8 Summary of the methods used to develop this guidance

Introduction

The review includes full details of the methods used to select the evidence (including search strategies), assess its quality and summarise it.

The minutes of the Public Health Interventions Advisory Committee (PHIAC) meetings provide further detail about the Committee's interpretation of the evidence and development of recommendations.

All supporting documents are listed in About this guidance.

Referral

The referral received from the Department of Health on 6 July 2011 stated the need for guidance on:

'Assessing BMI and waist circumference in adults in BME groups in the UK (in relation to the risk of health problems)'.

Usually the Public Health Interventions Advisory Committee (PHIAC) examines public health interventions to see which are effective and cost effective in terms of improving a particular health condition or outcome, such as obesity.

This referral, however, was about determining whether there may be a need to intervene with some groups at lower thresholds than is usual practice for the general population. The aim was to ensure prevention advice and guidance is given to everyone at the point when they face the same level of risk.

Stages involved

The stages involved in developing this guidance are outlined in the box below.

1. Draft scope released for consultation

2. Stakeholder comments used to revise the scope

3. Final scope and responses to comments published on website

4. Evidence review undertaken and submitted to PHIAC

5. PHIAC produces draft guidance

6. Draft guidance (and evidence) released for consultation

7. PHIAC amends guidance

8. Final guidance published on website

Determining the scope and finding the evidence

This is not a typical referral, so the usual searches and appraisal of studies of effectiveness and cost effectiveness were not appropriate.

The referral itself was broad, in terms of aiming to address the 'risk of health problems' relating to health conditions associated with BMI and waist circumference in the populations of interest.

Following consultation on the scope, the CPHE project team honed the research questions and developed criteria for sifting the literature in terms of:

  • the black, Asian and other minority ethnic groups of interest in the UK

  • health outcomes of particular importance to these groups

  • study, analysis type and questions to answer the referral

  • understanding the breadth and depth of evidence available

  • summarising the search and obtaining confirmation of its completeness.

Diabetes, stroke and myocardial infarction were considered the most important conditions related to obesity and, where relevant, were most likely to have study data available. Other measures of adiposity (that is, waist to hip and waist to height ratio) were also suggested during public consultation on the scope. However, a decision was made to focus only on the 2 measures described in the DH referral.

It was decided that the focus should be on South Asian, Chinese, black, Middle Eastern and mixed-ethnicity populations worldwide, based on the prevalence of these groups within the UK. Studies of Japanese, Aboriginal and Hispanic populations were thus excluded.

Questions

Question 1: How accurate are body mass index (BMI) and waist circumference in predicting the future risk of type 2 diabetes, fatal/non-fatal myocardiaI infarction or stroke and overall mortality among adults from black, Asian and other minority ethnic groups living in the UK, compared to the white or general UK population?

Question 2: What are the BMI and waist circumference cut-off points indicating a healthy range for these measures among adults from different black, Asian and other minority ethnic groups living in the UK?

Question 3: What are the BMI and waist circumference cut-off points that indicate an increased risk of type 2 diabetes, fatal/non-fatal myocardial infarction and stroke and the need for preventive action among adults from different black, Asian and other minority ethnic groups living in the UK?

Question 4: What are the cut-off points for BMI and waist circumference among adults from black, Asian and other minority ethnic groups living in the UK that are 'risk equivalent' to the current thresholds set for white European populations?

Developing the evidence base

Identifying evidence and selection criteria

A trial search of standard literature databases conducted by the Centre for Public Health Excellence project team at NICE yielded a high volume of results (approximately12,000), many of which were irrelevant.

A Google scholar 'cited by' search was then conducted using 46 key papers identified by a small number of topic experts and the project team. This produced approximately 4000 results. These were sifted by a CPHE analyst using selection criteria developed following the expert panel meeting.

An external contractor, Bazian, used the identified literature to answer the 4 questions in the final scope.

Following this, PHIAC decided that only evidence relating to question 4 would be required to answer the DH referral. As a result, only evidence relating to question 4 has been considered during development of the draft recommendations.

Quality appraisal

Included papers were assessed for methodological rigour and quality using modified quality assessment checklists based on the tools from appendices G and J of the 'Methods for the development of NICE public health guidance', and appendices G and J of 'The guidelines manual 2009'.

Each study was graded (++, +, –) to reflect the risk of potential bias arising from its design and execution.

Study quality

++ All or most of the checklist criteria have been fulfilled. Where they have not been fulfilled, the conclusions are very unlikely to alter.

+ Some of the checklist criteria have been fulfilled. Those criteria that have not been fulfilled or not adequately described are unlikely to alter the conclusions.

− Few or no checklist criteria have been fulfilled. The conclusions of the study are likely or very likely to alter.

Given the nature of the review questions and the various settings identified and additional applicability summary score was given. This score rated how well the study results could apply to black, Asian and minority ethnic populations in the UK. It was reported using the same (++) strong, (+) moderate and (−) weak scoring system as the quality summary score. Scores are presented as quality/applicability.

Overall, if a study was rated as having a moderate summary validity score and a weak summary applicability score the following would appear in parentheses (+/−).

Summarising the evidence and making evidence statements

The review data was summarised in evidence tables (see full review).

The findings from the review and expert reports were synthesised and used as the basis for a number of evidence statements relating to each question. The evidence statements were prepared by the external contractors (see About this guidance). The statements reflect their judgement of the strength (quality, quantity and consistency) of evidence and its applicability to the populations and settings in the scope.

Secondary analysis

A team from the Department of Health Sciences at the University of Leicester and a team from The Medical Research Council (MRC) Epidemiology Unit were asked to undertake secondary analysis of UK data they possess. (The MRC worked in collaboration with the Metabolic Medicine Group at the University of Glasgow and Imperial College.) The aim was to prepare reports to answer the following question:

  • What are the cut-off points for body mass index (BMI) and waist circumference among adults from black, Asian and other minority ethnic groups living in the UK that are 'risk equivalent' to the current thresholds set for white European populations?

University of Leicester undertook an analysis of the ADDITION-Leicester Study data. This is a population-based, cross-sectional screening study of white (n=4599), South Asian (n=1310) and black (n=109) participants aged between 40 and 75 years.

The MRC unit undertook an analysis of the Southall and Brent Re-Visited (SABRE) study data. This is a population-based cohort of 4857 white European, South Asian, black African and African-Caribbean populations from north and west London. At baseline (1988–91), 4202 were non-diabetic.

How PHIAC made its decisions

At its meetings in October 2012 and March 2013, the Public Health Interventions Advisory Committee (PHIAC)/ considered the evidence and expert reports to determine:

  • whether there was sufficient evidence (in terms of strength and applicability) to form a judgement

  • whether the evidence is applicable to the target groups and context covered by the guidance.

PHIAC developed recommendations through informal consensus, based on the following criteria:

  • Strength (type, quality, quantity and consistency) of the evidence.

  • The applicability of the evidence to the populations/settings referred to in the scope.

  • Effect size and potential impact on the target population's health.

  • Impact on inequalities in health between different groups of the population.

  • Equality and diversity legislation.

  • Ethical issues and social value judgements.

  • Balance of harms and benefits.

  • Ease of implementation and any anticipated changes in practice.

  • National Institute for Health and Care Excellence (NICE)