Validation Study of Physical Measurement of Tophi: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Validation Study of Physical Measurement of Tophi (NCT00175006), a registered phase not stated study. The primary outcome is Average Percent Difference in Area Between Visits.

2. Clinical Question

The study purpose was to assess inter-rater and intra-rater reproducibility. In general, inter-rater reproducibility concerns agreement among raters, while intra-rater reproducibility concerns consistency when a rater repeats a measurement. These are measurement properties, rather than comparisons of the clinical effects of different treatments.

The primary outcome description focuses on the difference in measured tophus area between visits. Measurements were made at Visit 1 (Day 1) and Visit 2 (Days 6-11), with the visits separated by no more than 10 days. The registry states that change in tophus size over 10 days was not expected. This provides the rationale for treating differences between visits as relevant to measurement reproducibility, although the record does not report a numerical result that would show the size of those differences.

The registry record does not describe a distinct comparator group, a random allocation process, or an intervention intended to change the tophi. The central question is therefore whether the measurement procedure gives consistent readings, not whether a treatment improves gout or changes nodule size.

3. Trial Design

This is a completed measurement-validation study listed under the title “Validation Study of Physical Measurement of Tophi.” The official title describes assessing a direct physical measurement method for evaluation of tophus nodules in subjects with gout. The condition listed is gout, and the sponsor is Takeda. The study start is recorded as 2002-11 and primary completion as 2003-01.

The registry reports enrollment of 13. The listed group is “Tophi Participants”; its arm description is blank. The intervention is “Measurement of Tophi to validate procedure,” categorized as OTHER. No randomized treatment allocation, treatment-control comparison, or separate comparator group is described. The registry record does not report the allocation method or a more detailed protocol for assigning raters or measurement tasks.

The primary outcome description says that length and width were measured at two visits. Visit 1 was on Day 1; Visit 2 was on Days 6-11. The visits were separated by no more than 10 days. Measurements of 52 tophi were obtained at those visits from the enrolled subjects. The record says that change in tophus size over 10 days was not expected and that the calculation pooled measurements across raters.

The study's stated purpose refers to both inter-rater and intra-rater reproducibility. However, the registry record does not report separate numerical estimates for these forms of reproducibility, nor does it specify how many raters participated or how raters were allocated to measurements. The primary outcome description gives a visit-based summary rather than separate agreement results by rater.

The registry lists two outcome measures and zero analyses. The primary outcome is described, but the numerical outcome value and its standard deviation are not reported in the registry record. Details of a statistical analysis plan, sample-size justification for the validation study, and interim analyses are not reported in the registry record.

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

Analysis population for the primary outcome, as defined in the registry: Measurements of 52 tophi were obtained at 2 separate visits separated by no more than 10 days from the 13 subjects enrolled. Change in tophus size over 10 days was not expected.

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 Average Percent Difference in Area Between Visits, measured over Visit 1 (Day 1) and Visit 2 (Days 6-11).

The primary endpoint is titled “Average Percent Difference in Area Between Visits.” It is intended to describe how much measured tophus area varies between the two visits. The record says that the rater measured length and width in mm at each visit, and that the area summary used the absolute difference between Visit 1 and Visit 2 divided by their average, calculated for the same tophus and pooled across raters.

In general, an absolute difference focuses on the size of a discrepancy rather than whether the later value is larger or smaller. Relating that discrepancy to the average of the paired measurements expresses it relative to the measurement scale. Such a summary can help describe repeatability when actual biological change is not expected over the measurement interval. It does not, by itself, identify the source of disagreement or show whether agreement differs across raters.

The registry record lists the endpoint unit as mm², while its description calls the measure an average percent difference. Those labels do not appear to describe the same type of unit, and the record does not explain the discrepancy. The specific method used to convert length and width into area is also not reported in the registry record.

The endpoint definition is available, but its observed mean and standard deviation are not reported in the registry record. Consequently, the size and precision of the visit-to-visit differences cannot be assessed from the registered outcome information.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical description centers on a continuous measurement and a paired comparison across visits. The registry says that tophus length and width were measured at Visit 1 and Visit 2, and that the primary summary was an average percent difference in area. It also states that the calculation was made for the same tophus and pooled across raters.

What does a continuous endpoint represent?

In general, a continuous endpoint can take a range of measured values rather than being limited to categories such as present or absent. For this study, the underlying observations were physical dimensions, and the endpoint description refers to area and a relative difference between visits. A mean summarizes the central level of a continuous measure; a standard deviation describes how spread out the observations are around that mean. These statistics answer different questions: the mean describes the average result, while the standard deviation describes variation among the measured results.

The registry identifies the parameter as a mean and dispersion as a standard deviation. However, neither the numerical mean nor the numerical standard deviation is reported in the registry record. The endpoint's listed unit is mm², while the description defines a percent difference. That inconsistency should be kept in view rather than silently resolved. The record does not state whether the unit is a labeling error or how it should be interpreted.

Why compare measurements from the same tophus?

In general, a paired comparison uses two measurements taken on the same unit, so that the comparison concerns within-unit change rather than a contrast between unrelated units. Here, the outcome description explicitly refers to Visit 1 and Visit 2 measurements for the same tophus. The registry says that 52 tophi were measured at the two separate visits from the 13 subjects enrolled. It does not provide further detail about how multiple tophi within a subject were handled statistically or whether clustering by subject was considered.

The visits were separated by no more than 10 days. The record states that change in tophus size over 10 days was not expected. In general, that assumption makes visit-to-visit differences informative about measurement consistency, because an expected biological change would otherwise contribute to the difference. It remains an assumption described by the registry, not a numerical finding about what happened to the tophi during the study.

How is the endpoint described?

The registry defines the calculation as the absolute difference between Visit 1 and Visit 2 divided by the average of those two measurements, for the same tophus, and pooled across raters. In general, taking an absolute difference removes direction: the summary reflects the size of the gap, not whether one visit's measurement was higher or lower. Dividing by the average makes the difference relative to the measurement level. This type of relative summary can help compare discrepancies across observations with different measurement scales.

The description does not provide further operational details about the area calculation, handling of repeated readings, or pooling procedure. It also does not explain how the stated average was formed across tophi or raters. The intended endpoint is therefore identifiable, but some implementation details are not reported in the registry record.

What would an uncertainty interval add?

In general, a confidence interval describes a range of values compatible with the data and an estimation procedure, and communicates uncertainty around an estimate. It is not a guarantee that the true value lies in that particular interval. A standard deviation instead describes dispersion among observations and is not itself an interval for the mean. Both can be useful, but they answer different questions.

No confidence interval or numerical standard deviation is reported for the primary endpoint. The record also reports zero analyses, so it does not identify an inferential model or a formal hypothesis test for the primary result. Without the result and its uncertainty, the precision of the estimated measurement difference cannot be assessed.

What is the status of the planning assumptions?

The registry describes planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two hypothetical arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. These are planning assumptions, not evidence of the study's own design or a report of observed power. The record does not report the actual numerical planning values in the registry record for this account, nor does it report a sample-size justification for the validation study.

Those planning assumptions describe a hypothetical two-arm comparison, whereas the registry lists the Tophi Participants group and no separate comparator. They should not be read as a description of the study's measurement design. In general, a sample-size illustration estimates how many participants per arm might be needed under specified assumptions; it does not show that an estimate is precise merely because a study enrolled participants. Here, the primary numerical result needed to connect planning assumptions with observed performance is not reported in the registry record.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Tophi Participants")
n   <- c(13)
m   <- c(29)
sp  <- c(33)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Tophi Participants  13  29.000  33.000  9.058  48.942

11. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures, but the primary outcome is the only one described in detail in the record used for this account. The other outcome's title, definition, timing, and result are not reported in the registry record. The record reports zero analyses. It does not describe a multiplicity adjustment, a prespecified hierarchy of outcomes, or which endpoint would govern any formal inference.

Multiplicity concerns the interpretation of several statistical tests or outcomes. In general, when many tests are considered, the chance of at least one apparently unusual result can increase; methods such as prespecified outcome hierarchies or adjustments may address that issue. No such strategy is reported in the registry record, so it is not possible to say how multiple outcomes were handled. The absence of a reported strategy does not establish that no strategy was used outside the registry record.

Missing-data handling is not reported in the registry record. There is no description of missing measurements, reasons for missingness, imputation, or a complete-case approach. The outcome population description states that measurements of 52 tophi were obtained at two visits from the 13 subjects enrolled, but does not explain whether any planned measurements were unavailable or how incomplete pairs would have been handled.

The record does not define a separate analysis population or provide participant-level flow information. It does not say whether all enrolled subjects were included in every analysis, whether all measured tophi contributed to the primary summary, or how measurements within subjects were treated. These omissions limit assessment of selection and analysis decisions. The endpoint definition and the described measurement population are useful, but the registry record does not provide enough detail to evaluate missingness, multiplicity, or analysis-population choices.

12. 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.

The registry reports zero serious adverse events among the 13 participants at risk for serious adverse events. It also reports zero other adverse events among the 13 participants at risk for other adverse events. No serious adverse-event terms are listed. Deaths are not reported in the registry record.

In general, an adverse-event count describes events recorded under the study's reporting approach; it does not by itself establish whether an event was caused by an intervention. This study is described as a measurement validation study, and the registry does not identify a treatment-control comparison for safety. The zero counts should therefore be read as the reported event counts for the listed participant group, not as a comparative estimate of safety or a demonstration that no risk exists.

The registry does not provide additional detail on event definitions, event surveillance, severity grading beyond the serious/non-serious distinction, or the duration of safety follow-up. It also does not describe how adverse events were attributed. Those details are not reported in the registry record, so the event counts have limited context for interpretation.

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

This study addresses a measurement question: whether direct physical measurement of tophus nodules gives consistent results across visits and raters. The registry identifies the intended endpoint and explains how visit-to-visit differences were defined. It reports that measurements were taken at Visit 1 (Day 1) and Visit 2 (Days 6-11), with no more than 10 days between visits, and states that change in tophus size over 10 days was not expected.

The registry record does not report the numerical primary outcome result. It therefore does not show how large the average percent difference was, how variable the observations were, or how precisely the study estimated the measurement difference. It also does not report separate numerical results for inter-rater and intra-rater reproducibility. The study's stated aim should not be mistaken for a reported finding that the measurement method was reproducible to any particular degree.

This record also does not establish a treatment effect. It describes a measurement procedure and does not present a treatment-control comparison. The endpoint concerns differences in measurements of tophi across visits, not a clinical change attributed to a therapy. No conclusion about treatment benefit or lack of benefit follows from the registered information.

The enrollment of 13 and measurement of 52 tophi describe the recorded study scope, but those figures do not substitute for an estimate with uncertainty. The registry lists a mean and standard deviation as the summary approach, yet does not report their values. The unit labeling also warrants caution: mm² is listed, while the outcome definition uses the language of percent difference. The record does not resolve that inconsistency.

The most defensible reading is that the study was designed to evaluate a practical physical measurement method in subjects with gout, with repeated visit measurements intended to inform reproducibility. The registry provides the rationale and broad calculation, but the missing numerical results prevent assessment of the observed consistency or its precision.

14. Why This Trial Matters Statistically

Measurement quality matters because clinical research relies on measurements that distinguish actual variation from inconsistency in how observations are collected. For a physical feature such as a tophus nodule, measurement differences can arise from the method, the person measuring, or changes in the feature itself. A validation study can help characterize these sources and inform whether a measurement procedure is sufficiently consistent for its intended research use.

This study's design focuses on repeated measurement of the same tophus across visits, rather than comparing separate treatment groups. The registry's statement that change in tophus size over 10 days was not expected gives the visit comparison its measurement-reproducibility rationale. Its stated interest in both inter-rater and intra-rater reproducibility also highlights that agreement among raters and consistency within a rater are distinct questions.

The statistical reporting is important to that purpose. A definition of the endpoint explains what quantity was intended, but the numerical estimate and its variability are needed to judge the observed level of consistency. The registry record does not report the primary mean or standard deviation, and it provides no separate inter-rater or intra-rater estimates. Thus, the record offers a useful description of the validation question but not enough outcome information to quantify the method's performance.

The record also illustrates why endpoint labels and definitions need to align. The listed unit is mm², while the description refers to a percent difference. Such ambiguity can affect how a result is understood, even when the calculation is otherwise described. Clear reporting of the analysis population, handling of repeated measurements, and uncertainty would further support interpretation. Those details are not reported in the registry record.

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 main limitation for interpreting this study is that the registry record does not report the numerical primary outcome result. The mean average percent difference and standard deviation are not available, so the observed magnitude and variability of visit-to-visit measurement differences cannot be evaluated. No confidence interval or other measure of uncertainty is reported.

The stated aim includes inter-rater and intra-rater reproducibility, but the primary endpoint description gives a pooled summary across raters. Separate estimates for agreement between raters and repeatability within a rater are not reported in the registry record. The number of raters, their roles, and the procedure for assigning or repeating measurements are also not reported.

The endpoint definition and its listed unit are not fully aligned: the title and description refer to an average percent difference, while the unit is mm². The registry does not explain this discrepancy. It also does not specify how measured length and width were combined to define area or provide detail on the pooling method.

The record states that 52 tophi were measured at two visits from the 13 subjects enrolled, but does not report how multiple tophi within a subject were accounted for statistically. It does not describe missing measurements, missing-data handling, or a clearly defined analysis population. These omissions make it difficult to assess whether observations were complete and how dependence among measurements was treated.

Finally, the registry does not report a statistical analysis plan, sample-size justification for the validation study, or interim analyses. The planning assumptions described for sample-size illustrations refer to a hypothetical two-arm design and should not be taken as evidence about the study's own design. These limitations concern the information available in the registry record; they do not establish what analyses or procedures may have been documented elsewhere.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Validation Study of Physical Measurement of Tophi — NCT00175006.
• Registry record last updated 2010-07-27; status last verified 2010-07.
• Results first posted 2009-07-16.
• 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

NCT00175006 is a completed study titled “Validation Study of Physical Measurement of Tophi,” sponsored by Takeda and listed for subjects with gout. Its start is recorded as 2002-11 and primary completion as 2003-01. Enrollment was 13, with the group named “Tophi Participants.” The intervention is described as measurement of tophi to validate the procedure.

The stated purpose was to assess inter-rater and intra-rater reproducibility of direct physical measurement. Length and width were measured at Visit 1 (Day 1) and Visit 2 (Days 6-11), separated by no more than 10 days. The primary outcome was average percent difference in area between visits, described as an absolute difference relative to the average of the paired measurements and pooled across raters. Measurements of 52 tophi were obtained from the enrolled subjects.

The registry lists two outcome measures and zero analyses. It does not report the numerical primary result, its standard deviation, or separate reproducibility estimates. The registry reports zero serious and zero other adverse events in the listed participant group; deaths are not reported in the registry record.