Los operadores genéticos a utilizar

5.4.1 Summary

The hypotheses tested for childhood injuries in the 1946 birth cohort were the same as for the Health Survey for England (HSE). The hypotheses were only partially supported. Head injuries were significantly more common in males, but not related to socioeconomic status and family type. Behavioural characteristics such as levels of neuroticism and dare-devil activities were significantly related to head injuries, and these remained significant after adjusting for sex, socioeconomic status and family type.

Results of the childhood injury analyses in the MRC 1946 cohort study are strikingly similar to those found in the HSE 1997 analyses, even though the data were collected almost 30 years earlier, and using a different study design. The issues raised in the discussion in the previous chapter are relevant to this analysis and therefore will not be repeated, except to briefly highlight a few points.

In summary, in the analysis of the demographic, socioeconomic status, family type and behaviour/personality risk factors for childhood head and other injuries in the birth cohort, being male, from parents who separated by the age the sample child was 15 years old, and having behavioural and personality problems such as being unduly rough, dare-devil and neurotic were significant risk factors for these types of injuries. These findings were similar to those found for childhood head and other injuries in a Health Survey for England cross-sectional study (Chapter

5.4.2 Burden of injuries

In the cohort study, injuries in childhood were common, 3% had at least one head injury and more than half of the children had at least one other injury by the age of 15 years. An analysis of childhood injuries in the 1970 birth cohort study showed that between the ages of 0-5 years, 44% of children had at least one injury (Bijur et al 1988a). Between the ages of 5-10 years 42% had at least one injury. In the 1958 birth cohort study, about 23% of boys and 17% of girls experienced an injury by the age of 7 years (Power, 1992). The burden of injuries appears to be similar across the three national birth cohort studies (the 1946 MRC National Survey o f Health and Development, the 1958 National Child Development Study and the 1970 British Cohort Study).

5.4.3 Behavioural characteristics

Some of the behavioural factors were found to be significant risks for both head and other injuries independent of sex, socioeconomic status and family type. The behavioural risk factors were, as in the HSE analysis, not consistently significant

across all sexes, socioeconomic groups and family types. Bijur et al (1988b)

showed that boys who scored high for aggression at age 5 years were almost three times more likely have a hospitalised injury between the ages of 5 and 10 years. In the present study children who were aggressive and quarrelsome at age 15 years were 2% times more likely have had a head injury.

5.4.4 Sex difference

Being male was a significant risk factor for both head and other injuries, supporting the findings in the HSE study (more detail on this issue in section 6.4). The odds ratio was especially high for head injuries (2.82 [1.96-4.06]). Family type, in particular separated parents, was significantly related to other injuries, but

not to head injuries. The number of head injuries, as with a few other relationships analysed, for example, difficulties with other children, levels of energy and aggression, may not have been sufficient to test these relationships.

5.4.5 Developmental factors

An additional set of variables was assessed in the cohort study (growth and developmental factors). Some of these had a relationship with injuries in childhood. Children who weighed above 3500 grams at birth and were delayed in being able to sit without support were significantly more likely to have a head injury in childhood. However a shorter period of follow-up, for example up to five years of age, may be more appropriate to assess the relationship with developmental and growth factors. There were too few injuries in the first 5 years to allow for appropriate statistical analyses.

5.4.6 Strengths and weaknesses of study

The strengths and weaknesses o f this analysis are similar to those reported for the cross-sectional data set. As with the Health Survey for England data, the cell numbers in the stratified analyses were occasionally too low to draw any firm conclusions. This was also more obvious with the analyses assessing the clustering of risk factors, where on two occasions no children in the high risk group had at least a head injury. The temporal relationship between the risk factors and the outcome cannot be determined. An attempt was made to assess risk factors measured early in the life of the survey child. This was difficult with the behavioural measures as these were only measured later in childhood. The status of the family could not be used earlier than 15 years as few would have experienced a death o f a parent or separation of their parents. Also information on whether the child had a stepparent was not available.

The issue of missing data in cohort data is difficult to resolve, and findings may be biased when the percentage of missing data is high. Dealing with the problems of missing data was beyond the scope of this part of the analysis.

The next chapter presents the methods, results and discussion o f the childhood risk factors for adulthood head and other injuries in the MRC 1946 birth cohort study.

Chapter 6

Childhood risk factors for adulthood