Grey literature includes a range of documents not controlled by commercial publishing organisations. This means that grey literature can be difficult to search and retrieve for evidence synthesis. Much knowledge and evidence in public health, and other fields, accumulates from innovation in practice. This knowledge may not even be of sufficient formality to meet the definition of grey literature. We term this knowledge ‘grey information’. Grey information may be even harder to search for and retrieve than grey literature. On three previous occasions, we have attempted to systematically search for and synthesise public health grey literature and information—both to summarise the extent and nature of particular classes of interventions and to synthesise results of evaluations. Here, we briefly describe these three ‘case studies’ but focus on our post hoc critical reflections on searching for and synthesising grey literature and information garnered from our experiences of these case studies. We believe these reflections will be useful to future researchers working in this area. Issues discussed include search methods, searching efficiency, replicability of searches, data management, data extraction, assessing study ‘quality’, data synthesis, time and resources, and differentiating evidence synthesis from primary research. Information on applied public health research questions relating to the nature and range of public health interventions, as well as many evaluations of these interventions, may be predominantly, or only, held in grey literature and grey information. Evidence syntheses on these topics need, therefore, to embrace grey literature and information. Many typical systematic review methods for searching, appraising, managing, and synthesising the evidence base can be adapted for use with grey literature and information. Evidence synthesisers should carefully consider the opportunities and problems offered by including grey literature and information. Enhanced incentives for accurate recording and further methodological developments in retrieval will facilitate future syntheses of grey literature and information.

Financial incentive interventions have been suggested as one method of promoting healthy behaviour change. To conduct a systematic review of the effectiveness of financial incentive interventions for encouraging healthy behaviour change; to explore whether effects vary according to the type of behaviour incentivised, post-intervention follow-up time, or incentive value. Searches were of relevant electronic databases, research registers, www.google.com, and the reference lists of previous reviews; and requests for information sent to relevant mailing lists. Controlled evaluations of the effectiveness of financial incentive interventions, compared to no intervention or usual care, to encourage healthy behaviour change, in non-clinical adult populations, living in high-income countries, were included. The Cochrane Risk of Bias tool was used to assess all included studies. Meta-analysis was used to explore the effect of financial incentive interventions within groups of similar behaviours and overall. Meta-regression was used to determine if effect varied according to post-intervention follow up time, or incentive value. Seventeen papers reporting on 16 studies on smoking cessation (n = 10), attendance for vaccination or screening (n = 5), and physical activity (n = 1) were included. In meta-analyses, the average effect of incentive interventions was greater than control for short-term (≤six months) smoking cessation (relative risk (95% confidence intervals): 2.48 (1.77 to 3.46); long-term (>six months) smoking cessation (1.50 (1.05 to 2.14)); attendance for vaccination or screening (1.92 (1.46 to 2.53)); and for all behaviours combined (1.62 (1.38 to 1.91)). There was not convincing evidence that effects were different between different groups of behaviours. Meta-regression found some, limited, evidence that effect sizes decreased as post-intervention follow-up period and incentive value increased. However, the latter effect may be confounded by the former. The available evidence suggests that financial incentive interventions are more effective than usual care or no intervention for encouraging healthy behaviour change. PROSPERO CRD42012002393

Jean Adams and colleagues argue that population interventions that require individuals to use a low level of agency to benefit are likely to be most effective and most equitable.

Reported associations between preparing and eating home cooked food, and both diet and health, are inconsistent. Most previous research has focused on preparing, rather than eating, home cooked food; used small, non-population based samples; and studied markers of nutrient intake, rather than overall diet quality or health. We aimed to assess whether frequency of consuming home cooked meals was cross-sectionally associated with diet quality and cardio-metabolic health. We used baseline data from a United Kingdom population-based cohort study of adults aged 29 to 64 years (n = 11,396). Participants self-reported frequency of consuming home cooked main meals. Diet quality was assessed using the Mediterranean Diet Score, Dietary Approaches to Stop Hypertension (DASH) score, fruit and vegetable intake calculated from a 130-item food frequency questionnaire, and plasma vitamin C. Markers of cardio-metabolic health were researcher-measured body mass index (BMI), percentage body fat, haemoglobin A1c (HbA1c), cholesterol and hypertension. Differences across the three exposure categories were assessed using linear regression (diet variables) and logistic regression (health variables). Eating home cooked meals more frequently was associated with greater adherence to DASH and Mediterranean diets, greater fruit and vegetable intakes and higher plasma vitamin C, in adjusted models. Those eating home cooked meals more than five times, compared with less than three times per week, consumed 62.3 g more fruit (99% CI 43.2 to 81.5) and 97.8 g more vegetables (99% CI 84.4 to 111.2) daily. More frequent consumption of home cooked meals was associated with greater likelihood of having normal range BMI and normal percentage body fat. Associations with HbA1c, cholesterol and hypertension were not significant in adjusted models. Those consuming home cooked meals more than five times, compared with less than three times per week, were 28% less likely to have overweight BMI (99% CI 8 to 43%), and 24% less likely to have excess percentage body fat (99% CI 5 to 40%). In a large population-based cohort study, eating home cooked meals more frequently was associated with better dietary quality and lower adiposity. Further prospective research is required to identify whether consumption of home cooked meals has causal effects on diet and health.

Many dietary interventions assume a positive influence of home cooking on diet, health and social outcomes, but evidence remains inconsistent. We aimed to systematically review health and social determinants and outcomes of home cooking. Given the absence of a widely accepted, established definition, we defined home cooking as the actions required for preparing hot or cold foods at home, including combining, mixing and often heating ingredients. Nineteen electronic databases were searched for relevant literature. Peer-reviewed studies in English were included if they focussed mainly on home cooking, and presented post 19th century observational or qualitative data on participants from high/very high human development index countries. Interventional study designs, which have previously been reviewed, were excluded. Themes were summarised using narrative synthesis. From 13,341 unique records, 38 studies - primarily cross-sectional in design - met the inclusion criteria. A conceptual model was developed, mapping determinants of home cooking to layers of influence including non-modifiable, individual, community and cultural factors. Key determinants included female gender, greater time availability and employment, close personal relationships, and culture and ethnic background. Putative outcomes were mostly at an individual level and focused on potential dietary benefits. Findings show that determinants of home cooking are more complex than simply possessing cooking skills, and that potential positive associations between cooking, diet and health require further confirmation. Current evidence is limited by reliance on cross-sectional studies and authors' conceptualisation of determinants and outcomes.