Introduction

The quality of life (QOL) measurement has been increasingly used as an outcome measure in clinical trials, in effectiveness studies, in health technology assessment, and in epidemiological surveys to assess the subjective health and well-being of the population [1].

In this context, the Quality of Life Group of the World Health Organization (WHOQOL group) has developed an instrument to assess QOL in a cross-cultural perspective for international use, the WHOQOL-100, composed by 100 questions [2–5]. However, the need for shorter instruments led the WHOQOL-group to develop an abridged version of WHOQOL-100, the WHOQOL-bref [3].

The increasing use of the WHOQOL-bref demands the need for normative data to be used as reference values for comparisons between groups. Normative scores from the general population provide a useful guide to interpret results in the lack of a “gold standard” in QOL measures [6].

Normative data for WHOQOL-bref are still scarce in the international literature [7, 8] and not available in Brazil. In order to fill this gap, the objectives of this study were (a) to provide WHOQOL-bref scores in a sample of a southern Brazilian general population and (b) to describe differences in mean scores according to socio-demographic characteristics of individuals.

Methodology

Sampling

The sample was planned aiming 800 individuals selected from the general population of Porto Alegre, a southern Brazilian city with 97% of the population living in urban areas, per capita GDP of approximately US$ 13,000.00 and a literacy rate of 96.7% [9].

A two-stage cluster random selection design was used. A random sample of 108 census sectors of the city was obtained, and seven households in each sector were systematically selected. All residents were invited to participate whether they met the following inclusion criteria: aged from 20 to 64 years; be literate; not having any physical or mental limitation that could prevent the reading and understanding of the instruments. The interviews were undertaken in the participants’ homes.

Instruments

WHOQOL-bref is a generic QOL instrument composed by 26 questions, two of them measuring overall and general health. The other 24 questions are divided into 4 domains: physical, psychological, social relationships, and environment. Each item scores from 1 to 5 on a Likert scale. The scores are then transformed into a linear scale between 0 and 100, with 0 being the least favorable quality of life and 100 being the most favorable one [3]. The Brazilian version of the instrument demonstrated a good performance concerning internal consistency (Cronbach′s coefficient 0.77 for domains and 0.91 for questions), discriminant validity, criterion validity, concurrent validity, and test–retest reliability (correlation coefficients ranged from 0.69 to 0.81) [5].

A questionnaire was used to obtain socioeconomic and demographic data and the presence of chronic diseases. The economic class was assessed by an index called Brazil Criterion (Critério Brasil) [10], which divides the population into economic classes. The classification and its equivalence concerning approximate mean family income in American dollars would be as follows: Class A1: Average family income of US$ 3,800; Class A2: US$ 2,300; Class B1: US$ 1,400; Class B2: US$ 800; Class C: US$ 460; Class D: US$212, and Class E: US$ 103.

Statistical analysis

Continuous data are expressed as means ± standard deviation and categorical in percentage. Comparisons of QOL mean scores among groups according to socio-demographic characteristics were performed by ANOVA, Brown-Fosythe or t test. ANOVA was used when there was homogeneity of variances and Brown-Fosythe when there was not, both of them for comparisons among two or more groups. Levene’s test was used to perform tests of homogeneity of variances. Student–Newman–Keuls (SNK) or Tamhane multiple comparison tests were used when group means differed in ANOVA. SNK was used when there was homogeneity of variances and Tamhane when there was not. For all tests, a significance level < 0.05 was established. Data were analyzed using SPSS for Windows, version 13.0 (IBM company, Chicago) and Microsoft Office Excel 2003.

Results

Study population

From 1,119 eligible individuals, 758 participated in the project, achieving a response rate of 68%. Seven exclusions were necessary, 2 for error in recording the age and other 5 (0.7%) for having more than 20% of missing data in the WHOQOL-bref questions [11]. Of the 751 subjects with data available for analysis, 703 responded to the 26 items of the instrument, leading to a completeness rate of 93%. The mean of time spent to complete the WHOQOL-bref was 8 min.

Table 1 shows the distribution of the study population compared to the general population. The lower percentage of respondents in the D economy class and the absence of participants in the E class were an expected finding, since one of the exclusion criteria of the study was illiteracy, which is generally more prevalent in these population strata. The socio-demographic characteristics of the sample are presented in Table 2.

Table 1 Socio-demographic comparison between total sample and the general population of Porto Alegre
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Table 2 Socio-demographic characteristics of the study population
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Regarding self-reported illnesses, 368 (49%) reported having some physical and/or mental disease; 103 (14%) of the interviewed said they had depression and 156 (21%) anxiety.

Quality of life

The sample means in each domain are presented in Table 3. There was a difference in the mean scores of QOL for some subgroups. Male gender presented higher values in almost all domains when compared with female gender. Regarding to age variable, post hoc tests demonstrated a significant difference between the younger individuals, who presented higher QOL scores, and the middle-aged and the older group in psychological domain. In the social domain, younger subjects presented higher QOL means when compared with middle-aged group but not compared with the older participants. At the same way, significant differences were observed among groups’ means from different economic classes. Individuals from lower classes (C and D) presented lower QOL scores when compared with individuals from A1 class. Related to years of study, the differences in means scores were observed between the lower (up to 4 years) and the higher (12 years or more) educational level groups in almost all domains. Individuals who reported to suffer from a chronic illness showed significantly lower scores than those who did not.

Table 3 Mean scores (SD) of WHOQOL-bref in the total population sample and subsamples stratified by gender, age, economic class, years of study, and presence of a chronic disease
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Table 4 shows the scores in each domain of the WHOQOL-bref in percentiles 5, 10, 25, 50, 75, 90, 95 for the total sample and for each group according to gender and age. Figure 1 shows curves for the percentiles 25, 50, and 75 of scores for men and women by age, in each domain of WHOQOL-bref.

Table 4 Percentiles of mean scores of WHOQOL-bref in the total sample and subgroups divided by sex and age
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Fig. 1
figure 1

Percentiles charts of the scores of each domain of WHOQOL-bref for men and women

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Discussion

This study provides scores of QOL measured by the WHOQOL-bref based on a sample of the general population of a southern Brazilian city. These data can be used as reference for comparison of groups of individuals in different clinical situations, as recommended by the literature that normative values obtained in the general population serve as parameter [6, 12].

The observed difference in QOL scores according to demographic variables emphasizes the need for using the standards for each subgroup for comparison purposes. Women, as well as people from lower economic classes, had worse scores in nearly all domains, as observed previously by other authors [8, 11, 13, 14]. Concerning age, the age group of 30 to 44 years had lower score means compared with those of younger, but not compared with older individuals. This finding is controversial through studies, since some authors found a QOL decrease proportional to the increase in age [8], while others have also noticed a better QOL for people above 45 years [11].

Means scores of those reported with some disease were significantly lower than healthy participants in all domains, mainly between the groups with and without self-reported depression and anxiety. This ability of WHOQOL-bref to distinguish patients with and without emotional distress had already been observed in groups of patients with chronic diseases in Brazil [15–18], and the present study highlights these findings adding information related to this property of the instrument also in the general population.

One of the caveats of this study is the fact that the sample had a subrepresentativity of the general population in relation to the lower socioeconomic classes. Some exclusion criteria such as illiteracy may have led to a smaller representation of D and E classes. Since the QOL scores decreased progressively in lower socioeconomic classes, one can infer that the classes D and E would score even lower.

The data here presented should be used with caution regarding the extrapolation of results for the country as a whole, because of heterogeneity of Brazilian population. Replication of this study in other regions could contribute to the achievement of national values.

One of the major strengths of this study for future research is to provide tables of the WHOQOL-bref scores to be used as a comparative standard for quality of life assessments in different populations. This research was undertaken according to international methodological recommendations for normatization of QOL instruments, using a random sample of the general population, describing QOL scores for different age and gender groups, and response rate over two-thirds [12].

The WHOQOL-bref proved to be a sensitive measure for socio-demographic variables, being a useful tool for identifying vulnerable groups and describing the profile of quality of life of the population.