Sleep disturbances in children are among the most frequent reasons for consultation in paediatric clinical practice.1,2 Previous studies report that between 25% and 46% of the paediatric population may experience some type of sleep disturbance during childhood or adolescence.3,4 The prevalence reported in the literature for children aged less than 3 years ranges between 11% and 40%.5,6 Many sleep disturbances are behavioural in nature (difficulty falling asleep, difficulty staying asleep or poor sleep hygiene),7 so their prevention and management should start as early as possible and should be pursued from the field of primary care.

Current sleep recommendations and guidelines are mainly based on expert opinion and consensus, as there is little experimental evidence in this field.2,8 Notwithstanding, the available literature evinces a growing interest in the essential link between sleep and adequate physical, cognitive and psychosocial development, including its impact on family dynamics.9–11 The sleep-onset time and the total duration of sleep in the first years of life are considered predictors for features of anxiety (separation anxiety, introversion)12,13 and have been associated with an adequate acquisition of healthy eating habits14 and increased inactivity and obesity in toddlers.15

In light of their importance, routine screening of sleep disturbances would be helpful for their early detection, which would allow appropriate intervention and thus improvement of psychosocial and cognitive outcomes in the paediatric population.16

The multidimensional nature of sleep poses challenges to its evaluation. Polysomnography and actigraphy contribute relevant data,11,17 but their usefulness is limited due to their low feasibility in large-scale population-based studies. Furthermore, they offer little towards the assessment of some behavioural factors that play important roles in sleep.1 This is why it is important to develop questionnaires that can assess subjective variables such as the restorative quality of sleep and the potential impact on the family.

The Brief Infant Sleep Questionnaire (BISQ) is one of the most widely used questionnaires currently available for the assessment of sleep in early childhood (Table 1).18 It was designed to be administered to parents of children aged 3–30 months of age. This questionnaire stands out because it is a robust instrument of proven reliability and validity, easy to use and brief (14 items), and thus could be used as a screening tool.1,7,16,19 The BISQ has been widely used in countries such as the United States and China.20–23 In addition to the English version, it has been translated to Portuguese,24 Turkish,25 Chinese21 and Nepalese.26

The Spanish primary care clinical practice guideline on sleep disorders in children and adolescents proposes this instrument as the preferred choice for screening of sleeping disorders in early childhood.27

To date, there is no version translated to Spanish and adapted to the Spanish population with an appropriate methodology, including assessment of its psychometric properties. Our hypothesis was that it would be possible to develop a Spanish version of the BISQ that would retain its good psychometric properties. Consequently, the aim of our study was to translate and adapt the original versions and analyse the reliability and validity of the new questionnaire in Spanish.

The BISQ comprises 14 items: 4 on the demographic characteristics of the child and 10 on sleep habits. There are 4 multiple-choice single-answer questions and 6 open-ended questions about the timing and duration of sleep. To adapt these items, we followed the general recommendations of the International Test Commission guidelines for test translation and adaptation28 as well as specific recommendations for adapting health-related quality of life (HRQoL) assessment tools.29,30

Once the BISQ-E questionnaire was developed through the adaptation process described above, which included the adjustment of the time frame considered “night-time” based on Spanish cultural norms and the geographical time zone, we studied its psychometric properties by assessing its validity and reliability.

Eighty-seven families with children aged 3–30 months that resided in the autonomous community of Catalonia participated in the study. The mean age of the children was 17.95 months (SD, 9.04), 59% were male, and 62% were single or first-born children. In addition, 65% were enrolled in child care. The mean age was similar in parents and mothers (36 years), and 58% of parents had a university education.

Of all the families that agreed to participate, only one withdrew from the study.

We chose the BISQ as the measure to be validated after careful consideration. To make this decision, we performed an exhaustive review of the relevant literature. Among many other studies, we identified 4 recent systematic reviews on the methods used to assess sleep in the paediatric age group.1,16,19,33 The BISQ stood out in the comparative analysis of the psychometric properties of these instruments.1,16,19Table 1 describes the different instruments designed to assess sleep mainly in early childhood that we considered for our study.

One of the main advantages of the BISQ is that it contributes to the adequate assessment of different aspects of sleep with a multidimensional approach by the use of a single and brief instrument. The different measures that are obtained with the use of the BISQ are: time of sleep onset (hours), duration of night-time sleep (hours), duration of daytime sleep (hours), total sleep duration (hours), night-time awakenings (number), duration of night-time awakenings (hours). The author of the questionnaire18 established 3 criteria to identify children with inadequate sleep patterns: a sustained pattern of more than 3 night-time awakenings, 1 hour of wakefulness during the night-time period, or total duration of sleep of less than 9h in 24h. According to Sadeh, these indicators remain stable in children between ages 6 and 30 months.18 However, given the variability of sleep patterns at these ages and the semiqualitative character of their assessment, the questionnaire cannot be used to diagnose a sleep disorder. Rather, it helps identify early and by simple means those children that could benefit from improvement of sleep habits or require further follow-up.

The BISQ has been used widely to assess the quality of sleep in the healthy paediatric population, and it has also been used to study sleep patterns in specific situations. For instance, it has been used to assess sleep in breastfed infants compared to formula-fed infants,34 in infants with Williams syndrome,35 children that snore36 and preterm infants.21 It has also been used to assess sleep in relation to obesity15 and the use of new information technologies,22 in studies on postpartum depression37 or in relation to diseases such as atopic dermatitis.38 In Spain, it has been used in a cross-sectional study that compared the populations of Asturias and Castilla y León.39

In the validity analysis, the new BISQ-E version exhibited a strong correlation with a detailed and much more labour-intensive method, the sleep diary. This suggests that the BISQ-E provides adequate measures of the dimensions assessed by the sleep diary. Furthermore, when it came to reliability, we found high test–retest correlations with values that were similar to those obtained for the original questionnaire by its author18 (Table 2). Similarly, we found an excellent agreement between the results obtained when the BISQ-E was self-administered and the results obtained when it was administered by an interviewer (questions asked by a clinician). In the sample of 60 families analysed in our study, the parents, accompanied by their children, were able to fill out the questionnaire in the waiting room of the department of paediatrics in approximately 8–10min, a fact that further reinforces that the BISQ-E could be an excellent screening tool in this population.

Among the possible limitations of the study, we ought to mention the relatively small sample size of our study, although it did suffice to obtain statistically significant values in the analysis of psychometric properties. Furthermore, the fact that all the families to which we administered the questionnaire were managed in a single centre could restrict the generalisation of our results to other populations. However, since we used the questionnaire to assess children with no detectable disease and of the ages for which the questionnaire was designed, we think that this will probably not be a relevant factor in the results that may be obtained in other populations. On the other hand, our reliability analysis had sufficient power to estimate correlations, since the correlation we assumed in the sample size calculation was much lower (0.35) than the correlations found in the study (all of which were greater than 0.5). Similarly, the analysis of validity also found strong correlations (all greater than 0.7), so our convenience sample had statistical power for the assumed estimate.

On the other hand, the retrospective assessment of sleep involves a risk of recall bias. However, this limitation is intrinsic to any type of questionnaire, and the BISQ-E has the advantage of being simpler to implement compared to other sleep assessment methods that are prospective and more objective, which makes it particularly suitable for screening at the population level. Given that the evidence in the literature demonstrates that collection of information from parents is an effective method to detect behavioural and sleep problems in children,1,19 we consider the subjective assessments of families highly relevant.

In conclusion, the results of our study allow us to assert that the BISQ-E is a valid and reliable instrument for the assessment of sleep in Spanish children. This questionnaire can be useful for screening of sleep disorders in clinical practice and in epidemiological research.

The authors have no conflicts of interest to declare.