In this study, increased residential mobility in early life (before age 2
years), was associated with increased internalizing behaviour problems in children at age 9
years. The association was robust to adjustment for maternal demographic characteristics, the child’s sex, household characteristics, family experiences of stressful life events and changes in family composition. There was no effect of increased mobility after 2
years and there appeared to be no cumulative effect of number of house moves up to 9
years. These findings suggest that there is a sensitive period in early life in which increased residential mobility, even in the absence of instability in other aspects of the home environment, impacts adversely on mental health in later childhood.
In contrast with our findings, other longitudinal studies have found no independent effect of residential mobility on child behavioural development [13
]. This inconsistency may be explained by differences in the measurement of mobility. For example, Verropoulou et al. [13
] assessed whether the child had ever moved home since birth, and separately, the impact of any move associated with a change in family status. Beyers et al. [14
] measured a different construct of mobility based on the proportion of renter-occupied households and householders who had lived in the neighbourhood for less than 5
years. In this study, we quantified the number of house moves experienced by individual families and were able to examine the impact of moves at specific periods in the child’s life. As a result, our study may represent a more sensitive assessment of mobility across childhood than earlier longitudinal studies.
The mechanisms through which increased residential mobility in early life may result in the emergence of behavioural problems in later childhood are unclear. Maltreatment in infancy and early childhood has been associated with difficulties in impulse control and modulation of responses at age 4
], and trajectories of anxiety/depression and attention problems from age 4 through 10
]. The possible neuro-biological pathways linking early adversity to behavioural problems over the course of childhood have not been well-studied in humans, although brain plasticity in the early years is now well-established [24
] . Early deprivation has been studied in a range of animal species, with evidence of permanent alteration in stress regulation processes [26
Moving house is considered a stressful life event [28
]. While the causal mechanism linking mobility in early childhood to later behaviour is conjectural, we suggest that moving disrupts family routines, and can be especially stressful for all family members if the move is not voluntary. Infants from as young as 7
months have the ability to appraise situations as stressful, and from 12
months use social referencing (cues from reactions of parents and siblings) to assess events and respond emotionally or behaviourally [29
]. Therefore, young children exposed to frequent family upheaval may experience considerable stress, while not having the language skills to fully understand what is happening or to have a sense of threat alleviated. Further research investigating possible underlying causal pathways is required.
High levels of mobility can be a marker of a complex range of circumstances, including instability in other aspects of life and disadvantage, and are likely to be unevenly distributed across the population. We adjusted for a range of socioeconomic indicators, stressful events in the family, and relationship breakdown, which represents the most potent potential confounder due to it being the most common reason for a ‘non-aspirational’ house move [3
]. The association was robust to adjustment for these variables. Although we cannot rule out that the association is due to residual confounding from other unmeasured factors, these would be expected to have an at most minor influence on the observed associations [30
We did not find any association between moves linked to either an upwardly or downwardly mobile housing trajectory, and either of the outcomes, after controlling for sociodemographic factors. However, most families (78%) in this study were classified as having a housing trajectory of either continuous home ownership or rental occupancy, so there was limited statistical power to detect any effect of other trajectories on behaviour problems. Relative to continuous home ownership, continuous rental occupancy between 2 and 9
years was positively associated with externalizing behaviour; this association was attenuated but remained statistically significant after adjustment for sociodemographic factors. The reason for this association is unclear. Higher mobility has been associated with private rental tenure [32
], however in this study, the frequency of house moves was not higher in families who continuously rented than in other families. This is consistent with our lack of effect of house moves in any period on externalizing behaviour. It is possible that continuously renting may correlate with other unmeasured markers of disadvantage associated with behaviour, for example, social isolation [33
]. It is possible that our measure of housing trajectories did not capture all changes in housing tenure status across childhood. However, the number of house moves in each interval was also used in the derivation of the housing trajectories. The proportion of misclassified trajectories, and any effect on their association with child behaviour, is likely to be small. Further investigation of the common circumstances occurring in families who continuously rent is required.
The strengths of this study include the prospective measurement of housing exposures at several periods in childhood, and the application of widely used behavioural assessments with evidence of reliability and validity in this age-group [20
]. Furthermore, although directly comparable official statistics concerning house moves among families with young children are not available, data from the Australian 2007–8 Survey of Income and Housing showed that among households with dependent children (i.e. all ages), 47% had moved at least once in the previous 5
]. This is consistent with our data: in the five year interval spanning child age 5 to 9
years, 35% of study children had moved house at least once, and 60% of study children had moved at least once between birth and age 9
The study has the limitation that complete data on housing and child behaviour at the 9
year follow up were available for only 72% of the original cohort. It is possible that the most mobile families did not participate in this follow-up, as mobility is likely to affect both inclusion and ongoing participation in research. As a result, our observed effects may be conservative estimates. It is also possible that inclusion of measures of child behaviour prior to any moves could have changed the results and their interpretation, if families with children with difficult temperaments and/or later high internalizing behaviour problem scores were more likely to move. The study also has the limitation that only a low proportion of the variance in behaviour is explained by each of the models, suggesting that not all relevant factors were included.