N-Acetyl Cysteine in Pathologic Skin Picking: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for N-Acetyl Cysteine in Pathologic Skin Picking (NCT01063348), a randomized phase 2 study. The primary outcome is Yale Brown Obsessive Compulsive Scale (YBOCS) Modified for PSP (NE-YBOCS).

2. Clinical Question

The official title describes a double-blind, placebo-controlled study. The registry also identifies the study as randomized, triple masked, and parallel. The clinical question is therefore framed as a comparison between two assigned treatment groups, with the NE-YBOCS as the primary measure and repeated assessments over the study period.

The registry describes an enrollment of 66. Its brief summary, which describes the proposed study, says thirty subjects would receive 12 weeks of double-blind treatment with N-acetyl cysteine or matching placebo. These are different enrollment figures in the record, and the registry does not explain their relationship. Neither figure indicates how many participants contributed data to a particular efficacy analysis.

The stated hypothesis was that N-acetyl cysteine would be more effective than placebo for pathologic skin picking. A hypothesis is a question to test, not a finding. With no efficacy estimates or comparisons reported, the registry record cannot establish whether the groups differed on the primary measure or how precisely any difference was estimated.

3. Trial Design

This phase 2 study is listed as randomized, triple masked, and parallel, with placebo as the comparator. The official title describes it as double-blind and placebo-controlled, while the registry’s design fields identify triple masking. Both descriptions indicate masking, but the record does not explain which people were masked or how the difference in masking descriptions should be understood. The sponsor is the University of Chicago.

The registry lists enrollment as 66 and the study status as completed. The start date is 2012-09, and primary completion is listed as 2015-07. The brief summary describes a proposed study of thirty subjects and 12 weeks of double-blind treatment. The record does not reconcile this proposed enrollment with the enrollment figure recorded for the study. These figures should not be treated as interchangeable measures of the number analyzed.

The intervention was N-acetyl cysteine in 600mg tablets taken by mouth, with a stated daily dose range of 1200mg to 3000mg. The comparison group received matching placebo daily. The entire study for an individual participant was described as lasting 12 weeks. The NE-YBOCS was scheduled once every three weeks during that period.

The registry names the Skin Picking Self Assessment Scale (SP-SAS) as a secondary outcome and reports two outcome measures. It does not report the results of either measure. No analysis results are listed, and no specific analysis population, statistical model, or treatment of missing observations is described in the registry record.

The trial’s design supports a planned comparison of assigned groups, but the design alone does not show what the observed outcomes were. Randomization and masking describe features of how a study is organized; they do not replace reported results or details about how those results were analyzed.

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:

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 Yale Brown Obsessive Compulsive Scale (YBOCS) Modified for PSP (NE-YBOCS), measured over Once every three weeks during the 12 week study for each subject.

The primary endpoint is the Yale Brown Obsessive Compulsive Scale modified for pathologic skin picking, identified as the NE-YBOCS. It measures skin-picking severity in units on a scale, with the total formed from an urges subscale and a behaviors subscale. The registry says the minimum total score is 0 and the maximum is 40, and that higher scores indicate more severe skin picking. Each subscale ranges from 0 to 20.

Participants were to complete the measure once every three weeks during the 12-week study, with the outcome assessed at each visit. Repeated assessments can describe how scores change over time, rather than relying on a single measurement. In general, a scale that directly measures the condition of interest can offer a structured way to compare participants’ reported symptoms across treatment groups. That is the intended role of this endpoint; the record does not report its observed scores or a comparison between groups.

The registry specifies a mean as the summary measure and standard deviation as the measure of dispersion. In general, a mean describes the group’s average score, while a standard deviation describes how spread out individual scores are around that average. Neither statistic alone shows the uncertainty in a treatment-group comparison. The registry record does not provide the mean scores, standard deviations, confidence intervals, or an estimate of the difference between groups.

Because the endpoint was assessed at multiple visits, interpretation would depend on which visit or pattern of change was analyzed. The record’s stated reason for not reducing the primary outcome to one comparison is that it has several categories or time points. The endpoint’s measurement schedule is reported, but a single primary time-point comparison is not.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a continuous primary outcome summarized using a mean and standard deviation. The NE-YBOCS total is a numerical score, and the record indicates that higher values correspond to more severe skin picking. In general, a mean gives a group’s average score, while a standard deviation indicates the degree of variability among individual scores. The mean and standard deviation describe the data; they do not by themselves quantify the uncertainty of a comparison between groups.

What does randomization contribute?

In general, random allocation is intended to make treatment groups comparable at the outset by assigning participants through a chance-based process. This can reduce systematic differences between groups, though it does not guarantee identical groups in every characteristic. Randomization is part of the design reported for this study. The registry record does not describe the sequence-generation method, how assignments were concealed, or whether any departures from assigned treatment occurred.

What does masking mean for interpretation?

The official title calls the study double-blind, and the registry design information calls it triple masked. Masking is intended to limit the influence of expectations on behavior, outcome reporting, or assessment. The record does not specify which people were masked, how masking was maintained, or why the two descriptions differ. The design labels alone cannot show whether masking remained effective throughout the study.

Why does the repeated schedule matter?

The NE-YBOCS was scheduled once every three weeks during the 12-week study. In general, repeated observations from one participant are related to each other; they are not equivalent to observations from separate participants. An analysis of repeated measures should account for that dependence. An analysis might focus on a single visit, a change from an earlier measurement, or an overall trajectory. These approaches answer different questions and can use the repeated data differently. The registry record does not identify which approach was planned or used.

The record says the primary outcome has several categories or time points and was not reduced to one comparison. Thus, the timing or structure of a single primary contrast is not stated. Without a specified contrast and reported estimates, readers cannot determine which visit or overall pattern would represent the principal efficacy result. No statistical model, covariate adjustment, or analysis method for the primary endpoint is reported in the registry record.

How should uncertainty be assessed?

In general, a confidence interval presents uncertainty around an estimated quantity, such as a mean difference between groups. A narrow interval indicates greater precision than a wide interval, given the analysis assumptions. A p-value addresses how compatible the data are with a specified null hypothesis under an analysis model; it is not a measure of the size or clinical importance of an effect. Neither confidence intervals nor p-values for the efficacy comparison are reported in the registry record.

The registry’s stated outcome summary is a mean with standard deviation. If a treatment comparison were reported, readers would also need to know the contrast being estimated, the analysis population, and how repeated observations and missing measurements were handled. The record does not report these details. It also does not state whether the analysis was adjusted for other variables.

What do the planning assumptions mean?

The registry describes planning illustrations based on a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is defined as a stated fraction of the observed effect. These are assumptions for a planning calculation, not reported features of the trial’s completed efficacy analysis. Sample-size calculations are intended to illustrate how design requirements depend on assumptions about the effect and variability. They are not observed power and do not establish that a completed study did or did not detect an effect.

In general, over-dispersion means that observed variability exceeds what a statistical model assumes. When that occurs, uncertainty may be understated if the model does not account for the extra variability. This is a general statistical consideration, not a reported finding about this trial. The registry record does not report a model or dispersion assessment for the NE-YBOCS.

The record lists no analysis results. It therefore does not provide a basis for independently checking an efficacy estimate against summary statistics. Any planning illustration should be understood in its stated role as a design calculation, rather than as a substitute for an analysis of participant outcomes.

10. Multiplicity, Missing Data and Analysis Populations

The primary endpoint was scheduled for repeated assessment once every three weeks during the 12-week study, and the registry indicates that the primary outcome has several categories or time points. When a study considers several time points, outcomes, or comparisons, the chance of a false-positive finding can increase if each is tested separately without an appropriate plan. In general, multiplicity procedures can control or describe this issue. The statistical plan for multiplicity, including any adjustment or prespecified hierarchy, is not reported in the registry record.

The record names the SP-SAS as a secondary outcome and reports two outcome measures. It does not state how the primary and secondary measures were prioritized in analysis, whether secondary outcomes were exploratory, or whether any multiplicity adjustment was planned. No analysis results are reported for these measures.

Missing data can affect repeated-measures analyses if participants miss visits or withdraw, particularly when missingness is related to symptoms or treatment. In general, an analysis should state how missing measurements are handled and what assumptions that approach makes. The registry record does not report the amount or pattern of missing outcome data, the reasons for missingness, an imputation method, or a sensitivity analysis.

The analysis populations are also not reported. The record does not say whether an efficacy analysis included all randomized participants, only participants who completed treatment, or another defined group. The enrollment figure and the adverse-event at-risk counts do not establish the size of an efficacy analysis population. Interim analyses and stopping rules are not reported in the registry record.

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 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists serious adverse events separately from other adverse events. For N-acetyl cysteine, serious adverse events are recorded for 0 participants among 35 at risk; for placebo, the figure is 0 among 31 at risk. The record does not list serious adverse-event terms. The death fields are not reported in the registry record, so they should not be read as zero deaths.

For other adverse events, the registry records 9 affected participants among 35 at risk in the N-acetyl cysteine group and 1 among 31 at risk in the placebo group. These are counts from the posted safety record. They do not show the timing, severity, duration, or specific nature of the other events. The registry record also does not establish whether each event was considered related to treatment.

In general, adverse-event counts describe events observed and recorded during a study; a difference in counts does not by itself establish that treatment caused the difference. Interpretation depends on how events were defined, collected, and followed, as well as the amount of exposure and the analysis plan. Those details are not reported in the registry record. The figures should therefore be read as descriptive safety information, not as a complete assessment of comparative risk.

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

The record identifies a completed, randomized, placebo-controlled phase 2 study of N-acetyl cysteine for pathologic skin picking and specifies the intended primary measure. It also describes the treatment period and repeated assessment schedule. These details establish what the study was designed to investigate, but they do not provide the efficacy findings.

The registry record does not report NE-YBOCS results, a treatment-group comparison, or an estimate with a confidence interval. It therefore does not show whether the groups differed, the direction or size of any difference, or the precision of an estimate. The hypothesis in the brief summary should not be mistaken for a conclusion.

The record reports adverse-event counts for both groups. Those descriptive counts do not demonstrate that treatment caused or prevented events, and the death figures are not reported in the registry record. No comprehensive conclusion about safety can be drawn from the counts alone.

In general, the interpretation of a clinical trial depends on the outcome definition, the analysis plan, the participants included, and the completeness of follow-up. For this study, the registry does not report the efficacy analysis, the handling of missing observations, the analysis populations, or the statistical methods used for repeated outcomes. These omissions limit what can be concluded from the posted record.

The study’s completed status does not mean that its results are available in the registry record. Likewise, a planned sample-size illustration is not evidence that an effect was observed or that a particular level of power was achieved. The appropriate reading is narrow: the record describes the trial design and some safety counts, while leaving the primary efficacy question unanswered in the posted results.

13. Why This Trial Matters Statistically

This trial raises a central statistical issue in studies that measure symptoms repeatedly: a clear comparison requires a defined outcome contrast. The NE-YBOCS was scheduled once every three weeks during a 12-week period, so the results could be described by visit or through a pattern across visits. Those summaries do not necessarily answer the same question. The registry indicates that the primary outcome has several categories or time points and was not reduced to one comparison.

The distinction between a planned question and an analyzed result is important. The brief summary states a hypothesis about N-acetyl cysteine compared with placebo, while the registry record does not report an efficacy estimate or analysis. Without the estimate and its uncertainty, readers cannot assess the magnitude, direction, or precision of a treatment-group difference.

The record also illustrates why enrollment and analysis sample size should not be treated as equivalent. Enrollment is listed as 66, while the brief summary describes thirty subjects in the proposed study. The record does not explain the difference or state how many participants contributed primary outcome data. Clear reporting of the analysis population and missing observations is essential when outcomes are collected repeatedly.

Finally, descriptive safety counts and planning calculations serve distinct purposes. The adverse-event figures describe recorded events, while sample-size illustrations depend on assumptions and are not observed power. Keeping these forms of information separate helps prevent design details from being mistaken for evidence about treatment effects. In this registry record, the design is described more fully than the efficacy findings.

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 limitation of the registry record for interpreting efficacy is that it does not report outcome results or analyses. No primary endpoint means, standard deviations, group comparison, confidence interval, or p-value are reported. The record also indicates that the primary outcome involves several categories or time points, without specifying a single comparison for interpretation.

The enrollment descriptions are not reconciled: the registry lists 66 enrolled, whereas the brief summary describes thirty subjects in the proposed study. The record does not explain whether these figures refer to different stages or populations. It also does not report the number randomized, treated, completing follow-up, or included in an efficacy analysis.

Important analysis details are absent from the registry record, including the statistical model, the analysis population, the approach to missing measurements, and any adjustment for multiple outcomes or time points. The record does not report participant characteristics or further eligibility details, limiting assessment of how the study population relates to the broader group described by the condition.

The safety record gives counts but does not describe event terms, timing, severity, relatedness, or the death figures. The descriptions of masking differ between the official title and the registry design information, and the record does not clarify the difference. These limitations concern what can be learned from the registry record; they do not establish that the information was absent from other study materials.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: N-Acetyl Cysteine in Pathologic Skin Picking — NCT01063348.
• Registry record last updated 2023-02-23; status last verified 2023-02.
• Results first posted 2016-10-31.
• 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

NCT01063348 is a completed phase 2 study sponsored by the University of Chicago. The registry describes it as randomized, triple masked, and parallel; the official title calls it double-blind and placebo-controlled. The listed enrollment is 66, with a start date of 2012-09 and primary completion of 2015-07.

The comparison was N-acetyl cysteine, given as 600mg tablets by mouth at a stated daily dose range of 1200mg to 3000mg, versus matching placebo taken daily. The primary measure was the NE-YBOCS, assessed once every three weeks during the 12-week study. The SP-SAS is listed as a secondary outcome.

The registry record does not report efficacy analyses or results. It lists serious adverse events for 0 of 35 at risk in the N-acetyl cysteine group and 0 of 31 at risk in the placebo group; other adverse events are listed for 9 of 35 and 1 of 31, respectively. Death figures are not reported in the registry record.