The case–control studies focused on falls, poisonings and scalds as these are among the most common types of injury resulting in hospital admission and ED attendance in children aged 0–4 years in England and the UK. In 2012/13,>26,000 children aged 0–4 years were admitted to hospital in England following
a fall, poisoning or scald,2as described in more detail below. There are no recent data available on ED
attendances, but data from 2002 show that approximately 280,000 children aged 0–4 years attended an ED following a fall, poisoning or thermal injury (burns and scalds) in the UK.3
Falls resulted in 19,569 hospital admissions in children aged 0–4 years in England in 2012/13. Of these, 18% were falls from furniture, 11% were falls down stairs or steps and 23% were falls on one level.2Falls
also result in a large number of ED attendances in the UK; in 2002, there were 229,600 attendances in children aged 0–4 years following a fall. Of these, 18% were falls down stairs or steps and 31% were falls on one level.3Falls from furniture most commonly involve beds, chairs,2,44baby walkers, bouncers,
changing tables and high chairs.45,46
Poisonings resulted in 5286 hospital admissions in children aged 0–4 years in England in 2012/3. The majority (74%) were medicinal poisonings, with 26% being non-medicinal poisonings.2Poisonings also
result in a substantial number of ED attendances in the UK; in 2002, there were 24,887 attendances in children aged 0–4 years following a poisoning.3
Scalds accounted for 1811 hospital admissions in children aged 0–4 years in England in 2012/13.2Most
(61%) were caused by drinks, food, fats and cooking oils, 13% were caused by hot tap water and 26% were caused by other hot fluids. The number of ED attendances for scalds is not routinely available, but there were 26,015 attendances for all thermal injuries in children aged 0–4 years in the UK in 2002.3
A recent UK study found that 67% of thermal injuries in children aged 0–4 years attending six hospitals in the UK and Ireland resulted from scalds;47hence, it can be estimated that approximately 17,000 ED
attendances occurred as a result of a scald in the UK in 2002.
Systematic overviews (study H)48and a systematic review and PMA (study I)49undertaken as part of the
KCS programme of research found that home safety interventions providing education, some of which also provided safety equipment, can increase safety gate use and reduce baby walker use, increase safe storage of medicines and household products and availability of poison control centre (PCC) numbers and increase the proportion of families with a safe hot tap water temperature. However, little evidence was found showing whether such interventions reduced fall-related injuries, poisonings or scalds. These reviews highlighted the lack of adequately powered RCTs of interventions to prevent falls, poisoning or scalds that measured injury outcomes. One of the challenges is that, although on a population level injuries are a major public health problem, for individual children, specific injuries are relatively rare events. Hence, trials frequently require prohibitively large sample sizes and are extremely expensive and logistically difficult. Therefore, the best available evidence for effective interventions in the field of injury prevention often comes from rigorous case–control studies, for example those for smoke alarms50and cycle helmets.51
Such evidence has had a major impact on policy and legislation. The NHS, local authorities and other organisations need to be able to make decisions about which home safety interventions to commission or provide, but at present such decisions lack an evidence base. We have therefore undertaken these case–control studies to quantify associations between modifiable risk factors and falls, poisonings and scalds in young children.
Methods
The methods for these studies are described in full in the published protocols.52–54
Objectives
The primary objectives of study A were to estimate associations between modifiable risk and protective factors and medically attended injuries resulting from five injury mechanisms in children aged<5 years:
(a) falls from furniture (b) falls on one level (c) stair falls
(d) poisoning (e) scalds.
Our secondary objectives were to explore whether or not associations between risk and protective factors and injuries varied by child age, sex, ethnicity, single parenthood, housing tenure and unemployment and injury severity.49
Study design
We used five multicentre matched case–control studies [one for each of the injury mechanisms (a)–(e)].
Setting
We recruited participants from EDs, minor injury units (MIUs) and hospital wards from acute NHS trusts in Nottingham, Bristol, Newcastle upon Tyne, Norwich, Gateshead, Derby, Great Yarmouth and Lincoln, UK. Recruitment of cases commenced on 14 June 2010 for all studies and finished on (a) 15 November 2011 for the falls from furniture study, (b) 15 November 2011 for the falls on one level study, (c) 30 September 2012 for the stair falls study, (d) 18 January 2013 for the poisoning study and (e) 18 January 2013 for the scalds study. Recruitment of controls commenced with recruitment of the first case to each study and controls were recruited within 4 months of recruitment of cases.
Participants
Cases were children aged 0–4 years with: (a) a fall from furniture
(b) a fall on one level (c) a stair fall
(d) a poisoning or suspected poisoning from a medicinal or other household product or (e) a scald, resulting in hospital admission or ED or MIU attendance.
Injuries had to have occurred at the address at which the child was registered with a general practitioner (GP) (hereafter referred to as the child’s home). Intentional and fatal injuries were excluded, as were children living in residential care. Cases were eligible to be recruited only once to the study.
We used two sources of controls; community controls and hospital controls. For clarity and simplicity the findings relating to community controls (hereafter referred to as controls) are presented in the main text of the report. Findings relating to hospital controls are summarised inAppendix 1. Children living in residential care were excluded. Controls were children aged 0–4 years without a medically attended injury of the same mechanism as the case on the date of the case’s injury. Controls were eligible to be recruited as a case or as a further control if their second recruitment occurred at least 12 months after their first recruitment. They were not eligible to be recruited more than twice to the study. We aimed to recruit an average of four controls per case, individually matched on age (within 4 months of age of case), sex and calendar time (within 4 months of case injury). To increase the study power and make the most efficient use of controls, when we recruited more than four controls per case (or when cases were later excluded), the extra controls were eligible to be matched to other cases who did not have four matched controls. These were matched on age (within 4 months of age of case), sex and calendar time (within 4 months of the case injury) and study centre, and were eligible to be used only once as an extra matched control. The eligibility of putative cases to take part in the study was assessed from medical records by clinical staff prior to study invitations being issued. Research staff also assessed eligibility on receipt of completed study questionnaires. Potentially eligible cases were approached by clinical staff face to face during their medical attendance or by telephone or post within 72 hours of their attendance. Controls were recruited by post by general practice or primary care trust (PCT) staff, from the practice register of the case’s GP or, when the case’s practice was unable to participate, from that of a neighbouring practice. To minimise age differences between cases and controls resulting from the time taken to recruit practices and then recruit controls, study invites were sent to children born up to 4 months before and 2 months after the case’s date of birth. Ten children were invited to participate for each case. One reminder was sent to case and control non-respondents 2 weeks after the original mailing.
Variables Data on injuries
We collected data from parents of cases and hospital controls on the type of injury sustained and the treatment received. We did not seek consent to access medical records to assess injury severity as we considered that this might discourage study participation. We therefore used parent-reported data on treatment as a proxy for injury severity. This is described in more detail below.
Definition of exposures
The exposures of interest were safety equipment use and home hazards measured for the 24 hours prior to the injury for cases and for the 24 hours prior to completing the questionnaire for controls. Safety behaviours were measured over the week prior to the injury for cases and the week prior to completing the questionnaire for controls.
The exposures measured for each study were:
(a) falls from furniture–use of baby walkers, playpens (or travel cots while child awake) or stationary activity centres; use of safety gates anywhere in the house; use of harnesses in high chairs; changing nappies on a raised surface; leaving child unattended on a raised surface; placing car seats or bouncing cradles on a raised surface; having objects that children could climb on to reach high surfaces;
frequency of children climbing or playing on furniture; and teaching children safety rules about falls (b) falls on one level–use of baby walkers, playpens (or travel cots while child awake) or stationary
activity centres; use of safety gates anywhere in the house; rugs/carpets firmly fixed to the floor; electric wires or cables trailing across floors; floors clear of tripping hazards; use of furniture corner covers; locking back doors to prevent access to the garden; unsupervised playing in the garden; and teaching children safety rules about falls
(c) stair falls–use of any safety gates; use of safety gates on stairs; leaving safety gate on stairs open; use of baby walkers, playpens (or travel cots while child awake) or stationary activity centres; presence of banisters and width of banister gaps; presence of handrails and tripping hazards on stairs; stairway characteristics (carpeted steps, lighting, steepness, width, landing part-way, winding stairs and steps, stair covering or handrails/banisters in need of repair); and teaching children safety rules about stairs (d) poisonings–storage of medicinal and household products (analgesics, iron/vitamins, cough medicine,
antidepressants/hypnotics and any other medicines, bleach, dishwasher products, oven cleaner, toilet cleaner, turpentine/white spirit and rat/ant killer, garden chemicals and other household products)55,56
at adult eye level or above; storage of products in locked cupboards, drawers, fridges or cabinets; frequency of returning products to usual storage place immediately after use; use of child-resistant caps (CRCs) or blister packs on products; storage of medicines in a locked medicine box; not transferring products to other containers; use of a safety gate to prevent access to the kitchen; presence of things that child may climb on to reach high surfaces; use of baby walkers; and teaching children safety rules about poisonings.
(e) Scalds–use of safety gates; presence of things that child may climb on to reach high surfaces; drinking hot drinks while holding a child; holding child while using cooker; passing hot drinks over a child; keeping hot drinks out of reach of children; use of curly/short kettle flexes; storing kettles at back of worksurface; use of back rings on cooker; turning saucepan handles away from edge of cooker; use of tablecloths; hot tap water/thermostat temperature; using cold water first when running a bath; measuring bathwater temperature; checking bath water temperature with elbow/hand; leaving child without an adult in the bath or bathroom; children running baths; frequency of child climbing or playing on furniture; use of baby walkers, playpens (or travel cots while child awake) or stationary activity centres; and teaching children safety rules about hot liquids in the kitchen and bathroom.
Definition of potential confounding variables
The potential confounding variables that were measured consisted of sociodemographic and economic characteristics, out-of-home child care and validated measures of child behaviour and temperament
[Infant Behaviour Questionnaire (IBQ),57Early Child Behaviour Questionnaire (ECBQ)58and Child Behaviour
Questionnaire (CBQ)59activity and high-intensity pleasure subscales], safety rules,60Parenting Daily Hassles
(PDH) scale (parenting tasks subscale),61,62parental mental health [Hospital Anxiety and Depression Scale
(HADS)63] and proxy-reported child
’s HRQL [PedsQL and a general health visual analogue scale (VAS)64].
Eight questions, each with three-point Likert scale responses from‘not likely’to‘very likely’, assessed perceptions of children’s ability to climb; these were analysed as a categorical variable grouping responses into (1) all not likely, (2) at least one quite likely but none very likely and (3) at least one very likely. In addition, where plausible, some of the exposures listed above were also considered as potential
confounders, for example use of a playpen may confound the relationship between use of a safety gate on stairs (as parents may be less likely to use a safety gate if they have a playpen) and the occurrence of a stair fall (as children may have less exposure to stairs if they spend time in a playpen).
As we were not able to recruit all controls from the same general practice as cases, area-level deprivation and distance from hopsital were included in all models as a priori confounders. Deprivation was measured using the 2010 version of the Index of Multiple Deprivation (IMD).65IMD scores for lower super output
areas were matched to postcode using GeoConvert.66Distance from hospital was calculated based on
postcodes and calculating straight line distances between two postcodes.67For cases we used the
postcodes of the home address and the hospital that they attended. For controls we used the postcode of the home address and that of the hospital that the matched case attended. The choice of other confounders to include in multivariable models was determined through the use of causal directed acyclic graphs (DAGs), as described inStatistical methods.
Measurement of exposures and confounding variables
We developed age-specific questionnaires (0–12 months, 13–36 months and 37–59 months) for completion by parents or guardians using previously validated measures of exposure when possible68(seeAppendix 1,
Case–control questionnaires). Questionnaires, study information leaflets and study invitation letters were pre-piloted on families from local children’s centres to assess face validity, comprehension, ease of completion and time taken to complete and were then piloted on 11 families of children who had attended EDs at participating NHS trusts and on 29 families from children’s centres in study centres.
Validation of exposure measurement (study B)
We assessed the agreement between exposures reported by parents on study questionnaires and those observed on home observations in a sample of cases and controls. Parents of participants in all case–control studies were asked to express interest in other child safety research projects (studies B, C and G) nested within study A. Home observations were undertaken as soon as possible after parents agreed to participate to miminise the time between questionnaire completion and home observation. Observations were
undertaken by trained researchers, blind to parents’responses on the study questionnaire, using a checklist of observations (seeAppendix 1, Home observation checklist for study B). To assess whether or not recent changes to the home may account for differences between reported and observed exposures, participants were asked if changes to safety behaviours, safety equipment use or home hazards had been made in the preceeding 3 months and what the changes were, if any. We chose 3 months as the time period to allow for the time taken to recruit cases and controls to the home observation study (time between receipt of questionnaire and date of home visit: median 29 days, range 1–92 days). Participants were provided with a £5 gift voucher for use in local stores to thank them for their time.
Bias
We used several strategies to try to minimise bias. We aimed to minimise recall bias by inviting cases to participate in the study within 72 hours of the injury attendance and measured exposures over a short time period prior to the injury attendance (ranging from 24 hours to 1 week); for controls we measured exposures over the same time period prior to completing the study questionnaire. When possible, we validated the accuracy of self-reported exposures in cases and controls by home observations. To minimise non-response bias, we used methods shown in systematic reviews to increase response rates, including providing a small monetary incentive (£5) for the return of completed questionnaires, using personalised
letters, sending mail by first class post, providing Freepost reply envelopes, using reminders including the provision of further questionnaires, keeping the questionnaire as short as possible and using university logos on study documentation.69,70
Study size
Validation of exposures
For a sensitivity of 80%, assuming that a minimum of 20% of participants displayed the safety behaviour, used the safety equipment or had the hazard of interest, and a CI of±20%, 80 home visits were required.
As it was plausible that sensitivity could vary between cases and controls, we aimed to recruit 80 cases and 80 controls.
Case–control studies
For the case–control studies, all sample size estimations were based on 80% power, a 5% significance level and a correlation between exposures in cases and controls of 0.1. Sample sizes were estimated to detect protective associations [i.e. an odds ratio (OR) of 0.7 for the falls studies and an OR of 0.63 for the poisoning and scalds studies]. These reductions were chosen as they were considered to be clinically important and required sample sizes that were feasible to achieve. For ease of interpretation of our results, we have presented ORs for risk factors for injury (i.e. not using safety equipment, not having a safety behaviour or having a hazard). The sample size estimations in the following sections therefore use the inverse of the protective ORs given above.
Falls
To detect an OR of 1.43, each case–control study would require 496 cases and 1984 controls for each type of fall (falls from furniture, falls on one level and stair falls), based on the exposure prevalence from previous studies71,72[not using safety gates on stairs (55%) or across doorways (70%), not using a playpen
(58%), not using a stationary activity centre (76%), rugs not firmly fixed to floors (46%), floors not clear of tripping hazards (57%%), using a baby walker (36%) and leaving a child unattended on raised surfaces (35%)]. We chose the exposure prevalence from this list that required the largest sample size.
Poisoning
To detect an OR of 1.59, 266 cases and 1064 controls would be required. This is based on the exposure prevalence estimated from the first 428 controls recruited to the study, taking account of missing data on exposures and choosing the exposure prevalence that required the largest sample size from not storing all medicines safely (27%), all cleaning products safely (55%) or all products safely (65%), not putting medicines away immediately after use (23%), not putting cleaning products away immediately after use (21%) or not putting all products away immediately after use (29%).
Scalds
To detect an OR of 1.59, 259 cases and 1036 controls would be required. This is based on the exposure prevalance estimated from the first 428 controls recruited to the study, taking account of missing data on exposures and choosing the exposure prevalence that required the largest sample size from drinking hot drinks while holding a child (27%) and not using kettles with curly/short flexes (22%).
Quantitative variables
All exposures were categorical variables. For confounders measured on a continuous scale, we assessed the linearity of their relationship with outcome measures by adding higher-order terms to regression models and tested significance using likelihood ratio tests with ap-value of<0.05 taken as significant.
When the relationship between age and the outcome of interest was non-linear we grouped age into the three age groups consistent with the age groups for which we had developed age-specific questionnaires (0–12 months, 13–36 months,≥37 months). When other relationships were non-linear, we examined distributions of the confounders and grouped values based on cut-off points that separated the distribution into groups of similar values while ensuring sufficient numbers in each group for analysis.
When standard groupings had been used in previous research, for example quintiles of deprivation scores, we grouped values similarly to allow comparisons with previous research. The cut-off points for groupings are given in the results tables.
We devised a score representing parents’perceptions of their child’s ability to climb by combining