This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Diagnosis of Acute Appendicitis: Low-dose Computed Tomography (CT) Versus Standard-dose CT (NCT00913380), a randomized phase 3 study. The primary outcome is Negative Appendectomy.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00913380 |
| Phase | Phase 3 |
| Condition | Appendicitis |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Single |
| Enrollment | 891 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Seoul National University Bundang Hospital |
| Results posted | Yes |
2. Clinical Question
Population
Participants with appendicitis were the condition of interest. The primary outcome population is described more narrowly as participants who underwent non-incidental appendectomy. The registry record does not provide further eligibility details in the information available for this analysis.
Intervention
Low-dose diagnostic CT. The stated purpose was to assess whether this approach was not inferior to standard-dose CT for the rate of unnecessary appendectomy.
Comparator
Standard-dose diagnostic CT. The two groups are described as receiving diagnostic CT; additional details about imaging procedures are not reported in the registry record.
Primary question
Among participants who underwent non-incidental appendectomy, how many had an unnecessary operation, defined as removal of an un-inflamed appendix? The outcome timeframe is 1 week after surgery. The registry record does not report the group-specific primary-outcome counts or an estimate comparing the groups.
The clinical question is framed as a non-inferiority question, not simply as whether the groups differ. To interpret a non-inferiority analysis, readers need the prespecified margin that defines how much worse the intervention could be while still meeting the study’s criterion, together with the estimated group contrast and its uncertainty. The margin and an analysis of the primary outcome are not reported in the registry record, so the stated purpose cannot be evaluated from the posted primary-outcome information.
3. Trial Design
The study is titled “Diagnosis of Acute Appendicitis: Low-dose Computed Tomography (CT) Versus Standard-dose CT,” with an official title focused on the negative appendectomy rate. It is listed as phase 3, randomized, single-masked, and parallel-group. The sponsor is Seoul National University Bundang Hospital. Enrollment is 891, and the status is completed.
The listed interventions are diagnostic CT in both groups, identified as low-dose CT and standard-dose CT. The record does not give further arm descriptions. It also does not state who was masked, how the random sequence was generated, or whether allocation was concealed before assignment. Those details are not reported in the registry record.
The study started in 2009-09, and primary completion was recorded in 2011-04. The primary outcome is the number of participants with unnecessary appendectomies, defined as removal of an un-inflamed appendix. Its timeframe is 1 week after surgery. The stated analysis population comprises participants who underwent non-incidental appendectomy, with the analysis described as intention to treat and complete case.
The registry lists 12 outcome measures, including the primary outcome and secondary outcomes such as additional imaging tests, appendiceal perforation, intervals between clinical events, and CT-report likelihood assessments. The registry record does not provide results for these secondary outcomes in the information. It also does not report a sample-size justification, non-inferiority margin, detailed statistical analysis plan, or interim-analysis plan. These omissions limit what can be inferred about the design rationale and how the trial intended to answer its primary question.
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: None of the enrolled participants were excluded from the trial before assignment to group.
CT Examination
| Stage | Low-dose CT | Standard-dose CT |
|---|---|---|
| STARTED | 444 | 447 |
| COMPLETED | 444 | 447 |
| NOT COMPLETED | 0 | 0 |
Clinical Outcomes
| Stage | Low-dose CT | Standard-dose CT |
|---|---|---|
| STARTED | 444 | 447 |
| COMPLETED | 438 | 441 |
| NOT COMPLETED | 6 | 6 |
Reasons for not completing this period:
| Reason | Low-dose CT | Standard-dose CT |
|---|---|---|
| Lost to Follow-up | 6 | 6 |
Analysis population for the primary outcome, as defined in the registry: Participants who underwent non-incidental appendectomy. Intention to treat. Complete case analysis.
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.
| Characteristic | Unit | Low-dose CT | Standard-dose CT | Total |
|---|---|---|---|---|
| Participants analysed | 444 | 447 | 891 | |
| Age Continuous: Age (year) | year | 29 (21.5 to 36) | 30 (22 to 37) | 30 (22 to 37) |
| Sex: Female, Male: Female | Participants | 276 | 263 | 539 |
| Sex: Female, Male: Male | Participants | 168 | 184 | 352 |
| Race/Ethnicity, Customized: Korean | participants | 441 | 445 | 886 |
| Race/Ethnicity, Customized: Non-Korean | participants | 3 | 2 | 5 |
| Body mass index: < 18.5 (underweight) | kg/m^2 | 62 | 60 | 122 |
| Body mass index: 18.5-24.9 (normal) | kg/m^2 | 312 | 301 | 613 |
| Body mass index: ≥ 25.0 (overweight to extremely obese) | kg/m^2 | 70 | 86 | 156 |
| White blood cell | x10^3/mm^3 | 10.7 (7.8 to 14.1) | 10.8 (8.0 to 14.3) | 10.8 (7.9 to 14.2) |
| Segmented neutrophil | Percentage of peripheral Leukocytes | 77.0 (65.8 to 85.2) | 77.3 (65.5 to 83.9) | 77.3 (65.7 to 84.6) |
| C-reactive protein | mg/dL | 0.5 (0.3 to 2.5) | 0.7 (0.3 to 3.3) | 0.6 (0.3 to 3.1) |
| CT scanner: 16-detector CT | participants | 177 | 191 | 368 |
| CT scanner: 64-detector CT | participants | 154 | 144 | 298 |
| CT scanner: 256-detector CT | participants | 113 | 112 | 225 |
| Radiologist: Abdominal radiologist | participants | 217 | 225 | 442 |
| Radiologist: Non-abdominal radiologist | participants | 227 | 222 | 449 |
6. Primary Endpoint
The registry lists the primary outcome as Negative Appendectomy, measured over 1 week after surgery.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of participants with a negative appendectomy: an operation in which an un-inflamed appendix was removed. The outcome timeframe is 1 week after surgery. This is a binary participant-level outcome when each participant is classified according to whether an unnecessary appendectomy occurred.
This endpoint is used to assess a consequence of the diagnostic pathway. In general, a diagnostic strategy can be evaluated by whether it helps distinguish cases requiring surgery from cases in which surgery would be unnecessary. Comparing the frequency of negative appendectomy between imaging groups can therefore address a clinically relevant aspect of diagnostic performance. That general rationale does not establish how the trial’s actual groups compared.
The registry defines the primary outcome population as participants who underwent non-incidental appendectomy and describes the analysis as intention to treat and complete case. The combination of these descriptions leaves an important interpretive detail: the outcome is defined among a restricted group, but the registry does not explain how the stated analysis population was operationalized. The number of participants included in the primary analysis is not reported in the registry record.
No group-specific negative appendectomy counts, comparison estimate, confidence interval, or test result are reported in the registry record. Consequently, the endpoint definition is available, but the primary outcome findings and their precision cannot be assessed from the posted primary-outcome information.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record establishes that the trial was designed to compare low-dose CT with standard-dose CT and that its stated purpose was to determine whether low-dose CT was not inferior for the rate of unnecessary appendectomy. It does not report the primary-outcome results needed to assess that question. There are no posted group-specific negative appendectomy counts or comparative estimates in the registry record, and no confidence interval or p-value is reported for this endpoint.
This absence matters especially for a non-inferiority question. In general, a non-inferiority conclusion depends on a prespecified margin and on whether the uncertainty around the estimated group difference excludes values that would be considered unacceptably worse. Neither the margin nor a primary-outcome estimate is reported in the registry record. The stated non-inferiority objective therefore cannot be confirmed or rejected from the posted primary-outcome information. Missing results are not evidence that the groups were equivalent, and they do not establish that either approach was better.
The registry does report adverse-event counts. For low-dose CT, 13 participants were recorded as having a serious adverse event, with 444 at risk. For standard-dose CT, 11 participants were recorded as having a serious adverse event, with 447 at risk. Other adverse events were recorded for 1 participant in each group, with the same group-specific numbers at risk. These counts are descriptive. The registry record does not provide a comparative analysis, uncertainty estimates, or additional detail that would support a causal interpretation of the difference in serious-event counts.
The listed serious adverse-event terms include abdominal pain, ileus, wound complication, and fever, with percentages reported in the safety data. The record does not assign those term percentages to particular groups in the information. Death counts are not reported in the registry record.
Overall, the posted information permits a description of the design, endpoint definition, and some safety counts, but not an evaluation of the central primary-outcome comparison. Readers should distinguish the trial’s stated aim from evidence about whether that aim was met. A completed trial status does not substitute for a reported result, and the absence of a primary comparison means that its magnitude and precision remain unknown from the registry record.
9. Statistical Methods Explained
The trial is listed as randomized, single-masked, and parallel-group. In general, randomization is intended to make treatment groups comparable on average with respect to both measured and unmeasured baseline factors. A parallel design assigns participants to one group for the comparison rather than comparing each participant under both approaches. The registry confirms these broad design features, but sequence generation, allocation concealment, and the identity of the masked parties are not reported in the registry record.
What does the primary outcome count?
The primary outcome is a count of participants with an event, not a continuous measurement. The event is an unnecessary appendectomy, defined as removal of an un-inflamed appendix. In general, a binary outcome records whether each participant did or did not experience the defined event during the specified timeframe. For a comparison between groups, analysts may report event counts and proportions, a measure of the difference or relative association, and an interval expressing uncertainty. The registry record does not report those comparative primary-outcome results.
What is required to assess non-inferiority?
Non-inferiority analysis asks whether the intervention is not unacceptably worse than the comparator according to a prespecified tolerance. In general, the tolerance is expressed as a non-inferiority margin on a chosen effect scale. The margin must be interpreted alongside the estimated contrast and its confidence interval; a point estimate alone does not convey whether plausible values cross the margin. The registry record states a non-inferiority objective but does not report the margin, the effect scale, the primary comparison, or its confidence interval. It is therefore not possible to reproduce or assess a non-inferiority conclusion from the posted primary-outcome information.
How should uncertainty be read?
In general, a confidence interval describes a range of values compatible with the data and the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval, while an interval spanning important values may leave the practical interpretation uncertain. A p-value addresses compatibility with a specified null hypothesis under an analysis model; it does not measure the probability that a treatment works or that a conclusion is true. Neither a confidence interval nor a p-value for the primary outcome is reported in the registry record.
The registry states that the primary-outcome population consists of participants who underwent non-incidental appendectomy and describes the analysis as intention to treat and complete case. In general, intention-to-treat analyses retain participants in their randomized groups, while complete-case approaches use participants with observed outcome information. These descriptions can raise questions about how the population restriction and missing outcomes were handled together. The registry record does not explain the implementation, report the number analyzed, or describe missing primary-outcome data.
There are 12 registered outcome measures and 0 analyses listed. In general, when several outcomes or analyses are considered, multiplicity can increase the chance of at least one apparently notable result if no adjustment or prespecified hierarchy is used. The registry record does not report a multiplicity strategy, a hierarchy among outcomes, or an analysis plan that would clarify how multiple comparisons were to be handled. It is therefore not possible to determine how multiplicity was addressed.
The record gives an illustration framework for sample-size calculations based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such calculations, in general, are planning illustrations and not observed power. The registry record does not report the trial’s own sample-size justification or the assumptions used in its design. No inference about the original design rationale should be drawn from an illustrative calculation.
Finally, the record lists adverse-event counts by group, but does not provide a statistical comparison of those counts. In general, event counts should be interpreted in light of the population at risk, outcome definitions, follow-up, and uncertainty. The listed figures alone do not show whether any apparent group difference is statistically distinguishable from chance, nor do they establish that the CT strategy caused an event.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 12 outcome measures, including negative appendectomy and several secondary outcomes. It lists 0 analyses. A list of outcomes does not establish which analyses were planned, which were primary in the analysis plan, or whether any adjustment for multiple comparisons was intended. A prespecified hierarchy or multiplicity procedure is not reported in the registry record.
The primary outcome population is described as participants who underwent non-incidental appendectomy, with an intention-to-treat, complete-case analysis. The record does not state how participants who did not undergo appendectomy were handled, how the analysis population was defined in practice, or how the intention-to-treat description was reconciled with the population restriction. The number included in the primary analysis and the amount or pattern of missing outcome data are not reported in the registry record.
In general, missing outcome data can affect both the precision and the validity of an estimate, particularly if the probability of missingness differs between groups or is related to the outcome. Complete-case analysis uses cases with observed information, but its interpretation depends on assumptions about why data are missing. The registry record does not report missing-data assumptions, sensitivity analyses, or imputation methods.
The protocol’s non-inferiority margin, sample-size justification, analysis model, and interim-analysis plan are also not reported in the registry record. These omissions prevent a full assessment of the intended statistical safeguards and the robustness of the primary analysis. Because primary-outcome estimates are not reported, no sensitivity or multiplicity assessment can be made from the posted results.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Low-dose CT | 13 | 444 | 2.9% |
| Standard-dose CT | 11 | 447 | 2.5% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Low-dose CT | 1 of 444 |
| Standard-dose CT | 1 of 447 |
Most frequent serious adverse event terms
| Event term | Organ system | Low-dose CT | Standard-dose CT |
|---|---|---|---|
| Abdominal pain | Gastrointestinal disorders | 6 of 444 | 6 of 447 |
| Ileus | Gastrointestinal disorders | 4 of 444 | 4 of 447 |
| Wound complication | Injury, poisoning and procedural complications | 3 of 444 | 0 of 447 |
| Fever | General disorders | 0 of 444 | 1 of 447 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Low-dose CT | Standard-dose CT |
|---|---|---|---|
| Abdominal pain | Gastrointestinal disorders | 1 of 444 | 1 of 447 |
Serious events with the highest arm-level rate: abdominal pain (1.4%), ileus (0.9%), wound complication (0.7%), fever (0.2%).
The registry reports serious adverse events separately for the two CT groups. In the low-dose CT group, 13 participants were recorded with serious adverse events among 444 at risk. In the standard-dose CT group, 11 participants were recorded with serious adverse events among 447 at risk. The record also lists 1 participant with other adverse events in each group, with 444 and 447 at risk, respectively.
These are counts of participants, not a statistical comparison. The registry record does not report confidence intervals, p-values, adjusted estimates, or a causal analysis for these safety figures. The counts alone cannot establish whether the groups differ in safety or explain why an event occurred. The definition and ascertainment details for these categories are not reported in the registry record.
The listed serious adverse-event terms are abdominal pain (1.4%), ileus (0.9%), wound complication (0.7%), and fever (0.2%). The record does not specify a group assignment for these term percentages in the information. Death counts are not reported in the registry record. The listed terms and percentages should therefore be read as descriptive safety information, not as evidence that a particular imaging group caused or prevented an event.
12. What the Result Does, and Does Not, Mean
The registry record describes a randomized comparison of low-dose and standard-dose CT, with non-inferiority for unnecessary appendectomy as the stated objective. It defines the primary outcome and its timeframe, and it records adverse-event counts for both groups. Those details explain what the study set out to examine and provide some descriptive safety information.
However, the primary outcome comparison itself is not reported in the registry record. There are no group-specific event counts, effect estimate, confidence interval, or p-value for negative appendectomy. The non-inferiority margin is also not reported. Without the margin and the estimated contrast with its uncertainty, it is not possible to determine whether the study met its stated objective, how large any difference was, or how precisely that difference was estimated.
This does not mean that the groups were the same, that one group was better, or that the study failed. It means the information needed to make those judgments is not reported in the registry record. Completed status and enrollment of 891 participants do not supply the missing primary-outcome analysis.
The safety counts likewise do not establish a comparative safety effect. They are descriptive counts without a reported statistical comparison, and the term percentages are not assigned to a group in the record. They cannot show causation or settle whether any apparent differences are meaningful.
In general, the distinction between a study’s question and its reported answer is essential. A protocol objective states what investigators intended to evaluate; results and uncertainty estimates are needed to assess what the data indicate. For this trial, the posted information supports a description of the design and outcome definitions, but leaves the central clinical comparison unresolved.
13. Why This Trial Matters Statistically
This trial is statistically notable because its stated objective is non-inferiority. Such a question requires more than observing that one group’s estimate appears close to another’s. In general, the acceptable margin must be defined in advance, and the estimate must be precise enough to rule out differences beyond that margin. The registry record does not report either the margin or the primary-outcome comparison, making the key inferential step unavailable.
The endpoint also illustrates how an outcome definition shapes interpretation. Negative appendectomy is defined as removal of an un-inflamed appendix, and the primary outcome is recorded among participants who underwent non-incidental appendectomy. The analysis population description combines this restriction with intention-to-treat and complete-case language. Since the record does not explain how these elements were implemented, readers cannot fully reconstruct which participants contributed to the primary analysis.
The record’s safety information offers a separate example of the limits of descriptive counts. Serious adverse-event counts and numbers at risk are listed by group, but no uncertainty interval or comparative analysis is reported. Counts can describe what was recorded; without an analysis and relevant detail, they do not establish a treatment effect.
More broadly, the registry highlights why complete reporting matters. A clear endpoint and randomized design describe the framework of a trial, but readers also need the outcome estimates, their precision, and the analysis details to judge the evidence. In the absence of those primary results, the trial’s stated question remains distinct from a statistically supported answer.
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 most important trial-specific limitation of the posted information is that the primary negative appendectomy comparison is not reported in the registry record. Group-specific counts, an effect estimate, a confidence interval, and a p-value are absent. The non-inferiority margin is also not reported, so the criterion for interpreting the stated objective is unavailable.
The registry describes the primary analysis population as participants who underwent non-incidental appendectomy and labels the analysis intention to treat and complete case. It does not explain how those terms were applied together, identify the number analyzed, or report missing outcome data. These gaps make it difficult to understand the population underlying the planned primary comparison.
Important design and analysis details are not reported in the registry record, including who was masked, the randomization and allocation-concealment procedures, the trial’s sample-size justification, the statistical model, multiplicity procedures, and interim analyses. The record lists secondary outcomes but does not provide their results in the information.
Safety reporting is also limited: counts are given, but comparative uncertainty estimates and further event definitions are not. The listed serious adverse-event term percentages are not assigned to a group in the record, and death counts are not reported. These limitations restrict interpretation of both efficacy and safety; they do not establish that the unreported outcomes were favorable or unfavorable.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Diagnosis of Acute Appendicitis: Low-dose Computed Tomography (CT) Versus Standard-dose CT — NCT00913380.
- Registry record last updated 2011-09-12; status last verified 2011-09.
- Results first posted 2011-09-02.
- 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.
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18. Record Summary
NCT00913380 is a completed, randomized, single-masked, parallel-group phase 3 trial sponsored by Seoul National University Bundang Hospital. Enrollment was 891. The study compared low-dose CT with standard-dose CT and stated a non-inferiority objective for unnecessary appendectomy. It started in 2009-09, with primary completion in 2011-04.
The primary outcome was the number of participants with removal of an un-inflamed appendix, assessed 1 week after surgery. The registry describes the primary population as participants who underwent non-incidental appendectomy and the analysis as intention to treat and complete case. Primary-outcome group results and a non-inferiority margin are not reported in the registry record.
The registry lists 12 outcome measures and 0 analyses. It reports serious adverse-event counts of 13 among 444 at risk for low-dose CT and 11 among 447 at risk for standard-dose CT, plus 1 other adverse event in each group. These safety counts are descriptive; a comparative analysis is not reported.