Author's response to reviews Title: Movement control tests of the low back; evaluation of the difference between patients with low back pain and healthy controls Authors:

Data concerning the subgroup analysis I suggested should also be presented in the abstract, This is true. We added: There was a significant difference between acute and chronic (p<0.01) as well as between subacute and chronic (p<0.03) but not between acute and subacute (p>0.7) patient groups. INTRODUCTION Page 4, para 2: by gold standard, do you mean a criterion measurement tool? This should be clarified. We added a sentence to clarify what we meant with gold standard on page 4 last sentence: By the nature of clinical instability, there is so far no gold standard for movement control of the low back. To measure the concurrent validity a test should be available which can be compared with the actually used test. This situation is frequent as gold standards are not available for many diagnostic clinical tests. Page 5, para 2: I am not convinced that the range of reliability coefficients you quote is acceptable to reliable. Would it not be more correct to infer that there is a very large range of coefficients suggesting low to high reliability. We can see your point when you include to all reliability studies done in this area. However, we are referring to our own previous study, from which we chose the 6 best tests out of 10. We chanced this sentence to: As the reliability of movement control test battery of the low back in our earlier study was shown to be acceptable to substantial for the 6 tests, the next step is to evaluate whether there is a difference in movement control between patients with low back pain and healthy controls in this test battery DATA ANALYSIS Remove “a one way ANOVA for non parametric data” as this sentence may also be interpreted that you used a 1-way ANOVA in addition to the KW test, which is not correct. We omitted “as one way ANOVA for non-parametric data”