However, this similarity needs to be interpreted with caution because of the difference in the comparators that formed the basis of the comparison, as well as difference in cost structure between countries.
Although health care costs in groups who received chiropractic care were somewhat similar across these six studies (lowest $415, highest $1,296), large differences were noted in the comparator groups (lowest $264, highest $7,904).
All observed differences in birth defects in the comparator databases could occur frequently as a result of sampling variation, coding, baseline factors, follow-up completeness, reporting years, regions, countries, environment, socioeconomic status, or lifestyle and may not represent true differences between the proportions of infants with birth defects in the comparison groups.
However, non-comparability actually follows from differences in the risk distribution in the comparators.
The reason for the non-comparability of crude event rates is usually said to be because of differences in casemix in the comparators.
Another limitation in this analysis is the differences in the cardiovascular definitions and comparators across studies.
First, significant differences in the prevalence of COPD among comparator populations might result in a modifier/confounder effect from COPD and explain why several associations were not replicated both within and across cohorts in the genome-wide association studies of lung cancer.
There were no differences in outcomes when the comparator was hydrotherapy, or when additional balancing or cycling components were included.
The model comparators were ranked from least to most costly and then incremental cost-effectiveness ratios (ICERs), representing the difference in cost divided by the difference in outcome between the comparator agents, were calculated after excluding dominated and extendedly dominated options.
