Hi Johny,

In general, if a survey has repeatable findings, it is reliable and if a survey is a meaningful measure, it is valid. The reliability and validity of a survey are tested empirically and then reported (i.e., psychometric evaluation).  

Surveys may undergo testing to determine 1) how well they measure the construct they are intended to measure (construct validity), 2) whether a survey reflects a certain set of abilities.(criterion validity), 3) how comprehensively it measures a construct (content validity), 4) how repeatable the findings are across raters (inter-rater reliability), 5) how well a survey consistently measures varying constructs (internal consistency reliability), and 6) how repeatable the findings are across time when administered by the same rater (intra-rater or test-retest reliability).

Hope this helps.

A couple of valuable resources for researching the psychometrics of musculoskeletal questionnaires are below. Depending on your research question and population of interest, It may be that the Nordic Questionnaire will be of use for you.

http://www.rehabmeasures.org/default.aspx

http://ergo.human.cornell.edu/cutools.html

http://occmed.oxfordjournals.org/content/57/4/300.full