Table 2.
Results of hierarchical linear models for each outcome: unconditional models and models of the impact of chiropractic visit frequency
| LBP Rating (n=1361) | ODI (n=1362) | NP Rating (n=1214) | NDI (n=1213) | |||||
|---|---|---|---|---|---|---|---|---|
|
|
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| Unconditional | Adding visit frequency | Unconditional | Adding visit frequency | Unconditional | Adding visit frequency | Unconditional | Adding visit frequency | |
|
| ||||||||
| Intercept | 3.48 (0.1)*** | 3.15 (0.1)*** | 19.27 (0.4)*** | 17.10 (0.6)*** | 3.64 (0.1)*** | 3.35 (0.1)*** | 21.37 (0.4)*** | 19.57 (0.7)*** |
| Weeks Since Baseline (Weeks) | −0.03 (0.0)*** | −0.02 (0.0)** | −0.21 (0.0)*** | −0.22 (0.0)*** | −0.03 (0.0)*** | −0.02 (0.0)** | −0.23 (0.0)*** | −0.18 (0.0)*** |
| Visits to Chiropractor (Ref: Monthly to < monthly) | ||||||||
| Biweekly up to monthly | 0.25 (0.1) | 0.58 (0.8) | 0.24 (0.1) | 0.54 (0.9) | ||||
| Weekly up to biweekly | 0.60 (0.1)*** | 4.48 (0.9)*** | 0.48 (0.2)** | 3.97 (0.9)*** | ||||
| More than weekly | 0.95 (0.2)*** | 7.75 (1.1)*** | 0.72 (0.2)*** | 5.29 (1.2)*** | ||||
| Unknown | 0.41 (0.3) | 2.05 (1.6) | 0.42 (0.3) | 1.63 (1.8) | ||||
| Weeks* Biweekly to monthly | 0.00 (0.0) | 0.08 (0.0) | −0.01 (0.0) | −0.07 (0.1) | ||||
| Weeks*Weekly to biweekly | −0.01 (0.0) | 0.05 (0.1) | −0.01 (0.0) | −0.07 (0.1) | ||||
| Weeks*More than weekly | −0.05 (0.0)*** | −0.14 (0.1)* | −0.03 (0.0)* | −0.14 (0.1)* | ||||
|
| ||||||||
| Partitioned Variance | ||||||||
| Clinic (Intercept) | 0.04 (0.0) | 0.04 (0.0) | 5.26 (2.3) | 5.79 (2.3) | 0.09 (0.1) | 0.10 (0.1) | 5.23 (2.8) | 5.77 (2.9) |
| ID (Weeks) | 0.01 (0.0) | 0.01 (0.0) | 0.22 (0.0) | 0.21 (0.0) | 0.01 (0.0) | 0.01 (0.0) | 0.25 (0.0) | 0.25 (0.0) |
| ID (Intercept) | 2.51 (0.1) | 2.40 (0.1) | 122.00 (5.5) | 114.81 (5.2) | 2.82 (0.2) | 2.75 (0.2) | 127.04 (6.2) | 122.85 (6.0) |
| Residual | 1.61 (0.0) | 1.61 (0.0) | 27.75 (0.5) | 27.75 (0.5) | 1.60 (0.0) | 1.60 (0.0) | 32.67 (0.7) | 32.67 (0.7) |
|
| ||||||||
| D (df) for visits main effects | 16.2 (4) *** | 32.0 (4) *** | 7.1 (4) ** | 14.7 (4) *** | ||||
| D (df) for visits interactions | 7.5 (3) ** | 6.3 (3) ** | 2.8 (3) | 2.1 (3) | ||||
D = Deviance statistic with its degrees of freedom (number of parameters added over previous model), distributed χ2; LBP = low back pain, 0–10 scale; NDI = Neck Disability Index, 0–100 scale; NP = neck pain, 0–10 scale; ODI = Oswestry Disability Index, 0–100 scale
*
The estimated coefficient or deviance statistic is statistically significant at p<.05.
**
The estimated coefficient or deviance statistic is statistically significant at p<.01.
***
The estimated coefficient or deviance statistic is statistically significant at p<.001.