The Long-term Value of Preoperative Duplex Before Surgery for Varicose Veins: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Long-term Value of Preoperative Duplex Before Surgery for Varicose Veins (NCT01195623), a randomized na study. The primary outcome is Rate of Re-do Surgery.

2. Clinical Question

The clinical question is whether adding preoperative duplex imaging to clinical assessment is associated with different long-term reoperation counts after varicose vein surgery. The registry brief summary describes earlier assessments at 2 months and 2 years and says the investigation aimed to study results after 8 years, including mechanisms of recurrence. The primary outcome record, however, lists a timeframe of 7 years mean. These descriptions give context for the follow-up question but do not supply a time-to-event analysis or explain the difference in stated follow-up timing.

The registry also lists recurrence rate as a secondary outcome. No secondary result is included in the posted outcome figures, so the primary reoperation count should not be treated as a complete account of recurrence or of all long-term surgical outcomes.

3. Trial Design

This was a randomized, parallel-group trial of preoperative duplex imaging before surgery for primary varicose veins. The registry lists 293 patients and 343 limbs. Participants were assigned to surgery planned with preoperative duplex imaging or surgery planned from clinical examination alone. The trial is marked completed, and Uppsala University Hospital is listed as the sponsor.

The registry records no masking. That means the study is not listed as blinded; it does not establish whether any particular outcome assessment was independently or consistently adjudicated. Further details about allocation concealment, implementation of randomization, or assessor masking are not reported in the registry record.

The primary outcome description says the analysis was conducted on legs and identifies 166 randomized legs in the duplex group and 177 in the no-duplex group. The posted arm results list 124 and 134 alongside the reoperation counts. The record does not explain how those arm counts relate to the randomized leg totals, such as whether they reflect follow-up availability or an analysis population. They should not be treated as interchangeable denominators.

The brief summary describes comparisons of reoperation rates, clinical findings, and duplex findings at 2 months and 2 years, then states that the long-term phase aimed to examine results after 8 years. The primary outcome timeframe is listed as 7 years mean. The registry does not provide a detailed follow-up schedule, reasons for loss to follow-up, or an account of which participants or legs contributed to each time point.

The trial record lists two outcome measures, with one secondary outcome named as recurrence rate. It does not report a statistical analysis plan, a sample-size justification, or analysis results such as an estimated treatment contrast and confidence interval. The observed reoperation counts can therefore be described, but the randomized design alone does not supply the missing statistical details.

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: The number of legs has been analyzed, randomized 166 legs in the duplex group and 177 in the no-duplex group

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 Rate of Re-do Surgery, measured over 7 years mean.

The primary outcome is titled “Rate of Re-do Surgery,” but its measurement is specified as the number of reoperations in legs. The listed timeframe is 7 years mean. The posted values are counts: 15 for surgery with preoperative duplex and 38 for surgery without preoperative duplex. These are event counts, not themselves rates or risks.

Reoperation is a clinically interpretable outcome for a long-term surgical comparison: it records whether another operation was performed on a leg after the initial procedure. Such an endpoint can capture a consequential consequence of the original treatment pathway. It does not, by itself, describe all recurrence, symptoms, clinical findings, or reasons for further surgery. The registry names recurrence rate as a secondary outcome, but does not post a result for it in the record.

To interpret a count as a rate or risk, a reader would need a clearly specified denominator and, for a rate over time, information about follow-up time. The registry gives randomized leg totals in the outcome description and separate arm counts alongside the posted results, but does not explain how these relate. It also does not report a confidence interval or statistical test for the group contrast. Consequently, the counts can be stated as posted, while the precision and inferential meaning of a difference in underlying reoperation experience remain uncertain.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes random allocation to two parallel groups. In a randomized trial, assignment is determined by a chance process rather than by a participant’s or clinician’s choice. General statistical explanation: this design can reduce systematic baseline differences between groups on average, but its strength in practice also depends on how randomization was implemented and maintained. Allocation concealment and implementation details are not reported in the registry record.

The trial is listed as unmasked. General statistical explanation: when treatment assignment is known, expectations can influence some aspects of care, outcome assessment, or reporting, depending on the outcome and the procedures used. Reoperation is a recorded event, but the registry does not state how decisions to reoperate were made, whether they were independently reviewed, or whether outcome assessors were masked. No stronger conclusion about these processes is warranted.

What does a count outcome represent?

The primary endpoint is specified as a number of reoperations in legs. A count records how many events occurred in a defined group. Counts are not automatically comparable as rates if the groups differ in the number of legs observed or in their duration of observation. General statistical explanation: a rate model may account for differing exposure time, while a risk comparison uses events relative to a defined population at risk. The registry does not identify a model for this endpoint or explain the relationship between the randomized leg totals and the arm counts listed with the results.

For count data, a statistical analysis might use a count regression model or a method suited to the study’s design and data structure. Repeated observations, clustering of multiple legs within a patient, and unequal observation periods can affect which analysis is appropriate. General statistical explanation: over-dispersion occurs when observed count variability exceeds what a simple count model expects; ignoring it can make uncertainty estimates too narrow. The registry does not report whether these features were assessed or how they were handled. These are general methodological considerations, not claims about the analysis used in this trial.

What would an effect estimate add?

A treatment-effect estimate would describe the contrast between groups on a stated scale, such as a difference in risks or a ratio of rates, if the necessary data and analysis supported that scale. A confidence interval would communicate uncertainty around that estimate. General statistical explanation: the interval’s width reflects precision under the model and assumptions used; it is not a guarantee that the true effect lies within its endpoints. The registry provides no effect estimate or confidence interval for the primary result, so neither magnitude on a comparative scale nor precision can be assessed.

A p-value, when reported, addresses compatibility between data and a specified null model under the assumptions of the test. It does not quantify the size or clinical importance of an effect. No p-value or test is reported for this primary outcome. It would be inappropriate to reconstruct one from counts when the analysis denominator, data structure, and intended method are unclear.

Why does follow-up matter?

The primary outcome timeframe is listed as 7 years mean, while the brief summary describes an aim to study results after 8 years and refers to earlier assessments at 2 months and 2 years. General statistical explanation: long-term comparisons can be affected by differing follow-up durations, loss to follow-up, and the timing of events. Time-to-event methods can use event timing and account for censoring when their assumptions and data are available. The registry does not provide event times, censoring information, or a time-to-event analysis, so the posted count should not be read as a survival estimate.

The registry identifies 293 patients and 343 limbs, and the primary description gives randomized leg totals of 166 and 177. These data raise a structural issue for interpretation because a patient can contribute more than one limb. General statistical explanation: observations from the same person may be correlated, so an analysis of limbs may need to account for within-person clustering. The record does not state whether such a method was used. This is a consideration raised by the described study structure, not an assertion that any particular analysis was incorrect.

Sample-size planning is distinct from analysis of observed results. General statistical explanation: a planning calculation depends on an assumed effect, variability, significance threshold, power target, allocation, and analysis method. The registry does not report the trial’s own sample-size justification. Any planning illustration based on an observed effect is not observed power and cannot establish that the trial had a particular probability of detecting an effect. No sample-size calculation values for this trial are reported in the registry record.

Overall, the available outcome entry supports descriptive reporting of the two counts. The information needed to evaluate the statistical method—analysis population, denominator, handling of clustering and missingness, model, and uncertainty—is not reported in the registry record. General methods explain what such information would clarify, but they cannot fill in the trial’s unreported analysis.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and names recurrence rate as a secondary outcome. It does not report a multiplicity plan, such as how the interpretation of multiple outcomes or comparisons was controlled. The primary outcome is the number of reoperations in legs; a secondary outcome is named, but no corresponding result is included in the record. The number of analyses is listed as 0, and no analysis details or inferential results are posted.

General statistical explanation: when a study tests multiple outcomes or performs multiple comparisons, the chance of at least one apparently notable result can increase. A prespecified analysis plan can clarify which outcomes are primary and how secondary or exploratory findings will be interpreted. The registry record does not provide that plan, so it is not possible to determine whether the endpoint hierarchy, multiplicity handling, or any subgroup analyses were prespecified.

Missing-data methods and follow-up completeness are not reported in the registry record. The primary outcome description gives randomized leg totals of 166 and 177, while the arm results list 124 and 134. The relationship between these counts is not explained, and the reasons for any difference are not stated. The record does not report whether missing outcomes were imputed, whether analyses included all randomized legs, or whether sensitivity analyses were conducted.

The analysis population is also not described in enough detail to determine whether the posted result follows intention-to-treat principles or another approach. General statistical explanation: the analysis population matters because excluding participants or observations after randomization can affect comparability, particularly when exclusions relate to prognosis or outcomes. Without participant flow and analysis-population definitions, the endpoint counts cannot be assumed to represent all randomized legs.

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.

The registry lists 0 serious adverse events among 148 participants at risk in the duplex group and 0 among 145 participants at risk in the no-duplex group. It also lists 0 other adverse events among 148 and 0 among 145, respectively. These are the figures recorded for the listed safety categories.

These safety counts should be read as reported event counts for the stated groups, not as proof that no adverse events occurred outside the registry’s definitions or observation process. The record does not specify the safety observation period, the criteria used to classify events, or how these safety populations relate to the randomized groups and primary-outcome populations. The number of deaths is not reported in the registry record; a blank death value should not be interpreted as zero.

General statistical explanation: a zero event count does not establish that the underlying event risk is zero. Interpretation depends on the size and definition of the population observed, completeness of follow-up, and how events were collected. The registry gives no confidence interval or comparative safety analysis. The listed figures therefore describe what is recorded, without quantifying the precision of a group comparison or supporting a broader claim about safety.

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

The posted long-term primary outcome counts are 15 reoperations in legs in the group assigned to surgery with preoperative duplex and 38 in the group assigned to surgery without preoperative duplex. The registry’s brief summary characterizes routine preoperative duplex as having led to improvement in earlier results. For the long-term primary outcome, however, the record supplies counts without an inferential comparison, confidence interval, or clarified denominator. Those limits matter when deciding what the figures can establish.

The counts do not establish a reoperation risk or rate because the registry does not explain the analysis denominators or provide exposure-time information. The arm counts listed alongside the results differ from the randomized leg totals in the outcome description, and the record does not explain that relationship. Nor does it report whether observations from two legs belonging to one patient were handled together statistically.

The listed outcome is reoperation, not every form of recurrence or all clinical outcomes. The registry names recurrence rate as secondary, but does not post its result in the record. The counts also do not identify the reasons for reoperation or the recurrence mechanisms that the brief summary says the long-term investigation sought to examine.

General statistical explanation: a randomized design supports a comparative interpretation when follow-up and analysis are appropriately reported, but randomization alone does not supply missing outcome data or uncertainty estimates. A count difference can be a useful descriptive finding while remaining insufficient to establish the precision of an effect or the statistical evidence for a group difference. No p-value or adjusted estimate is reported.

The result therefore communicates the recorded number of reoperations in each group, not a complete estimate of how much preoperative duplex changes long-term outcomes. It does not demonstrate that one strategy works or fails, and it does not resolve the long-term clinical question on its own. The registry’s narrative and its posted numerical outcome should be understood as distinct kinds of evidence.

13. Why This Trial Matters Statistically

This trial raises a useful statistical distinction between a randomized comparison and a fully interpretable comparative result. Randomization determines how groups are assigned; estimating the outcome contrast still requires clear outcome definitions, denominators, follow-up information, and an analysis method. The registry reports the assignment structure and outcome counts, but does not report the details needed to quantify uncertainty around the long-term comparison.

The study also describes both patients and limbs. The brief summary reports 293 patients and 343 limbs, while the primary outcome description gives randomized leg totals. When more than one limb can belong to a participant, the analysis unit and dependence between observations are important. General statistical explanation: treating correlated observations as independent can misstate the precision of an estimate. The registry does not say how this issue was addressed.

Long-term surgical outcomes require attention to follow-up duration and event timing. The listed primary timeframe is 7 years mean, while the brief summary describes an aim to assess results after 8 years. Without follow-up completeness, censoring information, or event-time analysis, a count cannot explain when reoperations occurred or how observation time differed across groups.

Finally, the outcome title says “Rate,” but the result is specified as a count. This illustrates why the measurement scale and denominator should be explicit: counts can be clinically meaningful, but they are not automatically rates or risks. The registry’s limitations do not erase the observed data; they define the boundary between a descriptive finding and a statistically quantified treatment comparison.

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 registry record leaves important details of the long-term outcome analysis unspecified. The primary result is a number of reoperations in legs, while the outcome title calls it a rate. The record does not provide a rate denominator or person-time, and it does not explain how the arm counts of 124 and 134 relate to the randomized leg totals of 166 and 177. This prevents a clear reconstruction of the analyzed populations.

The record also gives differing descriptions of long-term timing: the primary outcome timeframe is 7 years mean, while the brief summary says the long-term phase aimed to study results after 8 years. The record does not explain this distinction or provide the distribution of follow-up. It supplies no event times, loss-to-follow-up information, censoring details, or reasons for missing outcome data.

Although the study randomized patients and limbs, the record does not describe how multiple legs from one patient were handled statistically. It does not report the analysis model, adjustment factors, effect estimate, confidence interval, p-value, or analysis population. Allocation concealment and outcome assessment procedures are also not reported in the registry record.

The registry names a secondary recurrence outcome but does not include its result in the posted outcome entry. It does not report a multiplicity plan, sample-size justification, or detailed protocol for analysis. These omissions limit assessment of endpoint prioritization and the robustness of the reported long-term comparison. The available counts remain descriptive, but the record does not support a precise estimate of comparative long-term reoperation outcomes.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: The Long-term Value of Preoperative Duplex Before Surgery for Varicose Veins — NCT01195623.
• Registry record last updated 2013-02-15; status last verified 2013-02.
• Results first posted 2013-02-15.
• 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 registry record describes a completed randomized, parallel-group trial of preoperative duplex imaging before varicose vein surgery. It lists 293 patients and 343 limbs with primary varicose veins, assigned to surgery planned with duplex imaging or clinical examination alone. The trial is listed as unmasked and sponsored by Uppsala University Hospital.

The primary outcome is the number of reoperations in legs, with a listed timeframe of 7 years mean. The posted counts are 15 for surgery with preoperative duplex and 38 for surgery without preoperative duplex. The outcome description gives randomized leg totals of 166 and 177; the arm results list 124 and 134, and their relationship is not explained. No inferential comparison or uncertainty estimate is reported.

The registry names recurrence rate as a secondary outcome and lists zero serious and other adverse events in the stated safety populations. Details of missing data, analysis populations, statistical methods, multiplicity, and sample-size justification are not reported in the registry record.