Background: Guidelines use a range of evidence to support recommendations and limitations are often placed on what evidence is relevant and applicable. Limitations are usually defined on the population, intervention, or comparators, but can also include other limitations, such as location or language.

Objectives:
• to describe the limitations applied in a national programme of public health (PH) guidance, with a focus on location and language;
• to estimate the impact of excluding evidence from low- and middle-income countries (LMIC).

Methods:
We did the following:
• identified all PH evidence reviews of effectiveness published in 2016;
• assessed whether limitations on location or language were applied, and how this was done; and,
• searched for relevant systematic reviews focused on LMIC.

Results: In 2016, 6 guidelines were published, including reviews of effectiveness. Of these
• most defined some restriction based on location in the protocol;
• most did not apply a filter to limit by location at the searching stage, but applied this at sifting and full-text stages; and,
• all reported limitation by language (English only).
At full-text stage, in total, 16 studies were reported as being excluded on location (n=12) or language (n=4). Of the minority of guidelines that did not restrict on location, in total, only 1 primary study from a LMIC was included. Where limitations were applied, most were based on OECD membership. Of the OECD member countries, only 2 (Mexico and Turkey) are not high-income countries as defined by the WHO. In total, 3 studies from LIMC were therefore included as OECD member countries. These were:
• 1 multi-site research study, including 1 site in Mexico;
• 1 research study based on the border of Mexico; and,
• 1 systematic review, including a study from Turkey.
We will also present if systematic reviews using evidence from non-OECD countries could have provided more information.

Conclusions:Systematic reviewers and guideline developers often limit evidence to named countries; this can be justified and appropriate. However, relevant evidence can be excluded and this limitation should be explicitly recognised.