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Table 6 BOLD Power Estimates (registry size = 5,000 patients)*

From: Study protocol: The back pain outcomes using longitudinal data (BOLD) registry

 

Index Case Prevalence

 

2%

3%

5%

10%

Number of Cases

100

150

250

500

Effect Size (D)

RDQ†

1.5

-

-

61%

88%

2.0

-

63%

84%

98%

2.5

65%

82%

96%

99%

Pain NRS†

0.7

-

52%

74%

96%

1.0

65%

82%

96%

99%

1.3

87%

96%

99%

99%

Incremental Cost per QALY Gain < $50,000††

$500 / 0.03 D QALY

-

-

-

38%

$500 / 0.06 D QALY

45%

61%

82%

98%

$800 / 0.03 D QALY

-

-

-

21%

$800 / 0.06 D QALY

36%

51%

72%

95%

Rare Events (Surgery, Complication, or Binary Event Rate)**

2% Incidence Rate

RR = 1.5

-

-

-

-

RR = 2.0

-

-

-

62%

RR = 2.5

-

-

60%

88%

5% Incidence Rate

RR = 1.5

-

-

-

51%

RR = 2.0

-

51%

73%

95%

RR = 2.5

-

79%

95%

99%

  1. *Comparisons where power estimates are below 50% are not provided
  2. † Conservatively assumes 1:1 case:control ratio, SD estimates of 7.5 and 3.0 for RDQ and Pain NRS respectively.
  3. †† Conservatively assumes 1:1 case to control ratio, calculated for one-year time period, cost standard deviations of $4,000 per group, QALY standard deviations of 0.2 per group based on EQ-5D and 6-month effect improvement, and a positive correlation of 0.3 between costs and changes in EQ-5D [47]. Assuming a negative correlation did not affect power substantially.
  4. **Assumes 3:1 matching of controls to index cases.