PRESTIGE Observational Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for PRESTIGE Observational Study (NCT00875810), a registered phase not stated study. The primary outcome is EQ-5D.

2. Clinical Question

The study record describes prospective observational collection, with quality of life as its main focus. That design can describe outcomes among participants who underwent the procedure, but without a stated comparator it cannot isolate how much of an observed change is attributable to the surgery rather than other influences. In this registry record, even a descriptive assessment of EQ-5D change is not possible because the endpoint values and analysis are not reported.

3. Trial Design

The PRESTIGE Observational Study is registered as completed and lists enrollment of 194 participants with degenerative cervical disc disease. Its stated purpose was to collect prospective observational data, primarily on quality of life, in connection with cervical disc surgery using the PRESTIGE Cervical Disc System. The registry lists the study start as 2008-04 and primary completion as 2013-11.

This is not described as a randomized trial. Allocation is not stated, and no like-for-like control comparison is identified. The registry group is “Cervical Arthroplasty + Prestige LP.” The study description presents the procedure as an alternative to surgical fusion, but that framing does not mean the registry includes a fusion comparison group. Any results from the observed group would describe participants in that setting rather than establish a treatment contrast.

The primary outcome is EQ-5D, recorded as a continuous measure with the mean and standard deviation specified as the summary statistics and a timeframe of 2 years. The objective describes quality of life before and after surgery and also names the Neck Disability Index. Secondary outcomes listed are duration of pain prior to enrollment and intervertebral disc space. The registry record lists four outcome measures overall, but numerical results are not reported for the primary endpoint in the registry record for this study.

Although enrollment is reported, the number analyzed for EQ-5D is not. The record explains that not all patients completed questionnaires and that the analyzed count differs from the Participant Flow total. The statistical analysis plan, participant-level analysis population, and handling of missing measurements are not reported in the registry record. The completed status and stated study dates do not establish that every participant completed every assessment.

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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: As this is an observational study not all patients completed EQ-5D questionnaires, for this reason the number of participants analyzed is different from the number of patients in the Participant Flow.

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.

6. Primary Endpoint

The registry lists the primary outcome as EQ-5D, measured over 2 years.

EQ-5D is a health-related quality-of-life instrument. The registry description says it covers mobility, self-care, usual activities, pain or discomfort, and anxiety or depression, and includes a Visual Analog Scale that patients can use to rate their health. Each dimension has three response levels: no problems, some problems, and extreme problems. The EQ-5D index has an upper limit of 1 for full health, while 0 represents death; scores below 0 are possible for health states judged worse than death.

Quality of life is relevant to the study’s stated objective because it captures the patient’s assessment of health across several domains, rather than focusing only on a structural or procedural measure. The description proposes documenting quality of life before and after surgery, with EQ-5D identified as the primary outcome at 2 years. The record also names the Neck Disability Index in its objective, but the numerical EQ-5D result and the details needed to interpret any change are not reported in the registry record.

The endpoint is specified as a continuous measure summarized by a mean and standard deviation. These statistics would describe the average score and its variability among the participants included in an analysis. They do not, by themselves, show how many participants improved, whether any change was clinically important, or whether change was caused by surgery. Those interpretations would require reported values, an analysis description, and an appropriate basis for comparison.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry specifies EQ-5D as a continuous outcome summarized using a mean and standard deviation, with assessment at 2 years. These choices describe the intended form of the result, not the analysis actually performed. The numerical summary and analytic details are not reported in the registry record, so the method used to compare assessments or handle the questionnaire data cannot be established.

What a mean describes

In general, a mean is the arithmetic average of the observed measurements in an analysis group. For an EQ-5D result, it would provide a compact description of the average index score among the participants whose measurements were included. It does not show the distribution of individual scores. Participants may have different health profiles even when their average is the same, and a mean alone does not indicate how many people experienced a particular outcome.

The standard deviation describes the spread of measurements around the mean. In general, a larger standard deviation indicates more variation among the included observations, while a smaller one indicates scores are more concentrated around the average. It is not the same as the uncertainty in the estimated mean. A standard deviation and a confidence interval answer different questions: the former describes variability among observed participants, and the latter describes uncertainty about an estimated quantity under a specified statistical model. No confidence interval is reported for the EQ-5D endpoint in the registry record.

What the EQ-5D scale means

The registry description states that the instrument covers mobility, self-care, usual activities, pain or discomfort, and anxiety or depression, as well as a Visual Analog Scale for patient-rated health. The index has an upper limit of 1, with 0 representing death, and scores below 0 are possible. The scale therefore should not be interpreted as an ordinary measure that is necessarily bounded at 0. The score’s meaning depends on the instrument’s scoring and the health states it represents; the registry entry does not provide the participants’ score distribution.

Because the outcome is continuous, a mean-based summary can be useful for describing an overall level. However, bounded or discrete-valued health scores may not have a symmetric distribution. In general, readers may also want to know the distribution, the proportion at particular score levels, or other summaries that are less sensitive to extreme values. None of those additional summaries is reported for the primary endpoint in the registry record.

Change over time and within-person data

The primary objective describes documenting quality of life before and after surgery. For repeated measurements on the same people, the observations are related: a participant’s later score is not statistically independent of that participant’s earlier score. In general, an analysis of change should account for this pairing or otherwise model the repeated measurements appropriately. A comparison of two group means that ignores within-person relationships can answer a different question and may represent uncertainty differently.

The record does not state whether the analysis used paired changes, a repeated-measures model, a comparison of means, or another method. It also does not provide the baseline and follow-up means, a change estimate, or a measure of uncertainty. Accordingly, no particular analysis method can be attributed to this study. The registry’s designation of a mean and standard deviation does not establish how changes between assessments were tested.

Why variation and over-dispersion matter

In general, over-dispersion refers to data varying more than a statistical model expects. It is often discussed for count outcomes, where observed variability exceeds the assumptions of a basic count model. EQ-5D is listed as a continuous outcome, so a count-model explanation should not be mistaken for a method used in this study. More generally, model assumptions should fit the scale and distribution of the outcome. The record does not report model diagnostics or a model for the primary endpoint.

For a mean-based analysis, variation among individuals affects how precisely the average is estimated. The standard deviation would help describe that observed variation, while the number of measured participants would also be needed to assess precision. Neither the primary endpoint’s numerical spread nor its analyzed sample size is reported. No recalculated estimate can be made from the registry information described.

Association is not a treatment contrast

The study is observational, allocation is not stated, and there is no identified like-for-like control group. In general, observing scores before and after an intervention can describe temporal change but cannot on its own separate intervention effects from other changes over time. A randomized comparison is one way to support a causal contrast, but the registry does not describe a randomized allocation or comparator for this study. It would therefore be inappropriate to present a within-group change, even if one were available, as a controlled estimate of the effect of the device.

The registry lists zero analyses. This signals that no analyses are displayed in the registry entry, not that an analysis of any kind was necessarily never performed. The statistical plan, method for estimating uncertainty, and prespecified contrasts are not reported in the registry record. Without those details and the underlying endpoint results, the appropriate statistical reading is limited to the outcome definition and the study design rather than an estimate of effect or precision.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures. It identifies EQ-5D as the primary outcome and lists duration of pain prior to enrollment and intervertebral disc space as secondary outcomes. The objective also names the Neck Disability Index. The registry record does not provide numerical results or analyses for these outcomes in the information available for this study.

In general, multiplicity arises when several outcomes, time points, subgroups, or statistical comparisons are examined. The more questions tested, the greater the chance that at least one result appears notable by chance if each is assessed without accounting for the set of tests. A statistical plan can clarify which analyses are primary and how secondary analyses are interpreted. The plan for controlling or addressing multiplicity is not reported in the registry record. The listed outcome count alone does not reveal how many tests were planned or performed.

Missing endpoint data are a separate concern. The registry states that not all patients completed EQ-5D questionnaires and that the number analyzed differs from the Participant Flow total. The exact number with measurements, the reasons for missing questionnaires, and the method used to handle missing data are not reported in the registry record. In general, an analysis restricted to participants with observed questionnaires can be affected if questionnaire completion is related to health status or other factors. Whether that occurred cannot be determined from the record.

The registry lists enrollment of 194, but this is not an endpoint-specific analysis count. The analysis population and any exclusions are not reported. The registry also lists zero analyses; no displayed analysis should therefore be assumed to have addressed multiplicity, missingness, or the repeated nature of assessments.

11. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: lumbar pain (1.1%), syndroma carpi radialis (0.5%), arm pain (0.5%), quervain syndrome (0.5%), thoracic spine discopathy (0.5%).

The registry lists one group, “Cervical Arthroplasty + Prestige LP.” For serious adverse events, 190 participants were at risk and 7 were affected. For other adverse events, 190 were at risk and 40 were affected. These are separate categories of registry counts and should not be combined or treated as comparative estimates. No percentages need to be inferred from these counts to describe what the record reports.

The listed serious-event terms include lumbar pain (1.1%), syndroma carpi radialis (0.5%), arm pain (0.5%), Quervain syndrome (0.5%), thoracic spine discopathy (0.5%), and wound hematoma (0.5%). The registry record does not explain whether these terms are mutually exclusive, how repeated events were handled, or whether the listed terms exhaust the serious events. Deaths are not reported in the registry record.

These figures describe events recorded in the listed group; they do not establish a comparative safety difference. The study is observational, allocation is not stated, and no like-for-like control group is identified. The event counts should therefore be interpreted as descriptive registry information, not as evidence for a causal comparison.

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

The registry record establishes that the PRESTIGE Observational Study focused on prospective collection of quality-of-life information around cervical disc surgery. It names EQ-5D as the primary endpoint, specifies a 2 years timeframe, and describes mean and standard deviation as the intended summaries. It also explains the EQ-5D domains and scale. These details clarify what the study set out to document.

The record does not report the numerical EQ-5D results, the number analyzed for that outcome, or an estimate of change. It therefore cannot establish the average quality-of-life score among analyzed participants, the variation in those scores, the precision of an estimate, or the pattern between assessments. Nor does it allow assessment of how missing questionnaires may have affected any result. The registry lists zero analyses, so no statistical test or confidence interval can be interpreted from the entry.

Even if a within-person change estimate were available, the observational design would matter. Allocation is not stated, and no like-for-like control group is identified. A change over time in a treated group would not by itself show what would have happened without the procedure, or separate the procedure from other influences. The record therefore does not support a causal treatment comparison.

The adverse-event counts provide descriptive information for the single listed group. They do not provide a comparative estimate, and deaths are not reported in the registry record. The study status is completed, but that status does not fill the gaps in endpoint results or analysis details.

In general, a registry entry can define the question and outcome even when it does not contain enough information to evaluate the result. In this case, the outcome’s intended interpretation is understandable, but the posted record does not provide the values needed to characterize the observed quality-of-life findings. The appropriate conclusion is limited to the study’s design, stated objectives, and recorded event counts—not a claim that the intervention did or did not improve health.

13. Why This Trial Matters Statistically

This study is statistically notable for the distinction between a clearly described outcome and an outcome result that is not reported in the registry record. EQ-5D is identified as the primary measure, its domains and scale are described, and the summary form and timeframe are specified. Yet without the mean, standard deviation, analyzed count, or an estimate of change, readers cannot quantify the observed quality-of-life pattern.

The registry also makes an important analysis-population issue explicit: not all patients completed EQ-5D questionnaires, and the number analyzed differs from the Participant Flow total. This signals why enrollment and endpoint sample size are not interchangeable. For a continuous outcome, the number with usable measurements and the variability of those measurements both inform precision. The endpoint-specific count and variability are not reported.

The observational design is another central statistical feature. It can describe collected outcomes in the study group, but no comparator is identified and allocation is not stated. This matters because temporal change and treatment effect are not the same estimand. Without a comparison that addresses what might have occurred otherwise, the record cannot support a causal contrast.

Finally, the registry lists four outcome measures and zero analyses. That combination makes the boundary of interpretation especially clear: readers can identify the intended measurement framework, but cannot review displayed statistical results or determine how multiple outcomes, missing questionnaires, or repeated measurements were handled. These limitations are useful to recognize when interpreting clinical registry records more broadly.

14. 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 main limitation is the absence of numerical primary endpoint results in the registry record. EQ-5D is designated as the primary outcome at 2 years, but no mean, standard deviation, change estimate, confidence interval, or test result is reported. The number of participants analyzed for EQ-5D is also not reported, despite the record’s note that not all patients completed questionnaires.

The record does not describe the statistical analysis plan, the handling of missing data, or the analysis population. It does not establish whether the before-and-after measurements were analyzed as paired observations or by another approach. It also does not report whether additional outcome analyses were adjusted for multiplicity. These details cannot be inferred from the fact that mean and standard deviation are named as summaries.

Because this is an observational study with allocation not stated, and no like-for-like control group identified, the design does not provide a stated randomized treatment comparison. The study description mentions surgery before and after assessments, but the record does not give enough information to separate temporal change from a causal effect of the procedure.

Enrollment of 194 does not supply the missing endpoint-specific denominator. The adverse-event counts use 190 participants at risk for each listed category, but the record does not explain the relationship between those counts and the analyzed EQ-5D population. The registry lists four outcome measures and zero analyses; the record does not establish whether analyses were conducted elsewhere. Deaths are not reported in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: PRESTIGE Observational Study — NCT00875810.
• Registry record last updated 2016-01-28; status last verified 2016-01.
• Results first posted 2015-03-17.
• 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.

18. Record Summary

The PRESTIGE Observational Study is listed as completed, with enrollment of 194 participants and a study start of 2008-04. Primary completion is listed as 2013-11. The study concerns degenerative cervical disc disease and prospectively collected observational data focused primarily on quality of life after cervical disc surgery using the PRESTIGE Cervical Disc System.

EQ-5D is the primary outcome, specified as a continuous measure summarized by mean and standard deviation at 2 years. The objective also names the Neck Disability Index. The registry notes incomplete EQ-5D questionnaire completion, but the analyzed count and numerical endpoint results are not reported in the registry record. The record lists four outcome measures and zero analyses.

For the listed group, 7 of 190 participants at risk were affected by serious adverse events and 40 of 190 by other adverse events. The study is observational; allocation is not stated, and no like-for-like control comparison is identified.