Table 2. Differences in Differential Changes in Direct Medical Expenses and Medical Utilizations between the THA (Case Group) and Matched HA Cohorts (Control Group) before and after Time Zero.
| Direct medical expenses of the episode | Ratio | 95% CI | p-value | ||
|---|---|---|---|---|---|
| Indication of predicted graph* | Baseline medical expense mean difference (USD)† | 201.543 | 155.393–261.400 | < 0.001 | |
| Ratio of baseline direct medical expense difference | 0.975 | 0.833–1.142 | 0.757 | ||
| Ratio of direct medical expense increase per quarter | 1.014 | 1.006–1.022 | 0.001 | ||
| Ratio of difference in the slope of direct medical expense increase‡ | 1.001 | 0.990–1.012 | 0.855 | ||
| Difference in difference estimate§ | 1–6 mo | 1.069 | 0.969–1.179 | 0.184 | |
| 7–12 mo | 0.822 | 0.734–0.944 | 0.004 | ||
| 13–18 mo | 0.855 | 0.750–0.999 | 0.049 | ||
| 19–24 mo | 0.835 | 0.707–0.987 | 0.034 | ||
| 25–30 mo | 0.863 | 0.716–1.041 | 0.124 | ||
| 31–36 mo | 0.894 | 0.724–1.105 | 0.300 | ||
| Hospital LOS | |||||
| Indication of predicted graph* | Baseline LOS mean difference (day)† | 0.143 | 0.096–0.214 | < 0.001 | |
| Ratio of baseline LOS difference | 0.756 | 0.568–1.007 | 0.056 | ||
| Ratio of LOS increase per month | 0.986 | 0.973–1.000 | 0.045 | ||
| Ratio of difference in the slope of the LOS increase‡ | 1.012 | 0.993–1.030 | 0.224 | ||
| Difference in difference estimate§ | 1–6 mo | 0.969 | 0.811–1.157 | 0.728 | |
| 7–12 mo | 0.799 | 0.651–0.981 | 0.032 | ||
| 13–18 mo | 0.761 | 0.603–0.960 | 0.021 | ||
| 19–24 mo | 0.750 | 0.574–0.977 | 0.034 | ||
| 25–30 mo | 0.762 | 0.563–1.032 | 0.079 | ||
| 31–36 mo | 0.781 | 0.558–1.094 | 0.150 | ||
| Number of outpatient visits | |||||
| Indication of predicted graph* | Baseline number of outpatient visits mean difference (number)† | 14.323 | 12.451–16.477 | < 0.001 | |
| Ratio of baseline number of outpatient visits difference | 1.039 | 0.961–1.124 | 0.334 | ||
| Ratio of number of outpatient visits increase per month | 1.003 | 0.999–1.007 | 0.164 | ||
| Ratio of difference in the slope of the number of outpatient visits increase‡ | 0.998 | 0.993–1.004 | 0.538 | ||
| Difference in difference estimate§ | 1–6 mo | 1.024 | 0.972–1.078 | 0.380 | |
| 7–12 mo | 1.035 | 0.976–1.097 | 0.249 | ||
| 13–18 mo | 1.049 | 0.981–1.122 | 0.161 | ||
| 19–24 mo | 1.013 | 0.936–1.096 | 0.745 | ||
| 25–30 mo | 1.009 | 0.923–1.103 | 0.840 | ||
| 31–36 mo | 1.001 | 0.904–1.107 | 0.979 | ||
THA: total hip arthroplasty, HA: hemiarthroplasty, CI: confidence interval, USD: U.S. dollar, LOS: length of stay.
*Indication of the predicted graph: indicators of the predicted graph for direct medical expenses considering the increase in direct medical expenses of both groups before matching. †Baseline medical expense difference: difference in direct medical expense, length of stay, and number of outpatient visits between THA and HA group at 3 years before time zero. ‡Slope difference: difference in the slope of the increase in direct medical expenses, length of stay, and number of outpatient visits in the patients with THA and HA. §Difference in difference estimate: the ratios of direct medical expenses, length of stay, and number of outpatient visits at each time point, considering the difference in direct medical expenses, length of stay, and number of outpatient visits before and after time zero in the THA group and the difference in direct medical expenses, length of stay, and number of outpatient visits before and after time zero in the HA group.