| Inclusion criteria |
| 1. Studies quantitatively measuring the prevalence or incidence of any symptomatic gastrointestinal infection in a representative population sample |
| 2. Studies quantitatively measuring socioeconomic status at an individual or aggregate level by occupation, income, education, employment or area deprivation |
| 3. Studies reporting a quantitative association between the first two inclusion criteria i.e. reporting an association between gastrointestinal infection and socioeconomic status |
| 4. Studies written or translated into English language |
| 5. Studies reporting on human subjects |
| 6. Subjects selected from the populations of countries that are members of the Organisation for Economic Co-operation and Development (OECD), reporting data after 1980 or the date that they became a member of the OECD |
| 7. Studies reporting on data collected after 1980 |
| 8. Observational studies |
| Exclusion criteria |
| 1. Unrepresentative population sample |
| 2. Outbreak reports |
| 3. Studies analysing travel related cases only |
| 4. Review studies |
| 5. Case reports |
