Table 1 Methodological assessment criteria

A. Is the final sample representative of the target population? (external validity)

1. At least one of the following must apply in the study: an entire target population, randomly selected sample, or sample stated to represent the target population.

2. Response rate > 80%? If not:

a. At least one of the following: reasons for nonresponse described, non-responders described, comparison of responders and non-responders, or comparison of sample and target population.

B. Quality of the data? (internal validity)

3. Was the primary objective of the study the collection of data on musculoskeletal pain (including the shoulder) or was it taken from a survey not specifically designed for that purpose?

4. At least one of the following in the case of a questionnaire: a validated questionnaire or at least tested for reproducibility.

5. At least one of the following in the case of an interview: Interview validated, tested for reproducibility, or adequately described and standardized.

6. At least one of the following in the case of an examination: Examination validated, tested for reproducibility, or adequately described and standardized.

C. Definition of shoulder pain (SP) (internal validity)

7. Was there a precise anatomic delineation of the shoulder area or reference to an easily obtainable article that contains such specification?

8. Was there further useful specification of the definition of SP, or question(s) put to study subjects quoted such as the frequency, duration or intensity, and character of the pain. Or was there reference to an easily obtainable article that contains such specification?

9. Were recall periods clearly stated: e.g., 1 week, 1 month, or lifetime?

E. Summary

10. Item on overall quality and risk of study bias.