Kosloff et al. Chiropractic & Manual Therapies (2015) 23:19
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Table 8 Odds ratio and 95% CI for association between # of exposures during 30-day hazard period Exposures All cases Age <45 yr Age >45 yr Odds ratio 95% CI Odds ratio 95% CI Odds ratio
95% CI
Commercial Any DC* visit Any PCP visit Medicare Any DC* visit Any PCP visit
1.03 2.01
0.86-1.26 1.77-2.29
1.32 2.38
0.64-2.71 1.55-3.66
1.01 1.97
0.81-1.25 1.72-2.26
0.54 1.51
0.23-1.28 1.32-1.73
*DC = Chiropractic.
While the effect of other unmeasured confounders cannot be discounted, there is reason to suspect the ab- sence of these data was not deleterious to the results. Cassidy, et al. found no significant differences in the re- sults their case-crossover design, which affords better control of unknown confounding variables, and the find- ings of their case – control study [32]. Our results highlight just how unusual VBA stroke is in the MA cohort (prevalence = 0.021%) and – even more so – for the commercial population (prevalence = 0.0032%). As a result, some limitations of this study re- lated to the rarity of reporting VBA stroke events. Des- pite the larger number of cases, data were insufficient to calculate estimates and confidence intervals for seven measures of exposure (4 commercial and 3 MA) for chiropractic visits. Additionally, we were not able to compute estimates specifically for headache and neck pain diagnoses due to small numbers. Confidence inter- vals associated with estimates tended to be wide making the results imprecise [42]. There were limitations related to the use of adminis- trative claims data. “ Disadvantages of using secondary data for research purposes include: variations in coding from hospital to hospital or from department to depart- ment, errors in coding and incomplete coding, for example in the presence of comorbidities. Random errors in coding and registration of discharge diagnoses may dilute and at- tenuate estimates of statistical association ” [43]. The recor- dings of unvalidated hospital discharge diagnostic codes for stroke have been shown to be less precise when compared to chart review [44,45] and validated patient registries
commercial and 3 million MA members. A total of 1,829 cases were identified, making this the largest case – control study to investigate the association between chiropractic manipulation and VBA stroke. Due to the nationwide setting and large sample size, our study likely reduced the risk of bias related to geographic factors. However, there was a risk of selection bias – owing to the data set being from a single health insurer – includ- ing income status, workforce participation, and links to health care providers and hospitals. Our study closely followed a methodological approach that had previously been described [32], thus allowing for more confident comparisons. The current investigation analyzed data for a number of comorbid conditions that have been identified as po- tentially modifiable risk factors for a first ischemic stroke [40]. The differences between groups were statis- tically significant for most comorbidities. Information was not obtainable about behavioural comorbid factors e.g., smoking and body mass. With the exception of hypertensive disease, there are reasons to question the clinical significance of these conditions in the occurrence of ischemic stroke due to vertebral artery dissection. A large multinational case-referent study investigated the as- sociation between vascular risk factors (history of vascular disease, hypertension, smoking, hypercholesterolemia, dia- betes mellitus, and obesity/overweight) for ischemic stroke and the occurrence of cervical artery dissection [41]. Only hypertension had a positive association (odds ratio 1.67; 95% confidence interval, 1.32 to 2.1; P <0.0001) with cer- vical artery dissection.
Table 9 Chiropractic (DC) visits with spinal manipulative treatment (SMT) Commercial Medicare DC visit with SMT Any DC visit
Total # in sample DC visit with SMT Any DC visit
Total # in sample
Stroke cases
13 47 60
19 62 81
1159 4633 5792
1
2
670
Controls
21 22
24 26
2680 3350
All
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