drawn. At each of these addresses, interviewers chose randomly the floor of the house, specific housing unit and a respondent within that house using Kish sampling method tables (Kish, 1995). Since we know the address points, we can attribute to each respondent the noise level he or she is exposed to. The data were collected using in-person interviews in respondents' homes. In total 609 questionnaires were collected, out of which 363 in areas exposed to road-traffic noise and 246 in areas exposed to railway noise. However, for 9 respondents exposed to road noise (all but one from Prague) and 18 respondents exposed to railway noise (all from Prague), the interviewers failed to report their precise address and therefore we could not attribute the noise levels for these respondents. In consequence, we included in the final analysis 354 respondents exposed to road-traffic noise and 228 respondents exposed to railway noise. The average age of respondent in our sample is 47.4 (min. 18, max. 88) and did not differ across the cities (F=0.515, df=4, p=0.72) or the type of noise burden, i.e. road vs. railway (F=0.525, df=1, p=0.52). On average, 6.7% of our respondents had received only elementary education, 30.3% high-school education without the state leaving exam, 42.1% high-school education with state leaving exam, 4.93% completed college education and 16.0% had received an education degree; this proportion is similar across the two types of noise burdens (2=1.956, df=5, p>0.05) but not across the five cities (2=47.6, df=20, p<0.001). A 5 close look at the contingency table (not reported here to save space), reveals that respondents in Prague were more often university-educated and they were less likely to have elementary education only, and that respondents in Koprivnice were less likely to have a university degree. These irregularities are given by the fact that Prague is large city that hosts several universities and attracts university-educated people, while Koprivnice, a town of 22,800 inhabitants and once an important car-manufacturing centre (Tatra Koprivnice) which still substantially relies on industrial production. Males represented 58.1% of our sample and their proportion was similar across the two types of noise burden (2=0.7, df=1, p=0.4) and across the five cities (2=4.81, df=4, p=0.31). Figure 1: Towns included in the survey Note: 1. Mnisek pod Brdy (4,700 inh.), 2. Prague (1.2 million inh.), 3. Vysoke Myto (12,400 inh.), 4. Ceska Trebova (16,000 inh.), 5. Koprivnice (22,800 inh.). 2.2. Measures The noise data were taken from strategic noise maps drawn up pursuant to EU Environmental Noise Directive and refer to base year 2006 because newer noise data were available. We made no adjustments to reflect changes that may have taken place in-between such as change in traffic, installation of noise barriers, laying of silent pavements, introduction of new speed limits etc. because information concerning these changes is very scarce. The fact that 3 years has passed between the time of measurement of objective noise levels and the time of our survey may bias results and we acknowledge this limitation. Unfortunately, no newer data of comparable quality were available and will only be available after the 6 completion of 2012 strategic noise mapping. Nonetheless, as we argue in the concluding section of this paper, even with this limitation we think that the data capture the overall trend sufficiently. To capture noise exposure, we have opted for the 24-hours composite noise indicator Lden that is nowadays a common reference of objective noise level used in socio-acoustic research (EC, 2002; H. M. Miedema & Oudshoorn, 2001)and as such provided in strategic noise maps. To measure noise annoyance, respondents were given the following question: "When you are at home are you annoyed by road-traffic/ railway noise?" (The source of noise was chosen depending on the principal noise burden.) A 5-point annoyance scale defined by ISO standard 15666:2003, with the answer categories "not annoyed", "slightly annoyed", "moderately annoyed", and "very and extremely" was then used to record respondents' annoyance. Although various measures of life satisfaction exist, it has been shown that this concept has a high degree of consistency, reliability, validity and stability over time (Diener, Suh, Lucas, & Smith, 1999). Indeed, it appears that different measures of life satisfaction do in fact converge and they seem to represent a single concept; they correlate with physical manifestations of happiness; people who express high life satisfaction are also more likely to be described as happy by other people and are less likely to commit suicide (Welsch, 2006, p. 803) We adopt in the present research a measure of life satisfaction proposed by Cantril (1966), which asks people how satisfied they are with their life as a whole. This question accompanied with an 11-point scale has become almost a standard in life-satisfaction research and has been applied in a number of empirical studies (Carroll, Frijters, & Shields, 2009; Frijters & Praag, 1998; Luechinger, 2009; MacKerron & Mourato, 2009; Rehdanz & Maddison, 2008) although some researchers may prefer to use a shortened answer scale (cf. Rehdanz & Maddison, 2005; Welsch, 2006). The validity of this particular measure of life satisfaction has been has been demonstrated (Frey & Stutzer, 2002; Tella et al., 2003). There seems to be no agreement whether life satisfaction should be treated as a cardinal or ordinal measure, though it appears that in many applications accepting the assumption of cardinality or ordinarily will have negligible effect on empirical results (Ferrer-i-Carbonell & Frijters, 2004). To stay on the safe side, we decided to treat the variable as ordinal. Residential satisfaction is measured by asking respondents the following question: "All things considered, how satisfied are you with the life in the area where you are currently living? (Take into account the area within walking distance from your home.)". Respondents indicated their answers on a 11-point Likert-type scale ranging from 0 ("extremely dissatisfied) to 10 ("extremely satisfied"). Noise sensitivity is measured as respondents' perception of their sensitivity to noise. Respondents were asked the following question: "To what degree are you, in your opinion, sensitive to noise?" Respondents indicated their answers on a 4-point Likert type scale ranging from 1 ("very sensitive") to 4 ("I am not sensitive"). 2.3. Model 7 Based on the review of previous empirical research we propose the following empirical model (for its graphical representation in the form of a path diagram see figures 4 or 5 - we propose the same model in the road- and rail-traffic context). In the model we assume that noise exposure (observed continuous variable Noise) has an effect on noise annoyance (latent variable Annoy). This hypothesis is supported by the bulk of the noise annoyance literature discussed earlier. We also assume that noise exposure may have a direct effect on life satisfaction (latent variable Lsatisf) that is not mediated by Annoy. This hypothesis reflects the fact that noise annoyance is only one of several adverse effects on human well-being, albeit one of the most important (cf. WHO, 2011, p. 101). In addition, we assume that Noise may also have an effect on noise sensitivity (latent variable Sensit) - this would be, for instance, the case when noiseinsensitive people would move into areas with high noise exposure benefiting from their comparative advantage. We make this assumption is spite of the fact that previous research has not confirmed the effect of noise exposure on noise sensitivity (see, e.g., Schreckenberg et al., 2010). Nonetheless, we leave this question open to empirical investigation in our study. Further, we assume that noise annoyance has an effect on residential satisfaction (latent variable Rsatisf). This assumption is supported by a wealth of evidence from previous empirical studies (see, e.g., Botteldooren et al., 2011; Kroesen et al., 2010; Schreckenberg et al., 2010) . In addition, we assume that noise annoyance may have direct effect on life satisfaction unmediated by residential satisfaction. Finally, our models assume that residential satisfaction has an effect on life satisfaction (latent variable Lsatisf), this hypothesis is justified by the mere fact that residential satisfaction is one of the aspects of the overall life satisfaction. 2.4. Procedure The empirical models are tested using structural equation modeling (Bollen, 1989). SEM is very advantageous for the purpose of our study specifically because it allows us to examine a relatively complex model which includes continuous variable Noise and several latent variables indicated by ordinal outcome variables. As a matter of fact, SEM has been previously used with some success to analyze the link between noise exposure, noise annoyance and adverse psycho-physical effects of noise exposure(Aslak Fyhri & Klæboe, 2009). The core idea of SEM is that it is possible to reproduce a population variance-covariance matrix if we know the model which correctly explains variation in the data. Although different estimators may be used to estimate the model parameters, all estimators basically aim to minimize the discrepancy between the model-implied and empirical variance-covariance matrix of observed variables. Our model could be expressed as a series of 4 equations for each of the dependent variables. In the shortened matrix form, these equations can be re-expressed for each individual, i, as: 𝛈𝒊 = 𝐁𝛈𝒊 + 𝛅𝑁𝑜𝑖𝑠𝑒𝑖 + 𝛇𝒊 (1) where η (4 x 1) is a vector of endogenous latent variables (i.e., Sensit, Annoy, Rsatisf, and Lsatisf), Noise (a scalar), is the value of environmental noise (Lden) observed for each individual i, B (4 x 4) is a matrix of regression coefficients among η’s with the diagonal elements equal to zero and I-B, being a non- 8 singular matrix, (3 x 1) is a parameter vector of coefficients for the regression of latent variables η’s on Noise, and (4 x 1) is a vector of residuals that are assumed to have multivariate normal distribution. Note that in the model we fix the that refers to the influence of Noise on Rsatisf to 0 as we assume that Noise has no direct effect on Rsatisf (see also figures 4 and 5 where this is expressed in graphical form). We assume that j-th continuous latent variable, ηj, is measured without a measurement error by only one observed continuous outcome variable, y, expressed as i-th respondents' rating on j-th Likert-type scale. The probability of observing i-th respondent indicating values 0,1,...,S on this scale can be expressed using the following threshold ordered probit model (for technical details of this model see, e.g., B. Muthén, 1983): 𝑃 (𝑦𝑖,𝑗 = 0|𝑖,𝑗 ) = (1𝑗 − 𝑖,𝑗 ) 𝑃 (𝑦𝑖𝑗 = 1|𝑖,𝑗 ) = (2𝑗 − 𝑖,𝑗 ) − (1𝑗 − 𝑖,𝑗 ) ⋮ 𝑃 (𝑦𝑖,𝑗 = 𝑆|𝑖,𝑗 ) = 1 − (𝑆𝑗 − 𝑖,𝑗 ), (2) where is the standardized univariate normal distribution function and 's are estimated threshold parameters. To estimate the model parameters, we use limited-information estimation with robust weighed least square estimator which avoids demanding numerical integration in the ML estimation, and that is also robust in presence of non-normal outcome variables (B. Muthén, Du Toit, & Spisic, 1997). The models are estimated in MPlus, version 6.1 (L. K. Muthén & Muthén, 2010). 3. Results Sample exposure to traffic noise in terms of Ldvn ranged between 47 and 79dB for road-traffic noise and between 46 and 72 dB for rail traffic noise. Distributions of noise exposure in the samples exposed to road-traffic noise and rail traffic noise are displayed in figure 1. As we can see there, the rail traffic sample has been generally exposed to lower noise levels. Figure 1: Sample noise exposure (Noise) - road traffic and railway traffic 9 40 30 0 10 20 Abs. frequency 30 20 0 10 Abs. frequency 40 50 Railway (n=223) 50 Road (n=352) 40 50 60 70 80 90 40 50 Ldvn [dB] 60 70 80 90 Ldvn [dB] Average noise exposure for the two samples is further examined separately for the towns from which the samples were drawn in table 1. Results of the ANOVA tests conducted separately for road-traffic and rail traffic samples suggest that there were significant differences in exposure to noise levels between the towns. Table 1: Noise exposure (Ldvn) in samples from different towns (means, standard deviations and ANOVA) Town Praha VysokeMyto Mnisek pod Brdy Koprivnice CeskaTrebova Total ANOVA N 210 39 28 77 -354 Road traffic M 70.96 63.34 64.47 65.79 -68.48 F=52.76(3), p<0.001 SD 4.35 6.27 4.15 4.37 -5.50 N 117 ---111 228 Railway traffic M SD 59.97 3.81 ------56.04 6.14 58.06 4.45 F=34.285(1), p<0.001 An examination of table 2, which reports average noise annoyance levels in the sub-samples coming from different towns, reveals that the average reported by respondents in our sample is quite high with values of 4.13 and 3.45 for road-traffic and rail traffic annoyance respectively (where 1 stands for "not annoyed" and 5 for "extremely annoyed"). Level of annoyance seems to be similar between the different localities sampled for road-traffic annoyance and also between the localities sampled for rail traffic noise. Table 2: Average noise annoyance score in sub-samples from different towns (means, standard deviations and ANOVA test of equality) 10 Town Praha VysokeMyto Mnisek pod Brdy Koprivnice CeskaTrebova Total ANOVA N 210 39 28 77 -354 Road traffic M 4.07 4.08 4.57 4.14 -4.13 F=2.440(3), p=0.064 SD 0.91 1.04 0.92 0.93 -0.93 N 117 ---111 246 Railway traffic M 3.50 ---3.36 3.43 F=0.684(1), p=0.409 SD 1.22 ---1.25 1.23 Figure 3 displays average noise exposure for different levels of life satisfaction separately for the sample exposed to road-traffic and rail traffic noise. At first look there appears to be hardly any clear monothetic relationship, especially when we take into account the estimated confidence intervals of average noise exposure for each level of life satisfaction. 11 Figure 3: Average noise exposure for each of the life-satisfaction levels (mean and its 95% conf. int.) 65 50 55 60 Ldvn [dB] 70 75 80 Road n=7 n=9 Very dissatisfied n=4 n=25 n=22 n=82 n=33 n=60 n=64 2 3 4 5 6 7 8 n=27 n=21 9 Very satisfied Life satisfaction 65 50 55 60 Ldvn [dB] 70 75 80 Railway n=6 n=1 Very dissatisfied n=4 n=11 n=3 n=32 n=24 n=44 n=46 2 3 4 5 6 7 8 n=30 n=27 9 Very satisfied Life satisfaction The contention that the statistical relationship between noise exposure and life satisfaction is weak at best is confirmed in tables 3 and 4, which report very low and statistically insignificant correlations between noise exposure and life satisfaction in our sample and also very low correlations between noise annoyance and life satisfaction that are statistically significant (and negative as expected) only in the case of roadtraffic noise. 12 Table 3: Mans, standard deviation, and correlation between observed variables (road traffic) M 1. Ldvn 68.48 2. Sensit 2.12 3. Annoy 4.12 4. Rsat 6.44 5. Lsat 7.15 *p<.05. **p<.01. ***p<.001. SD 5.50 0.69 0.93 2.59 2.25 1 1 -.105* .142** -.132* .066 2 3 4 5 1 -.169** .029 .068 1 -.328** -.140** 1 .370** 1 Table 4: Means, standard deviation, and correlation between observed variables (railway traffic) M 1. Ldvn 58.06 2. Sensit 2.20 3. Annoy 3.45 4. Rsat 7.84 5. Lsat 8.00 *p<.05. **p<.01. ***p<.001. SD 5.44 0.84 1.22 2.17 2.27 1 1 -.095 .172** -.058 -.065 2 3 4 5 1 -.381** -.011 -.064 1 -.141* .020 1 .549** 1 Now we proceed to the estimation of the structural model for the sample of respondents exposed to roadtraffic noise and rail traffic noise. The fit of the models and structural parameter estimates are displayed in figure 4 for road-traffic noise and in figure 5 for rail-traffic noise. The fit indices for both the models suggest a very good fit of the models to the empirical data (2(3)<4.3; RMSEA<0.036; CFI>0.99). However, the fit statistics for the models with low degree of freedom, such as ours, are perhaps of a lesser theoretical importance than the estimates of structural parameters which are also displayed in figures 4 and 5. 13 Figure 4: Model estimates (road-traffic noise) Model fit .937 .986 .180** Annoy -.377*** Sensit .868 Rsatisf .020 ns .030** -.027 ns .375*** 354 32 3 4.346 0.22 0.036 0.992 .851 -.019 ns Noise N Free par. Df. 2 P-value RMSEA CFI Lsatisf Note: Arrows are used for the directed relations between constructs. β coefficients (standardized multiple regression coefficients) represent their strength. Measurement errors and unexplained proportion of variance are indicated with arrows without origin. ***p<0.001.**p<0.01.p*<0.05. ns, non-significant pvalue (p>0.05). P-values are listed for parameters in the structural model only as these are of theoretical significance. Measurement models are not represented in the path diagram. Figure 5: Model estimates (railway noise) Model fit .798 .986 .458** Annoy -.132* Sensit .979 Rsatisf .021 ns Noise .029* .106 ns .732*** -.017 ns N Free par. df. 2 P-value RMSEA CFI 228 32 3 0.409 0.938 <0.01 >0.99 .647 Lsatisf Note: Arrows are used for the directed relations between constructs. β coefficients (standardized multiple regression coefficients) represent their strength. Measurement errors and unexplained proportion of variance are indicated with arrows without origin. ***p<0.001.**p<0.01.p*<0.05. ns, non-significant pvalue (p>0.05). P-values are listed for parameters in the structural model only as these are of theoretical significance. Measurement models are not represented in the path diagram. We can observe in figures 4 and 5 that the coefficient for the path leading from residential satisfaction to life satisfaction is always positive and significant, suggesting that higher residential satisfaction leads to higher life satisfaction. On the other hand, the path from noise annoyance to residential satisfaction is 14 always significant and negative, which can be interpreted in such a way that higher noise annoyance results in decreased residential satisfaction. The path that leads from noise to noise annoyance is positive and significant in both models, indicating that exposure to higher noise levels leads likely to higher noise annoyance. Most interestingly, neither noise nor noise annoyance have any significant direct effect on life satisfaction when residential satisfaction is controlled; all their effect is mediated by this variable. This result is very similar for the two models and supports the hypothesis that residential satisfaction mediates the effect on noise exposure on life satisfaction, at least for traffic noise of similar magnitudes on which our study focused. We will return to this interesting result in more detail later in the concluding section of this paper. Continuing the examination of figures 4 and 5, we see that the path from noise sensitivity to noise annoyance is positive and statistically significant in both models. This result is quite in line with the findings of previous empirical studies, which point to the prominent role of noise sensitivity as a factor of noise annoyance (Guski, 1999; Jakovljevic et al., 2009; Job, 1999; H. Miedema & Vos, 2003; Paunović et al., 2009; Weinstein, 1978; Zimmer & Ellermeier, 1999). Noise sensitivity seems to be independent from noise levels, a result that is also in line with previous research (Schreckenberg et al., 2010). In other words, people living in a noisy area are not less sensitive to noise annoyance than people living in relatively less noisy places. This result does not support the hypothesis of the mediating role of noise sensitivity that would develop if less sensitive people move into a high-noise area and more noisesensitive people move out of these areas. Although both models fit to empirical data quite well and estimates of model parameters are generally in line with what we can learn from other studies, a closer look at the path diagrams depicted in figures 4 and 5 reveals that both models leave a sizable proportion of variance in dependent variables unexplained (computed 1-residual variance). This result is not surprising if we take into account the complexity of such phenomena as noise perception and life satisfaction and the relative simplicity of our model. As a matter of fact, noise annoyance is a product of such diverse factors as person-related variables (age, years of employment, stress score, duration of stay at the accommodation during the day), house-related variables (windows of living room and/or bedroom oriented toward the street, floor), neighbourhoodrelated variables (Leq for day and night, maximal night-time noise level, traffic flow during day and at night) (Jakovljevic et al., 2009). Also life satisfaction appears to be a phenomenon of considerable complexityand even relatively elaborate individual-level models explain only between 4 and 9% (Carroll et al., 2009), between 3 a 5%(Luechinger, 2009), between 8 and 9% (Rehdanz & Maddison, 2008) or about 9% of the variability in life satisfaction (MacKerron & Mourato, 2009). 4. Conclusions This study aimed to answer the question of whether road- and rail-traffic noise negatively affects the overall life satisfaction. Our results support the contention that traffic noise does, indeed, lower people's life satisfaction. However, the effect of noise on life satisfaction seems to be mediated by at least two other constructs, noise annoyance and residential satisfaction, which makes the detection of the link between noise exposure and quality of life non-trivial and which may also obscure the existence of this relationship. 15 The novelty of the present study consists mainly in the proposing and testing of an empirical model that links together constructs used in the study of adverse effects of noise exposure (noise annoyance, residential satisfaction) with the measure of overall life satisfaction. Previous studies dealt only with the effect of noise exposure and noise annoyance on residential satisfaction, which is only a very specific part of life satisfaction. Only one previous study dealt with the effect of one particular type of traffic noise, aircraft noise, on life satisfaction (Van Praag & Baarsma, 2005), while another study dealt with quality of life and perceived levels of traffic noise (Rehdanz & Maddison, 2008). Therefore the question whether road- and rail-traffic noise exposure also affects overall life satisfaction remained unanswered. One of the interesting finding that follows from our results is that noise annoyance mediates most of the effect of noise exposure on residential satisfaction and life satisfaction. The main adverse effect of roadand rail-traffic noise exposure (in the range of 46 and 79 dB) on the overall quality of life therefore seems to consist mainly of noise annoyance. There may be additional effects of noise exposure on residential satisfaction and/or life satisfaction unmediated by noise annoyance, but these are probably smaller than those mediated through noise annoyance and our study, which exploits two rather small samples of respondents, is probably not sensitive enough to detect these effects. This finding is quite in line with results of WHO study that quantifies noise annoyance (and sleep disturbance that some would say is closely associated with noise annoyance) as by far the largest adverse effects in terms of Disabilityadjusted life years (WHO, 2010). Of some interest is also the finding that residential satisfaction mediates most of the effect of noise exposure on the overall life satisfaction. We interpret these results as suggesting that traffic noise exposure mainly affects residential aspect of life satisfaction, at least for the type and level of noise exposure targeted in this study. This finding is in line with number of previous studies which, too, found residential satisfaction to be adversely affected by traffic noise and noise annoyance (Botteldooren et al., 2011; Kroesen et al., 2010; Schreckenberg et al., 2010). Our findings also attest to importance of the past and future research that examines effects of noise exposure and noise annoyance on residential satisfaction because residential satisfaction is, according to our study, a good indicator of those life-satisfaction aspects that are most affected by traffic noise exposure. Our study did not confirm the effect of noise exposure on noise sensitivity. Also this result seems to be in line with the literature (Schreckenberg et al., 2010). Although the cross-sectional evidence exploited in this study does not allow us to examine whether people get used to traffic noise and become insensitive, or whether noise-sensitive people have tendency to move out of noise areas, we can tell, based on our results, that noise sensitivity does not mediate the effect of noise exposure on noise annoyance, although noise sensitivity by itself affects noise annoyance. A number of limitations of the present study should be acknowledged. Firstly, our data come from a survey of a urban population exposed to rather high levels of traffic noise. This fact by itself is likely to attenuate the correlation between noise exposure (and likely also noise annoyance) on one side and life satisfaction and residential satisfaction on the other simply because the variance of noise exposure is lower than would be so in a sample of general population. However, we argue that such a bias does not compromise our general conclusions about existence of a link between traffic noise exposure and residential satisfaction. It is quite likely, on the other hand, that in different populations a direct link (undetected in this study) may exist between noise exposure and life satisfaction. 16 Another limitation of the present study lies in the fact that there is a 3 years gap between collection of noise exposure data and our survey. Our study most likely underestimated noise exposure because the traffic increased over those years (especially for the road traffic). However, from what we can learn about localities that our data come from, we are not aware on any abrupt increase in traffic flow over the three years. For this reason we believe that effects of noise exposure (but not average level of noise exposure) are not severely biased in our study. 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