Completness figures for locomotor disorders increased in DK, FIN, NO and SE when an increased time span was used. This for both individual diagnoses and for the locomotor complex. Overall, completeness figures were low in all four central databases, especially the completeness figures to individual diagnosis match on exact date. The completeness of individual diagnoses increased when a discrepancy of ±7 days was allowed, but only minor, or no, changes resulted when permitted discrepancy was expanded to ±30 days. In a properly functioning database system, completeness to veterinary attended cases should approach 100%, since disease events attended by a veterinarian are expected to end up as a record in the national database. Previous validation studies have suggested that we should regard overall completeness of 90% in a disease database as high, completeness of 80-89% as fair, and completeness of 70% and below as poor [16, 17]. On this basis, when allowing a ±7 days discrepancy match, completeness figures of 0.74, 0.39, 0.47 and 0.21 for veterinary attended locomotor disorder complex matches in DK, FIN, NO and SE, respectively, indicate a fair degree of completeness in DK but poor levels in the other three Nordic countries. The same applies where adjusted completeness are concerned. When comparing the validation of national databases in the Nordic region, one must remember that different classifications of completeness give rather different results. For example, while DK has a fair degree of completeness figures to locomotor complex, its completeness to individual diagnoses is as poor as that in the other three countries – suggesting that the Danish national database failed to record specific diagnoses for locomotor disorders as well as the other three countries. Further, the largest increase in matches was observed in DK when exact date match was substituted by ± 7 days discrepancy. It appears that either the disease date recordings are not exactly correct or that the Danish farmers failed to report the correct dates in FD.
Locomotor disorders often persist over a lengthy period of time , and consequently it can be argued that assessments of completeness to them should be based on a longer time period rather than the ±7 day discrepancy that was allowed in this study. Completeness figures were therefore also calculated for a ±30 day discrepancy match. FIN did not have any further matches when the ±30 day discrepancy was allowed, and in the other three countries completeness increased only minimally. The acceptable discrepancy will depend on the purpose of the database. If for example the aim is to evaluate a herd’s general welfare status, a difference in date of recording is not critical because the purpose is merely to count the number of welfare problems. If, on the other hand, the purpose was to calculate the time from an exposure to event a correct date would be important. It is important for the farmers, hoof trimmers, veterinarians and even those managing the databases to address the problem with locomotor registrations so as to obtain more reliable data in the future. Clear guidelines on what is acceptable are needed; lag days need to be clearly defined.
The number of diagnoses observed and the number of disease cases confirmed is quite different in the four countries. Completeness differs from one Nordic country to another, but the pattern of change is the same across all four countries: that is, completeness increases when date discrepancy is allowed. The national databases, especially the Danish one, have poor ability to identify the individual diagnoses obtained, since the completeness achieved are much lower than the completeness calculated for the locomotor complex as a whole. The other three countries generally have completeness figures lower than those in DK, but DK is the country with the greatest number of extra matches when locomotor diagnoses are permitted to match with any of the locomotor diagnoses within the locomotor complex. This means that the Danish database is less good than the other three national databases at correctly recording individual locomotor diagnoses, but better at detecting locomotor disorders as a whole. The main reason why completeness differs between complex- and individual diagnose level is the fact that for the complex diagnosis level, a diagnosise in the FD for the locomotor complex level could merge any of the five locomotor diagnoses in the ND. Whereas, for the individual diagnosis level, the individual diagnose recorded in FD must match the same individual diagnose recorded in the ND. Other reasons for the discrepancy between completeness for the locomotor complex and the completeness for individual diagnoses can only be speculated upon. The specification of the individual diagnostic codes in the four countries is quite distinct  and does not give an obvious explanation. In any case, it is important to set up precise criteria for the specific clinical diagnoses, whether it is ok to use locomotor complex or individual diagnoses. And it is recommended for future studies to validate the different clinical diagnosis of lameness. As the individual locomotor diagnoses have quite different aetiology, a high sensitivity and specificity of the specific diagnosis is very important. This will be necessary in future studies whether one will use the data from ND for welfare evaluations, investigations of different risk factors. For risk factors it will be necessary to look into the individual diagnoses whereas for welfare evaluations, it could be argued that it might be enough to investigate if the cow has locomotor problems or not as long as the welfare implications of the different diagnoses are believed to be the same. But still, a high validity of individual diagnosis would be a great advantage.
Adjusted FD was used due to the large amount of events that were only recorded into the ND but not into the FD. This suggests that the farmers in many cases had failed to record on the recording sheet for FD. Using the adjusted FD means that all the disease events in the ND were assumed to be correct recordings, i.e. the correctness of the ND was 100%. The use of adjusted FD is supported by validation studies for Finish  and Norwegian (Espetvedt, 2012 personal communication) national disease registers that show that the correctness is very high (>0.90) in both countries. Because the farmers failed to report all events that were in the ND it may be possible that they also failed to report all the non-veterinarian treated evens. All four countries had an increase in completeness when adjusting the sample, suggesting a poor compliance with the instructions given and thereby causing observation bias. It has been stated that inconsistency in recording patterns might cause bias and it is difficult to distinguish between herds with a truly low incidence and herds with a low level of disease reporting . To minimize the bias, lots of effort was put into informing the farmers and reminding them to record and send in their recordings.