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Sm. Sci. Med. Vol. 26, No. 8, pp. 839-843, 1988 0277-9536/88 $3.00 + 0.00 Printed in Great Britain. All rights reserved Copyr@t 0 1988 Pergamon Press plc CHILDHOOD ACCIDENTS, FAMILY SIZE AND BIRTH ORDER POLLYE. Burn,‘* JEAN GOLDING~ and MA’ITHEW KURZON’ ‘Departments of Pediatrics, Epidemiology and Social Medicine, Albert Einstein College of Medicine, 2Department of Child Health, University of Bristol, Royal Hospital for Sick Children, St Michael’s Hill, Bristol BS2 8BJ, England Abstract-The relationship between accidents and number of children in the household was assessed in 10,394 children surveyed at ages 5 and 10 years. The analyses suggest that living in a household with 3 or more children during the preschool period increases a child’s risk of experiencing accidents that result in hospitalization; and that living in a household with 4 or more children increases the risk of such accidents to school-age children. The number of older rather than younger children had the greatest impact on accident risk. The observed odds ratios suggest that children with 4 or more siblings have 80% to 90% more injuries resulting in hospitalization than only children. The proportions of children with one or more accidents (regardless of the place of treatment) and with repeat accidents were unrelated to family size. Environmental differences between families of varying size accounted for the association with hospitalized accidents. Key words-accidents, family characteristics, child, preschool The relationship between family characteristics and childhood accidents has received considerable atten- tion because of the important protective role played by the family in providing both a safe environment and a buffer between the child and the environment [l-3]. Several investigators have assessed the relationship between family size and accidents, but no consensus has emerged. In two small-scale studies, children with repeated accidents were found to come from large families more often than would be ex- pected from the overall distribution of family size or from matched controls [4,5]. In a study of almost 9000 children receiving prepaid medical care, Man- heimer et al. found that adolescents with older sib- lings had an increased risk of injuries, but that preschool children with no older siblings were at greater risk than those with one or more older siblings [6]. The overall rate of accidents in a New Zealand birth cohort of 1265 children followed to age 4 was not associated with increasing family size [7]. The use of several different measures of accidents (e.g. multiple accidents, all accidents, accidents re- sulting in hospitalization) in these studies makes comparisons between them problematic. None of the studies attempted to disentangle the effect of older siblings, younger siblings, and the stressful birth of a sibling, nor to assess if there is any effect of birth order. Finally, only one [8] used multivariate statistics to assess the interrelationships that exist between family size and other salient characteristics of fami- lies: social class, supervision, child behavior. The primary aim of this set of analyses was to assess whether there is a relationship between family size and several measures of childhood accidents in a large representative national birth cohort. A second aim was to assess whether any observed association was either due to economic and material differences *Correspondence and reprints to P. E. Bijur. 839 between families of different size, or to the stress of pregnancy and birth, or to decreasing maternal abil- ity to supervise children with increasing family size, or to varying child behavior in families of differing size. We also assessed the effect of birth order on the frequency of accidental injuries. SUBJECIS AND METHODS The data for this study were collected as part of the Child Health and Education Study which followed a birth cohort of infants at ages 5 and 10. All infants born in 1 week of April, 1970 in England, Scotland and Wales were eligible for the follow-up studies. In 1975, when the children were aged 5 years, there were 13,135 completed questionnaires: 12,732 representing 79,6% of the estimated 16,004 survivors of the cohort [9] plus 403 questionnaires from other children born in the same week, but not surveyed at birth. In 1980, when the children were aged 10, data were collected on 13,871 of the children. Extensive information is available at both time periods on the health, devel- opment and social environment of the children [lo]. Children and their families were included in this set of analyses if they had information available on accidental injuries from both the 5- and IO-year follow-up interviews, if they were singletons, if their mothers identified their own country of origin as the United Kingdom, if they were from predominantly English speaking families, if they were not in residen- tial care and if their mothers were present at the time of the 5-year interview. Of the 13,135 children inter- viewed in 1975, 1636 were excluded from these anal- yses because the interviews in which the accident questions were asked were not carried out with their mothers in 1980. There were 1105 other children excluded for not meeting one or more of the other criteria. These exclusions resulted in a sample size of 10.394.

Childhood accidents, family size and birth order

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Sm. Sci. Med. Vol. 26, No. 8, pp. 839-843, 1988 0277-9536/88 $3.00 + 0.00

Printed in Great Britain. All rights reserved Copyr@t 0 1988 Pergamon Press plc

CHILDHOOD ACCIDENTS, FAMILY SIZE AND BIRTH ORDER

POLLY E. Burn,‘* JEAN GOLDING~ and MA’ITHEW KURZON’ ‘Departments of Pediatrics, Epidemiology and Social Medicine, Albert Einstein College of Medicine, 2Department of Child Health, University of Bristol, Royal Hospital for Sick Children, St Michael’s Hill,

Bristol BS2 8BJ, England

Abstract-The relationship between accidents and number of children in the household was assessed in 10,394 children surveyed at ages 5 and 10 years. The analyses suggest that living in a household with 3 or more children during the preschool period increases a child’s risk of experiencing accidents that result in hospitalization; and that living in a household with 4 or more children increases the risk of such accidents to school-age children. The number of older rather than younger children had the greatest impact on accident risk. The observed odds ratios suggest that children with 4 or more siblings have 80% to 90% more injuries resulting in hospitalization than only children. The proportions of children with one or more accidents (regardless of the place of treatment) and with repeat accidents were unrelated to family size. Environmental differences between families of varying size accounted for the association with hospitalized accidents.

Key words-accidents, family characteristics, child, preschool

The relationship between family characteristics and childhood accidents has received considerable atten- tion because of the important protective role played by the family in providing both a safe environment and a buffer between the child and the environment [l-3]. Several investigators have assessed the relationship between family size and accidents, but no consensus has emerged. In two small-scale studies, children with repeated accidents were found to come from large families more often than would be ex- pected from the overall distribution of family size or from matched controls [4,5]. In a study of almost 9000 children receiving prepaid medical care, Man- heimer et al. found that adolescents with older sib- lings had an increased risk of injuries, but that preschool children with no older siblings were at greater risk than those with one or more older siblings [6]. The overall rate of accidents in a New Zealand birth cohort of 1265 children followed to age 4 was not associated with increasing family size [7].

The use of several different measures of accidents (e.g. multiple accidents, all accidents, accidents re- sulting in hospitalization) in these studies makes comparisons between them problematic. None of the studies attempted to disentangle the effect of older siblings, younger siblings, and the stressful birth of a sibling, nor to assess if there is any effect of birth order. Finally, only one [8] used multivariate statistics to assess the interrelationships that exist between family size and other salient characteristics of fami- lies: social class, supervision, child behavior.

The primary aim of this set of analyses was to assess whether there is a relationship between family size and several measures of childhood accidents in a large representative national birth cohort. A second aim was to assess whether any observed association was either due to economic and material differences

*Correspondence and reprints to P. E. Bijur.

839

between families of different size, or to the stress of pregnancy and birth, or to decreasing maternal abil- ity to supervise children with increasing family size, or to varying child behavior in families of differing size. We also assessed the effect of birth order on the frequency of accidental injuries.

SUBJECIS AND METHODS

The data for this study were collected as part of the Child Health and Education Study which followed a birth cohort of infants at ages 5 and 10. All infants born in 1 week of April, 1970 in England, Scotland and Wales were eligible for the follow-up studies. In 1975, when the children were aged 5 years, there were 13,135 completed questionnaires: 12,732 representing 79,6% of the estimated 16,004 survivors of the cohort [9] plus 403 questionnaires from other children born in the same week, but not surveyed at birth. In 1980, when the children were aged 10, data were collected on 13,871 of the children. Extensive information is available at both time periods on the health, devel- opment and social environment of the children [lo].

Children and their families were included in this set of analyses if they had information available on accidental injuries from both the 5- and IO-year follow-up interviews, if they were singletons, if their mothers identified their own country of origin as the United Kingdom, if they were from predominantly English speaking families, if they were not in residen- tial care and if their mothers were present at the time of the 5-year interview. Of the 13,135 children inter- viewed in 1975, 1636 were excluded from these anal- yses because the interviews in which the accident questions were asked were not carried out with their mothers in 1980. There were 1105 other children excluded for not meeting one or more of the other criteria. These exclusions resulted in a sample size of 10.394.

When the children were aged 5 years, the mothers were asked the following question:

Has (the child) ever had an accident requiring medical advice and treatment? Please include accidents in the road, home, and elsewhere, accidental ingestion of medicines/poisons, burns/scalds, eye injuries, near-drowning, bad cuts, and other injuries, with and without uncon- sciousness, and nonaccidental injuries.

At age 10, the same question was asked about accidents in the past 5 years. Three measures of accident frequency have been used: (1) the proportion of children with one or more accidents in each 5-year time period; (2) the proportion of all children with three or more accidents reported in each 5-year time period; (3) the proportion of all children with one or more accidents resulting in hospitalization in each 5-year time period.

At both time points, the children’s parents were asked to list all household members and their ages. Household members less than 16 years at the time of the survey were defined as children. At age 5 the number of births was estimated by the number of younger children in the household. At age 10 the number of births was estimated by the number of children younger than the index child at age 10 minus the number of children younger than the index child at age 5. It was assumed that the majority of other children in the household were siblings of the index child, and therefore the other children in the house- hold have been referred to as siblings in this report.

Social characteristics

At age 5, social characteristics of the families and households that were used in analyses of the data included: the 1970 Registrar general’s classification of father’s occupation [12], a measure of affluence which consists of a scale of family possessions (e.g. refrig- erator, telephone, car, television), an index of quality of the housing (e.g. type of accommodation, number of rooms, presence of garden or yard) [13], and ratings of the tidiness of the household and the quality of the furniture and possessions by the inter- viewers. For the analyses of the IO-year data the 1980 Registrar General’s classification of occupation [14], total family income, and the housing quality index were controlled analytically.

Maternal factors

Maternal characteristics that were hypothesized to affect the quality and degree of supervision of the child at age 5 included: a measure of the psycho- logical well-being of the mother, the maternal malaise inventory [15]; education of the mother; family structure--two parents, single parent with no other adults in the household, single parents with one or more other adults in the household; full and part time employment of the mother. At age 10, the maternal factors included the maternal malaise inventory, edu- cation, employment, and family structure. In analyses of the number of older children in the household and accidents, child-care provided by a sibling was also

840 POLLY E. BUUR

Child factors

At age 5 two measures of child behavior derived from the Rutter child behavior questionnaire [15] completed by the parents were used. The aggression scale includes eight descriptions of child behaviors (e.g. ‘frequently fights with other children’, ‘has tem- per tantrums’). The overactivity scale consists of three items (e.g. ‘is squirmy and fidgety’) [16]. At age 10, measures of overactivity and aggression derived by factor analysis of parent’s responses to the Rutter and Conner’s questionnaires were controlled. In ad- dition, parents reported how often the child did four activities by himself: going to shops; going to a

playground or park; playing in the street; and going on local buses.

Data analysis

The relationships between the accident measures and number of children in the household were tested by Armitage tests for linear trend [17]. The re- lationship between accidents and birth order were tested by overall xZ tests. The nominal significance criterion employed was 0.01. The relative risk as approximated by the :odds ratio was used as the measure of the magnitude of the associations.

In order to assess whether the association between family size and accidents was mediated by other family and child factors, hierarchical logistic regressions were performed first with family size entered and followed by the potential mediating variables. Reduction of the odds ratios following control of the mediators was interpreted as a measure of the mediation.

RESULTS

Total number of children and accidents

In both time periods, there were significantly higher proportions of children with one or more accidents resulting in hospitalization with increasing family size, as shown in Tables la and lb. Neither the proportion of children with one or more accidents (regardless of place of treatment) nor the proportion of children with multiple accidents was significantly related to family size. The rates of accidents resulting

Table I. Accidents by number of other children in household

controlled analytically.

Per cent with

hospital Per cent Per cent admwsion

Other with with for children (n) 31 accident > 3 accidents accident

(a) Birth to age 5 0 (1060) 44.2 2.5 5.2 I (5310) 42.8 3.7 4.8 2 (2577) 44.2 3.4 6.0 3 (935) 46.2 3.5 7.9 4+ (511) 42.3 3.5 9.0

P “.S. n.s. <O.ool

(b) Age 5-10 0 (962) 39.7 3.1 3.7 I (4885) 42.8 3.8 3.8 2 (2919) 43.2 4.0 4.6 3 (1013) 42.3 4.2 5.2 4+ (466) 41.9 4.1 6.9

P ILS. “.S. <O.Ol

Childhood accidents and family size 841

Table 2. Accidents resulting in hospitalization by number of other children in household: odds ratios (contrast PROUD - hourholds with 1 child) _ .

Number of other children in hourhold

Unadjusted O.R. 95% Cl.

Adjusted for social factors

95% C.I. Adjusted for maternal factors

95% C.I. Adjusted for child factors

95% C.I.

I 2 3 4+

(a) Birth to age 5 0.93 1.16 1.57 1.81

(0.69-1.25) (0.85-1.59) (1.10-2.25) (1.20-2.71)

0.95 I.10 I .36 I.44 (0.70-1.29) (0.80-I .52) (0.94-l .97) (0.94-2.19)

1.01 1.20 1.56 1.72 (0.74-1.37) (0.87-I .66) (1.08-2.26) (1.14-2.60)

0.94 (0.70-1.27)

I.14 (O.ESl.57)

1.50 (1.W2.16)

1.70 (l.lS2.57)

Unadjusted O.R. 95% C.I.

Adjusted for social factors

95% C.I. Ad&ted for maternal factors

95% C.I. Adjusted for child factors

95% C.I.

I .02 (0.71-1.48)

(b) Age 5-10 1.25

(0.8Sl.82)

1.05 I .25 (0.73-I .52) (0.86-1.83)

I .08 (0.7W.56)

I .30 (0.89-1.90)

1.03 (0.71-1.51)

I .22 (0.8Sl.78)

1.42 (0.92-2.20)

1.42 (0.91-2.19)

1.44 (0.93-2.23)

I.31 (0.842.03)

I.91 (1.16-3.12)

I.87 (1.14-3.06)

1.90 (l.lS3.13)

I .72 (1.04-2.83)

in hospitalization in children with one and two siblings were indistinguishable from the rates in chil- dren with no other children in the household, but those with three and four or more siblings had significantly more injuries than only children.

After controlling the set of social variables, the odds ratio contrasting the accident rates among preschool children with four or more siblings with only children was reduced by 20.0% from 1.8 1 to 1.44 which is statistically indistinguishable from an odds ratio of 1 .O (Table 2a). At age 10, control of the social variables similarly resulted in a 22.0% decrease in the odds ratio (Table 2b), which was no longer statisti- cally significant.

Control of variables related to maternal factors thought to affect the quality of child supervision (i.e. the maternal factors) resulted in a negligible change in the magnitude of the relationship between number of children in the family and hospitalized injuries in both periods. Both odds ratios contrasting those with four or more siblings with only children continued to be significantly larger than 1.0.

Adjustment for child behavior at age 5 had little effect on the size of the associations between the number of siblings and hospitalized injuries in the preschool period. In the school-age period, control of child behavior and usual child activities resulted in a

10% reduction in the magnitude of the odds ratio (contrasting four or more siblings with none), the largest reduction effected by any of the sets of explanatory variables in this age group.

Number of births, number of younger children and accidents

None of the accident measures was significantly associated with the number of births nor with the number of younger children in the household during either of the two time periods.

Number of older children and accidents

The number of older children in the family was significantly associated with the proportion of chil- dren hospitalized for accidental injuries occurring between birth and age 5 and marginally associated at age 10 (Table 3). After control of all the factors associated with supervision including childcare pro- vided by the older siblings, the risk of serious acci- dents in children with three or more older siblings was still statistically distinguishable from the risk in children with no siblings. The number of older chil- dren was not related to the proportion of children with one or more accidents nor to the proportion of children who had multiple accidents in either time period.

Table 3. Accidents resulting in hospitalization by number of older children in the household

Number of older children

0 I 2 3 4+

Birth to age 5, Age 5-10,

0’) % hospitalized (N) % hospitalized

(4104) 5.2 (4287) 4.1 (3709) 5.3 (371 I) 4.1 (1623) 6.0 (1524) 4.7 (649) 7.2 (527) 5.5 (308) 9.7 (196) 7.1

P <O.Ol to.05

842 POLLY E. BUUR

Table 4. Accidents bv birth order

Per cent

Birth order (N)

Per cent with

> I accident

Per cent with

3 3 accidents

with hospital

admission for

accident

Only child

Oldest

Middle

Youngest

P

Only child

Oldest

Middle

Youngest

P

(1060)

(3044)

( 1602)

(4687)

(962)

(3325)

( 1803)

(4155)

(a) Birth to age 5

610.4

590.0

670.4

591.2

<O.Ol

(b) Age S-10

550.9

591.9

648.4

615.4

-Co.05

2.5 5.2

3.6 5.2

4.0 7.5

3.6 5.4

n.s. < 0.01

3.1 3.7

3.7 4.2

4.8 5.7

3.9 4.2

n.s. < 0.05

Birth order and accidents

The proportion of children with one or more accidents and the proportion of children with acci- dents resulting in hospitalization were significantly higher among children who occupy a middle birth position than in children occupying other birth posi- tions (Table 4). Middle children in sibships of four or more had the highest proportion hospitalized for accidental injuries. Of the 125 children with one older sibling and two or more younger siblings at age 5, 12.0% had at least one accident resulting in hospi- talization, 2.4 times the rate in the only children.

As families with middle children have by definition at least 3 children, birth order is confounded with family size. When the analyses were restricted to families with only 3 children, occupying the middle birth order in the preschool period was marginally associated (P < 0.05) with all accidents and accidents resulting in hospitalization.

DISCUSSION

Accidents resulting in hospitalization of the child were found to be associated with the total number of other children in the household and with the number of older children, but not with the number of births or younger children. The association between serious injuries with older children in this British birth cohort parallels an association found between drownings, near-drownings and number of older siblings in Australia [18]. The authors suggested that this re- lationship may reflect the use of older children as caretakers for younger children. We found that the preschool children of working mothers who were left in the care of older children did have an increased risk of hospitalized injuries (odds ratio = 1.38), but that control of this factor and the others related to maternal supervision did not account for the ob- served association.

If inadequate supervision of children in large fam- ilies results in an increased incidence of serious accidents, we would also expect a stronger associ- ation between births and accidents, and the number of younger children and accidents, than between the number of older children and accidents, as infants and young children are more likely to stress the family’s ability to provide adequate supervision than older children. More direct measures of supervision

are needed to assess the role of this factor in the production of serious injuries.

The association between serious injuries and low social class is well-established [19,20]. In this study, the greatest adjustment (20-22%) to the magnitude of the associations between family size and accidents resulting in hospitalization in both periods came from control of social class factors thought to reflect different environmental conditions in families with varying material resources. Thus, the observed asso- ciation between the number of children in the family and accidents resulting in hospitalization may reflect the more hazardous environments of relatively disad- vantaged families. An alternative explanation is based on the suggestion that the decision to hospi- talize a child may be affected by the social conditions in the household as well as by the severity of the injury (111. Thus the apparent mediating role played by the social characteristics may reflect this bias to admit to hospital rather than increased exposure to hazardous conditions in low-income families with many children.

While child behavior problems are associated with accidental injuries [16,21-231, there is little evidence that they play a role in explaining the relationship between the total number of children in the family and hospitalized accidents.

There were no significant associations between the occurrence of one or more accidents (regardless of severity) and family size, a similar finding to several other studies [7, 191. It has been suggested that re- ports of all accidents resulting in medical attention are less reliable than reports of accidents resulting in hospitalization [24]. Thus the lack of association may be due to extraneous variability in the report of all injuries. It is also possible that there is little difference in the total frequency of accidents in families of varying size, but that those accidents that do occur in large families are more likely to result in severe injuries.

The proportion of children with three or more accidents reported in each 5-year time period was similarly unaffected by family size. This contradicts the findings from two small studies of children with repeated accidents [4,5].

There is some suggestion that middle children are at a small increased risk of experiencing accidents particularly in the preschool period.

Childhood accidents and family size 843

The source of data for accidents in this study was the children’s parents who were asked to recall medically treated injuries over the course of 5 years. While it is likely that there is considerable lack of reliability in these data, it is also likely that parents with many children would systematically under- report the accidents of the index child, while parents of only children would systematically over-report their accidents. Thus the magnitude of the observed associations may be underestimates of the true relationships.

While the thrust of public health efforts to prevent childhood accidents is the modification of the mate- rial environment [25-271, it has been suggested that pediatricians and other health workers can play a role in prevention at the individual level with high risk children [28-301. Children in large families are almost twice as likely to be hospitalized for serious injuries than children in smaller families. When this family characteristic is present in conjunction with other known risk factors such as low social class, aggressive behaviour, and male sex, health care providers should be alerted to the increased likelihood of serious accidents.

Acknowledgements-The Child Health and Education Study’s S-year follow-up was funded by a grant from the Medical Research Council, with additional support from Action for the Crippled Child and from the National Birthday Trust. The IO-year follow-up was funded by grants from the Department of Health and Social Security, the Joseph Rowntree Memorial Trust, the Department of Edu- cation and Science, the U.S. National Institute of Health and Human Development, and the Manpower Services Commission. The analyses were funded by the William T. Grant Foundation Faculty Scholars Program. We gratefully acknowledge the contribution of the Regional and District Health Authorities, Health Boards, and health visitors throughout England, Scotland and Wales and all academic staff who have previously been involved in the preparation and development of the data sets.

This research was supported by grants from the Department of Health and Social Security (U.K.), the Department of Education and Science (U.K.), the National Institute of Child Health and Human Development (U.S.A.), and the William T. Grant Foundation.

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