Metodología general y consideraciones globales de implementación

Injuries, and in particular those affecting the head region, are an important public health problem. They often cause death and long-term physical and mental sequelae. However to inform the process of developing effective preventive strategies there is a need to assess the risk factors for head injuries and the medium to long-term consequences of these injuries. Preventive strategies can then be developed that have an impact on the risk factors identified from scientifically sound, population-based and generalisable research.

Most research on the risk factors of injuries relate to injuries in general rather than specific types of injuries. With head injuries being a major cause o f injury-related mortality and morbidity, its risk factors are important to assess. Studies related to head injuries often tend to focus on the immediate causes (e.g. traffic accidents, falls) rather than on the risk factors such as behavioural, socioeconomic and family factors.

Many studies assessing risk factors are cross-sectional in design, and the temporal relationship between the risk factors and the occurrence o f the head injury cannot be determined. There are few cohort studies assessing risk factors in large, population-based representative samples. Studies also do not attempt to unravel the relationship between the individual and household/environmental risk factors for head injuries.

Head injuries often have a number of short, medium and long-term consequences. These range from social, physical, cognitive to psychiatric sequelae. The consequences are mainly found in those suffering moderate to severe head injuries, while the consequences of mild head injuries are uncertain. Studies assessing the consequences o f head injuries are often not well designed; samples are small, pre-injury data are not available or analysed and the follow-up is short

(< 1 year). There are very few longitudinal studies with large population-based samples assessing the long-term effects of head injuries.

To overcome some of the shortcomings listed above, this thesis will therefore assess the risk factors for head injuries in two large, population-based samples, one a birth cohort study and the other a young people’s cross-sectional national health survey. These data sets will also allow an analysis of many risk factors, ranging from individual factors related to behaviour, to household factors, such as socioeconomic status and family type. The cohort study offers an opportunity to assess risk factors prior to the occurrence of the head injury. The cohort study will also allow an analysis of the long-term psychological and cognitive consequences (follow-up period o f more than 13 years) of childhood, adolescent and adulthood head injuries, adjusting for a few important childhood factors.

3.1 Hypotheses

Five hypotheses were tested in the study. The first two hypotheses were tested on a cross-sectional and a cohort data set. For the cross-sectional data set the temporal relationship between the risk factors and outcome cannot be determined and on the cohort data set many of the risk factors, particularly the behavioural characteristics, were measured after the occurrence of the head injury. Two further hypotheses were tested on the cohort data set, where all the risk factors were measured prior to the injury. The cohort data were used to test a hypothesis related to the long-term consequences o f head injuries.

1. Head injuries in childhood and adolescence are strongly related to being male, and living in low socioeconomic status and single or stepparent families.

2. Behavioural characteristics such as hyperactivity and conduct disorder associated with increased risk of head injuries are attenuated by sex, socioeconomic status and family type.

3. Socioeconomic status and family type in childhood, and being male, are associated with the occurrence of head injuries in young adults.

4. Behavioural characteristics such as aggression and neuroticism are associated with increased head injury risk, but the relationships are attenuated by sex, socioeconomic status and family type.

5. Children and young adults who suffer skull injuries causing concussion and skull fractures are more likely to experience long-term cognitive and psychological effects, compared to those with no or other major injuries when young.

3.2 Objectives

There are four main objectives in the study:

1. To assess the patterns o f head and other injuries in large two data sets; 1946 MRC Birth Cohort Study and the 1997 Health Survey for England,

2. to assess the relationship between sex, socioeconomic status, family type, behavioural and personality factors, and head and other injuries in children (1997 Health Survey for England and the 1946 MRC Birth Cohort Study), 3. to assess the relationship between sex, and socioeconomic status, family type

on the one hand and behavioural characteristics in childhood on the other, and head and other injuries in young adults aged 1 5 - 3 1 years in the 1946 MRC Birth Cohort Study, and

4. to assess the long-term cognitive and psychological effects in people who had skull, other and no injuries (1946 MRC Birth Cohort Study).

The next 4 chapters present the methods, results and discussions of the various data analyses carried out, starting with the risk factor analysis for childhood head and other injuries in the Health Survey for England, 1997.

Chapter 4

Risk factors for injuries in the Health