Jensen 2015.

Study characteristics
Methods	Study design: interrupted time series (ITS) complying with the EPOC (EPOC 2009; EPOC 2013) criteria: i.e. at least three time points before and after the intervention; a clearly identified intervention point; accounting of a possible time trend and possible seasonal effects; and accounting for possible autocorrelation. The precise model specification is a linear almost ideal demand system (LAIDS), using three stage least square with fixed effects with regards to stores and defining season dummies for each month (Wooldridge 2007). Study location/setting: Denmark Timing: retrospective Allocation to group: not applicable (study without control group) Number of individuals: sales data from a balanced panel of 1293 supermarkets Database: Coop Danmark (Danish food retailer with 40% market share) Year of study: 2015 Duration of the study: 1 January 2010 to 31 October 2012 (148 weeks) Pre‐intervention: 1 January 2010 to 30 September 2011 (91 weeks) Intervention: 1 October 2011 (57 weeks until end of study duration) Unit of analysis: supermarket level
Participants	Study population: Coop Denmark supermarkets Country: Denmark Age: all ages Sex: all sexes Socioeconomic characteristics: different socioeconomic groups Eligibility criteria: not applicable Inclusion criteria: all Danish supermarkets that belong to a sales co‐operative Recruitment: no information given Equity considerations: not applicable
Interventions	Intervention: Danish tax on saturated fat covering food items with more than 2.3% saturated fat (e.g. not covering regular drinking milk or yoghurts). The tax level was set at DKK 16 (approximately USD 2.90) for each kilogram of saturated fat.
Outcomes	Primary Outcome Consumption: monthly changes in per cent of total purchased saturated fat based on the average fat content of different food products (for minced beef, regular cream, sour cream) Secondary Outcome Substitution: monthly changes in percent of total purchased food products, which are rich in fats (i.e. minced beef, regular cream, sour cream)
Notes	We contacted the corresponding author to request details concerning clarifications and additional data (e.g. sample size, measures of statistical precision), however, the author was not in position to provide this data. Funding sources: the authors reported that the project was part of a large research centre ‘UNIK – Food, Pharma, Fitness’ at the University of Copenhagen. The centre has obtained financial support from the Danish Ministry of Science. Conflict of Interest: the authors declare that they have no competing interests.
Risk of bias
Bias	Authors' judgement	Support for judgement
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Although the intervention was not blinded, participants were not aware that their data were used to investigate the effect of the tax.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Although the intervention was not blinded, participants were not aware that their data were used to investigate the effect of the tax.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	The authors did report on the completeness of their outcome data.
Selective reporting (reporting bias)	Unclear risk	The study had no published study protocol. The outcomes described in the methods section were reported, however, data were derived from databases that are permanent, commercial data collections for the purpose of market research potentially covering a wide range of products. Additionally, the study included certain food types, without providing a clear rationale for selecting particular food products.
Intervention independent of other changes (ITS)	Low risk	The intervention was a legislative act that did not have health outcomes as a motivation. No cointerventions were reported.
Shape of effect pre‐specified (ITS)	Low risk	Shape of the effect of the intervention was prespecified.
Intervention unlikely to affect data collection (ITS)	Low risk	Sources and methods of data collection were the same before and after the intervention: sales data collected through supermarket electronic cashier.
Other bias	Low risk	We did not identify other sources of bias.

EPHPP: Effective Public Health Practice Project