Trial of Inserting Prevalence Information Into Lumbar Spine Imaging Reports: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Trial of Inserting Prevalence Information Into Lumbar Spine Imaging Reports (NCT02015455), a randomized na study. The primary outcome is Relative Value Unit (RVU) for Spine-related Interventions.

2. Clinical Question

3. Trial Design

The registry identifies this as the Lumbar Imaging With Reporting of Epidemiology pragmatic cluster randomized trial. It records randomized allocation, no masking, and a crossover model. Clinics, rather than individual patients, are described as receiving the reporting conditions. In the intervention condition, lumbar imaging reports included epidemiologic benchmarks; in usual care, clinics used typical reports without those benchmarks. The enrollment field records 250401. The trial status is completed.

A cluster design assigns groups such as clinics to conditions, rather than assigning each patient independently. This can be useful when an intervention changes a clinic-level practice, since it may be difficult to use different reporting approaches for people seen in the same clinic without the approaches influencing one another. The record does not report the number of clinics, the allocation sequence, or the details of how clusters were assigned.

The crossover designation indicates that the design involved crossover, but the record does not report when clinics changed conditions, the order of conditions, or any washout period. Those details matter when considering possible time trends or carryover from one reporting approach to another. Masking is recorded as none; the registry does not describe whether outcome assessors or analysts were masked.

The trial's stated goal was to assess whether epidemiologic information in imaging reports affected subsequent diagnostic and therapeutic interventions. The primary endpoint focused on spine-related RVUs during the 12 months after index imaging. Other registered outcomes included opioid prescriptions, cross-sectional imaging, back-pain-related estimated payer costs, spine surgery, and RVUs over a longer follow-up period. The registry records 13 outcome measures and 5 analyses, but does not provide a complete account of how each outcome was analyzed.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Of 250,401 enrolled participants, 238,886 met inclusion and exclusion criteria.

Step 0 - Oct 2013 to Mar 2014

Step 1 - Apr 2014 to Sep 2014

Step 2 - Oct 2014 to Mar 2015

Step 3 - Apr 2015 to Sep 2015

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: These are analyzed participant who met all inclusion criteria and did not have any exclusions.

6. Primary Endpoint

The registry lists the primary outcome as Relative Value Unit (RVU) for Spine-related Interventions, measured over 12 months.

The primary endpoint is median spine-related relative value units (RVUs) for the 12 months after index imaging. The measure sums the RVUs associated with inpatient and outpatient procedures in that period. Each procedure's RVU reflects the relative cost of its work and practice components; it is a measure of resource use, not a direct measure of pain, function, or clinical benefit. The registry notes that the Medicare conversion factor during the study period was approximately $35/RVU, but the endpoint itself is reported in RVUs.

A composite resource-use measure can capture several kinds of care within a single outcome. In this trial, the measure represents the intensity of back-pain interventions through the RVUs assigned to spine-related procedures. The median describes the middle of the observed distribution, rather than the arithmetic average. This can be informative when a distribution is skewed, as may occur when many observations have relatively low use and a smaller number have high use. The record specifies the median as the endpoint parameter and the inter-quartile range as its dispersion measure.

RVUs are used because the trial's question concerned subsequent care following lumbar imaging, including whether intervention use differed between reporting conditions. They do not distinguish whether a particular procedure was appropriate or beneficial, and the registry does not report patient-level clinical outcomes as the primary endpoint.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary result is a mixed models analysis of the percent difference in median spine-related RVUs. The registry reports the effect estimate, a 95% confidence interval, and a p-value. Each component answers a different statistical question: the estimate describes the result's direction and scale, the interval conveys uncertainty, and the p-value measures compatibility with a specified null model under the analysis assumptions.

Why use a mixed model?

General: Mixed models can represent the dependence among observations that share a group, such as patients treated within the same clinic. They can also account for structured sources of variation, rather than treating every observation as independent. This is relevant to cluster-randomized research because participants within a clinic may share practices or other characteristics. The registry names mixed models as the analysis method but does not report the model formula, the random or fixed effects, the covariance structure, or the covariates used.

The crossover designation adds another possible source of structure: observations may be associated with both a clinic and a period or treatment condition. General: an analysis of a crossover design may need to represent period effects and possible carryover, depending on the actual design and data. The registry does not report whether or how these considerations were included in the sponsor's model. No assumptions about the exact model specification can be made from the method label alone.

What does the median represent?

General: The median is the point that divides an ordered distribution so that observations fall on either side of it. Unlike a mean, it is not strongly affected by the magnitude of unusually high observations. That can make it useful for outcomes with skewed distributions. The inter-quartile range describes the span of the middle portion of the distribution. The registry names the median as the primary parameter and the inter-quartile range as the dispersion measure, but the reported comparison is expressed as a percent difference in median.

The primary endpoint is based on RVUs summed across inpatient and outpatient procedures during the year following index imaging. The sponsor's analysis reports a percent difference in median, not a raw RVU difference. The registry does not state how the percent difference was parameterized in the model or give further detail about how the reported medians were estimated.

How should the confidence interval be read?

General: A confidence interval communicates the uncertainty around an estimate under the assumptions of the statistical procedure. A 95% confidence interval is generated by a method designed to cover the underlying quantity in 95% of repeated applications under those assumptions. It is not a guarantee that the true value lies in a particular interval, and it does not represent the range of individual participant outcomes.

For this result, the reported 95% interval runs from -2.9 to 1.5 around the estimate of -0.7. Because its values lie on both sides of no difference, it does not identify a clearly one-directional effect. Its width is also relevant: estimates throughout the interval remain compatible with the reported data under the model. The registry does not report a clinically important threshold against which to judge that range.

What does the p-value add?

General: A p-value describes the probability, under a specified null hypothesis and statistical model, of obtaining results at least as inconsistent with that hypothesis as the results observed. It is not the probability that the null hypothesis is true, nor the probability that chance alone caused the result. The p-value of 0.54 is consistent with the confidence interval's inclusion of estimates on either side of no difference. It does not establish equivalence or prove the absence of an effect.

The p-value and interval depend on the analysis model and data used. With clustered observations, accounting for within-clinic dependence is important because ignoring it can make standard errors too small or otherwise misstate uncertainty. General: over-dispersion occurs when variability exceeds what a model assumes; a model that fails to accommodate it can give misleading precision. The registry record does not report whether over-dispersion was assessed or how it was handled.

The record also does not report an interim analysis plan, a detailed statistical analysis plan, or a sample-size justification. The separate planning illustration described in the registry is based on the observed effect and specified assumptions; it is not the trial's original design justification and should not be read as observed power. Such illustrations are hypothetical planning aids, not evidence about the probability that the completed trial detected an effect.

10. Analyses Reported by the Sponsor

The reported primary result is the sponsor's mixed models analysis. The registry notes that a simple individual-level re-analysis would be misleading because the trial used a cluster-randomized design. Accordingly, no unadjusted individual-level recalculation is used to replace or supplement the sponsor's estimate.

This distinction matters because a calculation that treats each participant as independent may fail to account for shared clinic-level variation. General: when observations are correlated within clusters, ignoring that dependence can produce an incorrect estimate of uncertainty. A valid analysis must reflect the design and the assumptions needed for the outcome and model. The registry identifies the sponsor's approach as a mixed models analysis, but does not report enough model detail to reproduce it independently.

The sponsor reports a percent difference in median of -0.7, with a 95% confidence interval from -2.9 to 1.5 and p = 0.54. These are the figures to use when describing the primary analysis. The registry record does not provide a separate recalculated estimate for comparison, nor does it report sufficient details to determine whether a different reasonable model would yield the same result. The available account therefore supports interpretation of the sponsor's result, not an independent validation of its computation.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 13 outcome measures and 5 analyses. The primary outcome is spine-related RVUs over 12 months; the listed secondary outcomes include opioid prescriptions, cross-sectional imaging, estimated payer costs, spine surgery, and RVUs over a longer follow-up period. The record does not report a multiplicity adjustment, a hierarchy for testing outcomes, or a prespecified strategy for interpreting multiple comparisons. It is therefore not possible to determine from the registry how the sponsor accounted for the possibility of chance findings across outcomes or analyses.

The registry does not report the number of participants included in the primary endpoint analysis, the analysis population definition, or the handling of missing endpoint data. It is also not reported in the registry record whether the primary analysis followed intention-to-treat principles, how crossovers or departures from assigned reporting conditions were handled, or whether sensitivity analyses were performed. These details affect how the result should be interpreted, especially when outcomes are measured after index imaging and follow-up may be incomplete.

The record does not describe an interim analysis plan, stopping rules, or a detailed statistical analysis plan. It identifies mixed models for the sponsor's primary analysis, but does not state the model specification, adjustment variables, or the assumptions made about missing observations. The primary endpoint population field is blank, and the record does not give a full account of which clusters or participants contributed to the result.

These omissions do not show that the analyses were conducted improperly. They mean that important features of the analysis cannot be independently assessed from the registry record. In particular, the reported confidence interval and p-value should be understood as conditional on an analysis whose full details are not available in the registry description.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: emergency department visit within 90 days of index imaging (11.0%).

The registry's adverse-event figures list a control group with 117455 participants at risk and 12885 affected by serious adverse events. The intervention group is listed with 121431 participants at risk and 13289 affected. Deaths are recorded as 958 in control and 953 in intervention. The record lists zero participants at risk and zero affected for other adverse events in each group.

The most frequent serious adverse event term listed is emergency department visit within 90 days of index imaging, at 11.0%. The registry does not explain the denominator for that percentage in the information, so it should not be interpreted as a rate for a particular arm or as a comparison between arms.

These counts describe the registry's safety entries. They do not establish that the reporting intervention caused or prevented an event. The record does not provide a statistical comparison of the serious-event figures, detail event adjudication, or state whether events were judged related to the intervention. The at-risk counts and affected counts should be read as recorded, without deriving percentages or contrasts from them.

13. What the Result Does, and Does Not, Mean

The primary result describes a comparison of median spine-related RVUs in the 12 months after index imaging. The reported percent difference is -0.7, and the 95% confidence interval ranges from -2.9 to 1.5. The p-value is 0.54. Taken together, these values do not provide clear evidence of a difference in the primary endpoint under the sponsor's mixed models analysis. They do not establish that the two reporting approaches are equivalent, or that their effects are identical.

The confidence interval includes values on both sides of no difference, so the result remains compatible with estimates in either direction. The registry does not report a threshold for a clinically important difference. Consequently, it is not possible to determine from the primary endpoint result alone whether any values within the interval would be important to patients, clinicians, or health systems.

The endpoint measures procedure-related resource use through RVUs. It is not a direct measurement of symptoms, function, or quality of life. A difference in RVUs would not by itself establish whether the care was more appropriate or produced better health outcomes. Conversely, the primary result cannot answer whether every specific service listed among the secondary outcomes changed.

The trial's stated hypothesis concerned subsequent diagnostic and therapeutic interventions, including cross-sectional imaging, opioid prescriptions, spinal injections, and surgery. The primary endpoint is a composite resource measure rather than a direct test of each of those outcomes. The registry lists several of them as secondary outcomes, but their results are not included in the analysis details. Their direction and precision should not be inferred from the primary endpoint.

The result is also specific to the trial's setting and intervention: adding epidemiologic benchmarks to lumbar imaging reports in a pragmatic cluster-randomized crossover study. The registry does not report enough detail about the crossover schedule, analysis population, or model specification to assess all possible influences on the estimate. The clearest conclusion is therefore a statistical one: the sponsor-reported estimate is close to no difference, its confidence interval spans values on both sides of no difference, and the registry does not establish equivalence or resolve the effects on the other outcomes.

14. Why This Trial Matters Statistically

This trial asks a question about how information presented in an imaging report might relate to later care. The intervention is a change in the report itself, not a direct clinical procedure. That makes the design statistically interesting: the intervention is implemented through clinics and can influence practice at a group level, which fits a cluster-randomized approach better than an analysis that assumes all participants were assigned independently.

The crossover designation also makes the interpretation dependent on design details. In general, treatment condition and time can be entangled in crossover studies if periods differ or if effects persist after a clinic changes approach. The registry record does not give the schedule or model details needed to assess those possibilities. Its broad design labels are informative, but they are not a substitute for a full protocol or analysis plan.

The primary outcome combines procedure-related resource use in a single RVU measure. A composite can capture utilization across procedures, but it can also obscure which components drive a result. The listed secondary outcomes may help distinguish specific types of subsequent care, yet the registry entries do not include their estimates. The primary result therefore answers a narrower question than the trial's overall stated goal.

Finally, the estimate and interval illustrate why interpretation should not rest on a p-value alone. The interval includes values on either side of no difference, and the record provides no clinical threshold for judging the importance of those values. That makes precision and endpoint meaning central to the reading: the result does not show a clear difference in the composite measure, but it cannot be treated as proof that the reporting approaches are equivalent.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record leaves several design and analysis details unspecified. It identifies randomized cluster allocation and a crossover model, but does not report the number of clinics, the crossover sequence, the timing of periods, or whether washout was used. These details are relevant to assessing possible period effects, carryover, and how well the statistical model reflects the design.

The record names a mixed models analysis but does not give the model formula, the covariance structure, adjustment variables, or the method used to estimate the percent difference in median. It does not report the analysis population, the number of observations contributing to the primary endpoint, or how missing outcome data were handled. The primary endpoint's population field is blank. These omissions limit independent assessment and reproducibility of the primary result.

Masking is recorded as none. The registry does not explain whether any outcome assessors or analysts were masked, or how the lack of masking was considered in the design. The endpoint is based on recorded procedures, but the record does not provide further information about outcome ascertainment or data validation.

The primary RVU measure captures resource use rather than symptoms or function, and a composite can conceal differences among its component procedures. The registry lists secondary outcomes that could address other dimensions of care, but their results are not available in the reported analysis details. A multiplicity strategy is also not reported in the registry record. These limitations call for a focused interpretation of the primary estimate rather than a broad conclusion about every subsequent test, treatment, or clinical outcome.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Trial of Inserting Prevalence Information Into Lumbar Spine Imaging Reports — NCT02015455.
• Registry record last updated 2022-02-14; status last verified 2022-01.
• Results first posted 2022-02-14.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

The registry identifies NCT02015455 as the Trial of Inserting Prevalence Information Into Lumbar Spine Imaging Reports, with the official title Lumbar Imaging With Reporting of Epidemiology: A Pragmatic Cluster Randomized Trial. It records randomized allocation, no masking, a crossover model, and completed status. The enrollment field is 250401.

The intervention added epidemiologic benchmarks to lumbar imaging reports; usual care used typical reports without those benchmarks. The primary outcome was median spine-related RVUs over 12 months. The sponsor-reported mixed models analysis gave a percent difference in median of -0.7, with a 95% confidence interval from -2.9 to 1.5 and p = 0.54.

The registry also lists secondary outcomes involving opioid prescriptions, cross-sectional imaging, payer costs, spine surgery, and RVUs at a longer follow-up. Their estimates are not included in the primary result. Details of the analysis population, missing-data handling, multiplicity strategy, and full crossover and model specifications are not reported in the registry record.