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 Visibility of Site Marking for Surgical Time Out With Two Different Skin Preparation Solutions (NCT00739583), a randomized phase 4 study. The primary outcome is Identification of the Random Initials by the Reviewing Orthopaedic Surgeons.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00739583 |
| Phase | Phase 4 |
| Condition | Arthroplasty, Replacement, Hip |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 20 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Johns Hopkins University |
| Results posted | Yes |
2. Clinical Question
Population
Patients undergoing total hip arthroplasty for hip replacement. The registry record describes 20 participants, with 10 randomized to each preparation group.
Intervention
Skin preparation with the chlorhexidine-based solution Chloraprep® (CHG 2% w/v and IPA 70% v/v).
Comparator
Skin preparation with the iodine-based solution Duraprep® (Iodophor 0.7% and IPA 74% w/w).
Primary question
How many randomly assigned initials were correctly identified by reviewing orthopaedic surgeons after the skin preparation, at the time of surgery, approximately 10 minutes after marking?
The registry summary frames the question around whether a skin preparation solution can erase or reduce the visibility of the mark used for surgical site identification. Its stated hypothesis is that chlorhexidine-based preparation erases the marking compared with iodine-based preparation. The mark was described as including the surgeon’s initials, and the primary endpoint counted correctly identified initials as viewed by orthopaedic surgeons.
This is a question about legibility under the study’s assessment conditions. It is not a direct measure of wrong-site surgery, infection, or other clinical outcomes. The registry record also lists secondary questions about change in gray level for a horizontal line and whether reviewing surgeons judged the marking identifiable for site identification. Those outcomes address related aspects of visibility, but they do not change what the primary count measures.
3. Trial Design
The registry record describes a completed, randomized, parallel-group phase 4 study sponsored by Johns Hopkins University. It lists an enrollment of 20 participants and a start of 2008-08, with primary completion in 2009-08. Participants undergoing total hip arthroplasty were assigned to chlorhexidine-based or iodine-based skin preparation, with 10 participants in each group. The record lists masking as none; it does not report which individuals, if any, were aware of assignment during each stage of assessment.
The two preparations were Chloraprep® (CHG 2% w/v and IPA 70% v/v) and Duraprep® (Iodophor 0.7% and IPA 74% w/w). The registry summary says the site marking was performed by the same surgeon in a standardized manner. The endpoint description says each patient was marked with three initials and each mark was viewed by ten surgeons. The assessment was at the time of surgery, approximately 10 minutes after marking.
The design creates a randomized comparison of preparation groups, but the primary outcome record is a count of identified initials rather than a participant-level summary with a reported uncertainty estimate. The registry record does not report the method used to generate the random sequence, allocation concealment, the planned sample-size justification, or a prespecified statistical analysis plan. It also does not report the protocol’s rules for handling incomplete assessments or the analysis population definitions. These omissions limit what can be established about the planning and conduct of the statistical analysis from the registry record alone.
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
| Stage | Chlorhexidine Group | Iodine Group |
|---|---|---|
| STARTED | 10 | 10 |
| COMPLETED | 10 | 10 |
| NOT COMPLETED | 0 | 0 |
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 | Chlorhexidine Group | Iodine Group | Total |
|---|---|---|---|---|
| Participants analysed | 10 | 10 | 20 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 4 | 3 | 7 |
| Age, Categorical: >=65 years | Participants | 6 | 7 | 13 |
| Age Continuous | years | 71 (SD 4.6) | 73 (SD 4.2) | 72 (SD 4.5) |
| Sex: Female, Male: Female | Participants | 3 | 6 | 9 |
| Sex: Female, Male: Male | Participants | 7 | 4 | 11 |
| Region of Enrollment: United States | participants | 10 | 10 | 20 |
6. Primary Endpoint
The registry lists the primary outcome as Identification of the Random Initials by the Reviewing Orthopaedic Surgeons, measured over at time of surgery, approximately 10 minutes.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | number of correctly identified initals |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the number of randomly assigned initials that reviewing orthopaedic surgeons correctly identified. It is recorded as a count. The registry description says that each patient was marked with three initials and each was viewed by ten surgeons, giving a total of 300 initials for each group. The stated assessment time was at surgery, approximately 10 minutes after marking.
The measure is intended to capture whether the site marking remained readable after skin preparation. This makes it relevant to the study’s visibility question: a mark that reviewers can identify may be easier to use for site identification than one they cannot identify. However, the endpoint is not itself a count of patients with an identifiable mark, nor does it directly measure wrong-site procedures or infection. The record does not explain how disagreements among reviewers were handled, how repeated views were combined, or whether a particular threshold defined an acceptable level of visibility.
The posted primary values are 209.0 for the Chlorhexidine Group and 296.0 for the Iodine Group. The registry record does not provide a confidence interval or a sponsor-reported inferential comparison for this count. The values therefore describe the recorded number of correctly identified initials in each group, but they do not, on their own, quantify the precision of a between-group effect.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The primary outcome is reported as 209.0 correctly identified initials in the Chlorhexidine Group and 296.0 in the Iodine Group. The record describes 300 initials for each group. These counts show the observed pattern in the assessments: fewer initials were correctly identified in the chlorhexidine group than in the iodine group. The registry record does not report an inferential comparison for the primary count, and the posted statistical output marks a two-arm comparison as not estimable for this count-type endpoint. No primary-endpoint confidence interval or p-value is reported. The counts should therefore be read descriptively, without treating them as a complete estimate of the uncertainty in a group difference.
There is an important distinction between the number of participants and the number of viewed initials. The study enrolled 20 participants, with 10 in each group, while the endpoint description reports 300 initials per group because marks were viewed by multiple surgeons. Those repeated assessments do not represent 300 independent participants per group. General statistical reasoning indicates that observations clustered within patients or reviewers can be correlated; an analysis that treats every view as independent could understate uncertainty. The registry record does not report how this dependence was handled.
A secondary continuous outcome, mean change in gray level (contrast) of the horizontal line, has a recalculated unadjusted comparison. The Chlorhexidine Group mean was 59.8 (standard deviation 59.8), and the Iodine Group mean was 14.9 (standard deviation 11.4). The recalculated mean difference, expressed as Iodine Group minus Chlorhexidine Group, was -44.9, with a 95% confidence interval from -82.63 to -7.169 and p = 0.02. This is an unadjusted re-calculation from the posted summary statistics, not a sponsor-reported analysis. The interval indicates uncertainty around the estimated difference; it excludes zero, but its breadth also shows that the plausible magnitude is not pinned down precisely.
That secondary result concerns gray-level contrast, not the primary count of correctly identified initials. It can provide supporting context about a visual property of the marking, but it is not a substitute for a reported primary comparison. The registry record lists another secondary outcome—surgeons’ judgment that the marking was identifiable—but gives no result for it. The overall evidence in the registry is therefore incomplete: the primary endpoint is descriptive, one secondary endpoint has an unadjusted recalculation, and another secondary outcome has no posted result. Neither the primary counts nor the secondary result should be interpreted as evidence about clinical outcomes not measured by these endpoints.
9. Statistical Methods Explained
The registry lists a randomized parallel-group design, with a chlorhexidine-based preparation compared with an iodine-based preparation. Random assignment is intended, in general, to make treatment groups comparable on average, including for factors that are not measured. It does not ensure balance in a small study, and it cannot by itself resolve problems in outcome measurement or analysis. The record does not report the random-sequence method or allocation concealment, so those details cannot be assessed.
What does the primary count tell us?
A count records how many events or items meet a definition. Here, the counted items are initials correctly identified by reviewing surgeons. A count can be useful for describing the observed assessments, but a between-group inference also needs a defined analysis and an estimate of uncertainty. The registry record provides the group counts but no sponsor-reported comparison, confidence interval, or p-value for the primary outcome. The posted analysis information indicates that a two-arm comparison was not estimable for this count-type endpoint. It is therefore not appropriate to infer a statistically tested difference from the counts alone.
There are also multiple levels in the assessment: participants were marked, each mark included initials, and surgeons viewed those initials. General statistical methods distinguish independent observations from repeated or clustered observations. When measurements from the same person or reviewer are related, their shared context can make them more alike than observations from unrelated people. Ignoring that correlation can make standard errors too small and confidence intervals too narrow. A suitable analysis might account for clustering, but the registry record does not report which model or method was used, or whether clustering was addressed.
How should the secondary mean comparison be read?
The gray-level outcome is reported as a mean and standard deviation for each group. The recalculated difference is -44.9, calculated as the Iodine Group mean minus the Chlorhexidine Group mean. The corresponding 95% confidence interval runs from -82.63 to -7.169, with an unadjusted p-value of 0.02. These are simple, unadjusted recalculations from the posted summary statistics; the registry record does not list sponsor-reported analyses for this outcome.
In general, a confidence interval gives a range of values compatible with the observed data under the assumptions of the analysis. Its width conveys precision: wider intervals leave more uncertainty about the underlying difference. A p-value describes how unusual data at least as incompatible with a null hypothesis would be under that hypothesis and the model assumptions; it is not the probability that the null hypothesis is true. Neither quantity addresses bias from study conduct, outcome definition, or model misspecification. In particular, the recalculated comparison does not account for multiple secondary outcomes or possible dependence among measurements unless the underlying analysis explicitly does so; such adjustment is not reported in the registry record.
The standard deviations indicate spread among measurements within each group. They are not standard errors and should not be read as confidence intervals. A standard error describes the estimated precision of a statistic, while a standard deviation describes variation in the observations. General methods also note that unequal variability between groups can affect the appropriateness of a pooled-variance comparison. The recalculation reports a pooled standard deviation of 43.05, but the registry record does not report a sponsor analysis or detailed modeling assumptions for the secondary comparison.
What do the planning illustrations mean?
The planning calculations are illustrations based on fractions of the observed secondary effect. They assume a two-sided significance level of 0.05, equal allocation, and a normal approximation. For the observed effect, the illustration gives 15 participants per arm for 80% power and 20 participants per arm for 90% power; for planning at 75% of the observed effect, it gives 26 and 35 participants per arm; and for planning at 50% of the observed effect, it gives 58 and 78 participants per arm. These figures are planning illustrations, not observed power, and they do not establish the study’s original sample-size rationale. That rationale is not reported in the registry record. The illustrations also concern the observed secondary mean effect; they are not a planning analysis for the primary count endpoint.
More generally, power is a design-stage probability of detecting a specified effect under stated assumptions. It is not a measure of how likely a result is to be true after the study, nor is it a property that can be recovered from the observed result alone. Because the study’s original assumptions and primary-endpoint analysis plan are not reported, the planning illustration should not be used to claim that the trial was adequately or inadequately powered for its primary question.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary outcome and two secondary outcomes, but the statistical analysis plan is not reported in the registry record. In particular, the record does not report whether there was a prespecified hierarchy among outcomes, whether any adjustment for multiple testing was planned, or whether interim analyses were conducted. These points cannot be inferred from the posted outcome summaries.
Multiplicity matters because testing several outcomes can increase the chance of a result that appears unusual under a null hypothesis. This general concern is relevant to the secondary mean comparison, whose recalculated p-value is unadjusted. The record does not report a multiplicity adjustment, so that p-value should not be read as if it accounted for the full set of outcomes. The primary endpoint also lacks a reported inferential comparison, meaning the registry does not offer a complete primary-versus-secondary analysis framework.
Missing-data handling is not reported in the registry record. The record does not state whether all randomized participants contributed all planned assessments, whether any measurements were unavailable, or how incomplete assessments were handled. A blank or unreported result is not evidence that there were no missing observations; it means the registry record does not describe them.
Analysis populations are also not reported. The record does not say whether analyses followed the randomized assignment regardless of treatment received, were limited to participants who completed assessments, or used another definition. Details of the randomization procedure and any protocol deviations are not reported either. These omissions limit assessment of whether the reported summaries preserve the advantages of randomization or reflect a selected set of observations.
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 |
|---|---|---|---|
| Chlorhexidine Group | 0 | 10 | 0.0% |
| Iodine Group | 0 | 10 | 0.0% |
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 |
|---|---|
| Chlorhexidine Group | 0 of 10 |
| Iodine Group | 0 of 10 |
The registry reports zero serious adverse events and zero other adverse events in the Chlorhexidine Group and zero serious adverse events and zero other adverse events in the Iodine Group. Each group is listed with 10 participants at risk for the serious and other adverse-event summaries. The deaths field is not reported in the registry record.
These figures describe what was recorded for the study’s safety summaries. They do not establish that an event could not occur, or that the two preparations have identical safety profiles. With 10 participants in each group, the record’s absence of reported events provides limited information about uncommon outcomes or risks that might occur outside the study’s observation period. The registry record does not provide further detail on event definitions, collection procedures, or the duration of safety follow-up, so those aspects cannot be assessed from these figures.
The study’s primary question concerns visibility of site markings, not a comparative evaluation of safety. The adverse-event counts should therefore be read separately from the visibility outcomes and not as a substitute for a broader safety assessment.
12. What the Result Does, and Does Not, Mean
The posted results describe how the skin markings were assessed in this randomized study and report the number of initials correctly identified in each preparation group. The primary counts are 209.0 for the Chlorhexidine Group and 296.0 for the Iodine Group, against the record’s description of 300 initials per group. This is an observed difference in the recorded counts, but the registry record does not provide an inferential comparison or a confidence interval for the primary endpoint. The precision of a primary between-group effect is therefore not quantified in the record.
The recalculated secondary mean comparison reports a difference in gray-level contrast, with an unadjusted confidence interval and p-value. That result can inform interpretation of the contrast measure, but it is not the primary count and does not directly measure correct identification, wrong-site procedures, or infection. The registry record also lists a surgeon-judgment outcome without a posted result. Taken together, the available outcome information is partial and does not support treating one secondary measure as a replacement for missing primary inference.
General statistical interpretation also depends on the structure of the observations. Multiple surgeons viewed marks from participants, so the number of views does not equal the number of independent participants. The record does not explain how repeated assessments or reviewer differences were handled. Without that information, the uncertainty around the count comparison cannot be reconstructed from the posted primary summaries.
The findings do not establish whether either preparation changes clinical outcomes or the incidence of wrong-site surgery. Those outcomes are not reported as measured results in this record. Nor do the data establish that a visible marking is sufficient for safe site identification; the study’s endpoints concern identification and visual characteristics under its assessment conditions. The results should be understood as descriptive evidence about marking visibility in this small randomized study, with important gaps in reported analysis and uncertainty.
13. Why This Trial Matters Statistically
This study illustrates why an endpoint’s measurement structure matters as much as the number printed beside it. A primary count can look straightforward, but the registry description includes multiple marks and multiple surgeon assessments for each participant. Those views are not automatically independent observations. Statistical methods need to reflect how observations are clustered if the aim is to estimate uncertainty reliably.
It also demonstrates the difference between a descriptive outcome and an inferential comparison. The registry posts group counts for the primary endpoint, but not a primary confidence interval or sponsor-reported test. The observed pattern is visible in the counts, yet the record does not show how precise a group-level difference might be. A complete interpretation needs both an effect estimate and a defensible account of its uncertainty, with methods suited to the outcome and design.
The secondary gray-level outcome provides a separate example: a recalculated mean difference, confidence interval, and unadjusted p-value can be presented, but those statistics do not solve the primary endpoint’s analysis gap. Nor do they answer how multiple outcomes were handled. The registry record does not report the statistical plan, outcome hierarchy, missing-data approach, or analysis populations, making it difficult to assess how the reported results relate to the original plan.
These are broadly useful lessons for clinical research: distinguish participant counts from repeated measurements, separate primary from secondary evidence, and treat unadjusted exploratory results cautiously. Here, those issues are especially relevant because the measurement process involves surgeon judgments and repeated views, while the posted primary result is a count without a reported inferential analysis.
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.
Several limitations specific to this study constrain interpretation. The registry record describes 20 participants, with 10 in each group. The primary endpoint counts initials viewed by surgeons, but the record does not report the statistical method used to account for repeated assessments within participants or differences among reviewers. The number of views should not be treated as the number of independent participants.
The primary outcome has no reported confidence interval or sponsor-reported comparison. This leaves the uncertainty around the group contrast unquantified. The secondary gray-level comparison is a recalculation from posted summaries and is unadjusted; it should not be treated as a prespecified sponsor analysis. The registry does not report a result for the other listed secondary outcome, the surgeons’ judgment of identifiability.
Masking is listed as none. The record does not specify which study personnel or assessors knew group assignment, so the potential influence of awareness on a subjective assessment cannot be evaluated. The record also does not report the randomization method, concealment, participant flow, missing-data handling, analysis populations, protocol deviations, or the original sample-size rationale. The statistical analysis plan and multiplicity approach are not reported.
Finally, the recorded endpoints concern visibility and identification under the described assessment conditions. The registry record does not provide evidence about wrong-site surgery or infection as study outcomes. The safety summary reports no serious or other adverse events, but further safety-collection details and death counts are not reported. These limitations restrict conclusions to the posted visibility summaries and their stated assessment context.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Visibility of Site Marking for Surgical Time Out With Two Different Skin Preparation Solutions — NCT00739583.
- Registry record last updated 2013-07-10; status last verified 2013-06.
- Results first posted 2013-07-10.
- 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
NCT00739583 is a completed, randomized, parallel-group phase 4 study sponsored by Johns Hopkins University. It enrolled 20 participants undergoing total hip arthroplasty, with 10 assigned to chlorhexidine-based preparation and 10 to iodine-based preparation. The record lists a start of 2008-08 and primary completion in 2009-08, with no masking.
The primary outcome was the number of initials correctly identified by reviewing orthopaedic surgeons at surgery, approximately 10 minutes after marking. The posted group counts are 209.0 for the Chlorhexidine Group and 296.0 for the Iodine Group. The registry record does not report an inferential comparison for this primary count. A secondary gray-level contrast outcome has a recalculated unadjusted mean comparison; a result for the other listed secondary outcome is not reported in the registry record.
The record reports zero serious and zero other adverse events in each group. Deaths are not reported in the registry record. Details of the analysis plan, missing-data handling, analysis populations, and multiplicity approach are not reported.