1. Feasibility study childhood Outcome Measures
Dr C Humphreys
Specialist Registrar in Public Health

2. What will we learn? Information on obesity Using approach:
What cut-off to use for BMI?
Using approach:
Likely level of participation
Likely data quality
Experiences of
Children
Staff
Parents
Unexpected problems
Costs

3. BMI in children
Lack of evidence to support specific BMI cut-offs in children (NICE, 2006)
Classification is aribtary and ‘not based on known medical risk’

4. 1990 UK Centile charts Individual children: Populations:
91st & 98th centiles (overweight/obese)
NICE (‘pragmatic’)
SIGN
Department of Health
Populations:
85th & 95th centiles (overweight/obese)
Historical use
PSA targets (England)
BMI 30, age 18
BMI 25, age 18
Source: Faculty of Public Health (2007) Lightening the Load
Reproduced with kind permission from the Faculty of Public Health and
The Child Growth Foundation Orange graphics not present in original

5. International Obesity Task Force
Age and sex specific cut offs (2-18 yrs)
Relates to BMI 30 / 25, age 18
6 countries pooled data
(Brazil, Great Britain, Hong Kong, Netherlands, Singapore, USA)
Population monitoring
Foresight
Comparability
Smooth transition
European surveillance (proposed)
High specificity (NICE)
Risks (FPH)
Possible underestimation esp. obese boys
No underweight cut-off
FPH (2007) Lightening the Load
NICE (2006) Obesity: the prevention, identification, assessment and management of overweight and obesity in adults and children, section 2

6. WHO Growth standards Released 2007; use international data;
match with WHO 0-60 month charts (2006)
Also proposed for European surveillance study
Source: World Health Organization

7. Question? What cut-off to monitor population overweight/obesity
If feeding information back to family what form should this take?
Wt / ht without BMI (as in England up to now)
BMI with interpretation – what cut off?
Supporting information?

8. Possible Study Outcomes
Response rate
Parent refusal
Child refusal
Child unavailable
Data quality
Completeness of fields
Face validity
‘impossible’ entries
Feedback, routine, prospective:
Child at time of measurement:
Assessment by staff
Verbal concern
Non-verbal distress
Self assessment (e.g. happy/sad faces for 5 year olds)
School experience on day
Any feedback from parents to school or measuring staff

9. Approaches to outcome measures
Agree on a single approach and apply uniformly
Apply different approaches and compare outcomes
Different approaches by Trust
Cluster randomize schools within Trust?
What to compare?
Opt in vs opt out consent?
Who takes the measures?

10. Numbers Primary School Secondary Other 5 yr olds* 11 yr olds*
Flintshire & Wrexham 84 12 3
3299
3474
Merthyr & Cynon** 58 10
1370
1603
Powys
109 13
1395
1692
Pembrokeshire 96 8 2
1355
1573
Total
347 43 5
7419
8342
*2005 population estimates. ONS
**Cynon population estimates calculated using a conversion factor from total RCT population. Conversion factor based on 2001 census figures (ONS)

11. Power Response rate Weight Assuming 90% base (α 0.05; β 0.8):
To detect a difference of 2% (i.e. 90 vs 92%)
2,842 total
Assuming 80% base:
To detect a difference of 5%; (i.e. 80% vs 82%)
1,890 total
To detect a difference of 2% (i.e. 80% vs 82%)
12,276
Weight
Overweight: assuming 20% base in girls; to detect a difference of 1% (α 0.1; β 0.8) 4,500.
9,000 required
Obesity assuming 5% base in boys/girls; to detect a difference of 1% (α 0.5; β 0.8) 1,830.
3,660 required
R Williams (2007)

12. Questions What are the preferred outcome measures?
Should comparisons be used?
If so, by what approach?

13. Thank you