Unique methodological challenges to incorporating studies on food taxation into Cochrane Reviews: comparing Cochrane EPOC and Reeves et al 2017 study design classifications




Poster session 1


Sunday 16 September 2018 - 12:30 to 14:00

All authors in correct order:

Heise TL1, Griebler U2, Katikireddi SV3, Gartlehner G2, Fenton C4, Sommer I2, Pfinder M5, Lhachimi SK1
1 Institute for Public Health and Nursing Research (IPP), Health Sciences Bremen, University of Bremen and Research Group for Evidence-Based Public Health, Leibniz Institute for Prevention Research and Epidemiology (BIPS), Bremen, Germany
2 Department for Evidence-based Medicine and Clinical Epidemiology, Danube University, Krems, Austria
3 MRC/CSO Social and Public Health Sciences Unit, University of Glasgow, Glasgow, UK
4 Usher Institute of Population Health Sciences and Informatics, Edinburgh Medical School, Edinburgh, UK
5 Department of General Practice and Health Services Research, Heidelberg University Hospital, Heidelberg, Germany
Presenting author and contact person

Presenting author:

Thomas L Heise

Contact person:

Abstract text
The World Health Organization (WHO) recommends fiscal measures (e.g. taxation of certain food items/groups) to prevent non-communicable diseases. Some primary studies assess taxation effects on food consumption patterns or sales data in real-world scenarios, but they face challenges such as seasonality of consumption patterns, substitution with other food items or sales/consumption data of different individuals before/after the implementation. Study designs investigating these effects may be common in econometrics and the social sciences, but they are uncommon in epidemiology and clinical medicine, and are rarely included in Cochrane Reviews. The current public debate on implementing food taxes does not sufficiently consider whether causality can be inferred from such study designs. At the same time, terms used for these uncommon study designs by study authors or the Cochrane Effective Practice and Organisation of Care (EPOC) study design terminology may fall short of differentiating important design features and their implications for quality of evidence.

The primary goal of this methodological case study is to compare the performance of two different study design classification systems in a sample of Cochrane Reviews: 1) the EPOC study design classification and 2) the Reeves et al 2017 classification - a taxonomy without labels.

Our case study will be based on included studies from three ongoing Cochrane Reviews on food taxation - namely the taxation of sugar-sweetened beverages, sugar and fat. Studies were detected through searches of 20 electronic databases.

We will present the major methodological advantages and shortcomings of both classification systems based on the studies included in our upcoming Cochrane Reviews on food taxation.

Public discussion on food tax implementation is substantially informed by evidence based on primary studies with uncommon types of study designs. Thus, these uncommon study designs need to be classified (and assessed) correctly by Cochrane authors. This case study of classifying primary studies according to two different classification systems will illustrate which major study design aspects are worth noting to understand how the results of individual studies can be interpreted by end-users in a meaningful way and will show room for improvement for study design classification systems in general.

Relevance to patients and consumers: 

Overconsumption of free sugars and fat are major contributors to the global burden of non-communicable diseases. Food taxation is a large scale public health intervention that may result in healthier diets at population level. However, food taxation might also have negative economic impacts, e.g. for low income groups. Evidence on the effectiveness of food taxes for improving health often includes studies of uncommon designs. Understanding the potential and limitations of uncommon study designs is crucial to foster the debate on food taxation and how such studies need to be incorporated in Cochrane Reviews.