Topical CP-690,550 For Chronic Plaque Psoriasis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Topical CP-690,550 For Chronic Plaque Psoriasis (NCT00678561), a randomized phase 2 study. The primary outcome is Percent Change From Baseline in Target Plaque Severity Score (TPSS) at Week 4.

2. Clinical Question

3. Trial Design

The registry describes NCT00678561 as a completed phase 2 study sponsored by Pfizer. Its title is “Topical CP-690,550 For Chronic Plaque Psoriasis”; the official title characterizes it as a phase 2A randomized, double-blind, vehicle-controlled study assessing safety, toleration, pharmacokinetics, and pilot efficacy. The registry records enrollment of 81 and lists the condition as psoriasis.

Topical CP-690,550 was assessed at 2%, 0.2%, and 0.02%, using once-daily and twice-daily schedules. Placebo vehicle was also listed for both schedules. The brief summary describes application to two psoriasis plaques and one clinic visit each week for 5 weeks. The official title calls the study an intra-individual comparison, whereas the registry’s model field identifies a parallel design. That discrepancy in design description is not explained in the registry record, so the exact relationship between treatment comparisons should not be inferred from those fields alone.

The registry lists a start date of 2008-10-13 and a primary completion date of 2009-07-09, and its status is completed. The primary outcome was percent change from baseline in TPSS at Week 4. Other listed outcomes cover physician assessment of target lesions, TPSS at earlier visits, administration-site adverse events, plasma drug concentrations, and skin biopsy drug concentrations. The record does not report a detailed protocol or a full statistical analysis plan.

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.

Only the first 6 of 8 groups are shown.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Full analysis set (FAS) population included all randomized participants who received at least 1 dose of study medication and had a valid baseline with at least one valid post-baseline value for efficacy parameter. N (number of participants analyzed) is signifying those participants who were evaluable for this measure.

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.

Only the first 6 of 9 groups are shown.

6. Primary Endpoint

The registry lists the primary outcome as Percent Change From Baseline in Target Plaque Severity Score (TPSS) at Week 4, measured over Baseline, Week 4.

The primary endpoint is percent change from baseline in Target Plaque Severity Score (TPSS) at Week 4. Investigators scored target lesions for induration, scaling, and erythema. Each sign used a 5-point scale from 0, none, to 4, very marked; the total TPSS ranged from 0 to 12, with higher scores indicating greater disease severity. For large target lesions, only the treated portion was rated.

A change-from-baseline endpoint describes how the measured score at follow-up differs from the participant’s baseline in relative terms. A negative mean percent change is consistent with a lower score at follow-up relative to baseline; because higher TPSS indicates greater severity, the direction of the score is meaningful to interpretation. The posted results report group means and standard deviations, not individual participant trajectories.

TPSS is used as a measure of target-plaque signs under study. It is not a direct measure of every aspect of psoriasis or of outcomes beyond the target lesions. The registry also lists physician global assessment, earlier TPSS time points, and pharmacokinetic and safety outcomes, but those do not replace the stated primary endpoint. The endpoint’s role is to quantify the measured change in target-plaque severity over the treatment period, while the reported group summaries alone do not determine whether differences between regimens are statistically persuasive.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a continuous measure, and the registry reports its mean and standard deviation within each treatment group. The mean gives the arithmetic average of the observed percent changes in that group. The standard deviation describes how dispersed those observations are around the mean. These summaries answer different questions: the mean indicates the group’s average direction and magnitude, while the standard deviation describes variation among participants.

What does a standard deviation tell the reader?

When observations cluster closely around a mean, the standard deviation is smaller; when observations are more spread out, it is larger. A standard deviation is not itself a confidence interval and does not show the range containing every participant’s result. It also does not tell whether a difference between two group means is compatible with chance variation. That assessment would require an inferential comparison and its uncertainty, neither of which is posted for this endpoint.

The group sizes matter when judging how stable a mean may be. The registry’s analyzed counts range from 4 to 16 across the listed arms. Smaller groups generally yield less precise estimates than larger groups when variability is comparable, but the exact precision cannot be recovered responsibly without the analysis details and an appropriate interval estimate. The posted record contains no confidence intervals for these means. The reported standard deviations and counts are useful descriptive context, not substitutes for uncertainty intervals.

Why is a confidence interval useful?

In general, a confidence interval expresses the uncertainty associated with an estimated quantity under a specified statistical procedure. For a group mean, it can indicate a range of values reasonably compatible with the data and model. For a contrast, it can show both the direction and precision of the estimated difference. A narrow interval indicates greater precision than a wide interval, but precision does not by itself establish clinical importance. No confidence interval for the primary group means or a treatment contrast is reported in the registry record.

Similarly, a p-value is a measure of how compatible data are with a specified null model and assumptions; it is not the probability that a treatment works or that the null hypothesis is true. No p-value is reported for the primary endpoint comparisons. The registry’s count of analyses is 0, and the listed skip reason says values are missing or not estimable for a two-arm comparison of the continuous endpoint. This means the posted summaries should not be treated as an inferential test.

Why can over-dispersion matter?

In general, over-dispersion means that observed variability is greater than a model assumes. When a model underestimates variability, standard errors can be too small and confidence intervals can be too narrow, making apparent evidence look more precise than it is. This is a general statistical concern, not a finding established for this trial. Here, the standard deviations vary among groups, and several are sizable relative to their corresponding group means. The registry does not report a model or analysis that would allow a formal assessment of over-dispersion.

For a continuous endpoint, a comparison might estimate a difference between group means, with uncertainty that depends on the group sizes, variability, design, and chosen method. The record does not provide such an estimate. Further, its official title describes an intra-individual comparison, while its model field says parallel. Paired and independent-group analyses use different information and assumptions. Since the record does not reconcile these design descriptions or report the comparison method, it would be inappropriate to reconstruct a contrast from the arm summaries.

The registry’s sample-size assumption text describes a general planning illustration based on an observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. No planning sample-size results are included in the registry entries, and the description is not evidence that this was the trial’s design calculation. Such an illustration is a planning exercise, not observed power and not a substitute for the study’s actual analysis. The record does not report the trial’s sample-size justification or statistical plan.

Finally, the endpoint is a percent change measure derived from baseline and follow-up scores. The posted means alone do not show baseline values, individual changes, or the distribution’s shape. Without those details, one cannot assess possible influence from unusual observations, baseline imbalance, or departures from analytic assumptions. The sound interpretation is therefore limited to the reported descriptive summaries and the explicit limitations of the registry record.

10. Confidence Intervals for Each Arm

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

R code and output

arm <- c("2% CP-690,550 Once Daily", "0.2% CP-690,550 Once Daily", "0.02% CP-690,550 Once Daily", "Placebo Once Daily", "2% CP-690,550 Twice Daily", "0.2% CP-690,550 Twice Daily")
n   <- c(6, 6, 8, 4, 15, 16)
m   <- c(2.38, -4.76, 2.48, -4.17, -4.46, -1.77)
sp  <- c(5.83, 11.66, 11.5, 8.33, 9.23, 20.87)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  2% CP-690,550 Once Daily  6  2.380  5.830  -3.738  8.498
CARM  0.2% CP-690,550 Once Daily  6  -4.760  11.660  -16.996  7.476
CARM  0.02% CP-690,550 Once Daily  8  2.480  11.500  -7.134  12.094
CARM  Placebo Once Daily  4  -4.170  8.330  -17.425  9.085
CARM  2% CP-690,550 Twice Daily  15  -4.460  9.230  -9.571  0.651
CARM  0.2% CP-690,550 Twice Daily  16  -1.770  20.870  -12.891  9.351

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary endpoint and several secondary outcomes, including physician global assessment, TPSS at Week 1, 2 and 3, administration-site adverse events, plasma concentrations, and skin biopsy concentrations. It reports 5 secondary outcomes and 6 outcome measures. Because multiple outcomes and treatment regimens are listed, a full analysis plan would be important for understanding which comparisons were prespecified and how the risk of false-positive findings was handled. Multiplicity procedures are not reported in the registry record.

The record reports 0 analyses for the posted primary continuous endpoint comparison and gives no p-values or confidence intervals. It therefore does not allow a reader to determine whether any multiplicity adjustment was applied, whether a hierarchy of hypotheses was used, or which analyses were considered confirmatory versus exploratory. The official title describes pilot efficacy, but details of the inferential status of individual outcomes are not reported in the registry record.

The primary endpoint analysis population is described as randomized participants who received at least 1 dose and had a valid baseline and at least one valid post-baseline efficacy value. The record also says that N signifies participants who were evaluable, but the wording in that description is incomplete. It does not report how many randomized participants were excluded from this population, reasons for missing endpoint values, or how missing observations were handled. No imputation method, sensitivity analysis, or missing-data assumption is reported in the registry record.

These omissions matter because the analyzed population depends on having usable follow-up data, and the interpretation of an average change can be affected if missingness is related to outcome or treatment. The group summaries do not establish that missing observations were absent or that their absence had no effect. The registry’s design-field inconsistency also leaves uncertainty about the appropriate comparison structure. These limits preclude reconstructing the analysis or evaluating its robustness from the posted summaries alone.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 2% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports 0 serious adverse events in each listed group. The at-risk counts were 6, 6, 8, and 4 for the once-daily groups in order of 2%, 0.2%, and 0.02% CP-690,550 followed by placebo vehicle. For the twice-daily groups in the same treatment order, the at-risk counts were 17, 17, 15, and 8. These counts describe the groups represented in the adverse-event results, not necessarily the analyzed counts for the primary efficacy endpoint.

The registry also lists participants affected by other adverse events: 4, 2, 5, and 3 in the once-daily groups, and 6, 11, 7, and 4 in the twice-daily groups, using the same regimen order. These are counts, not rates; no percentages should be inferred without an appropriate denominator and definition. The record does not list serious adverse-event terms. Death values are null, so deaths are not reported in the registry record; null should not be read as a confirmed count of zero.

Zero recorded serious adverse events in these groups is a descriptive safety finding for the trial record, not evidence that serious events cannot occur. The registry does not provide a detailed safety analysis, event-level descriptions, or further information needed to judge the completeness of reporting. These figures should be interpreted within the limited study population and follow-up described in the record.

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

The posted primary endpoint results describe mean percent change in TPSS from baseline to Week 4 across topical CP-690,550 and placebo-vehicle regimens. They show both negative and positive group means, with standard deviations indicating variation within groups. The results therefore provide a snapshot of observed target-plaque score changes in the participants included in each endpoint group.

They do not, on their own, establish that CP-690,550 caused a change or that one concentration or schedule differs from placebo vehicle. The registry provides no confidence intervals or p-values for these comparisons, and it reports 0 analyses for the continuous endpoint comparison. The record also does not supply a reconstructed contrast, a prespecified threshold for clinical importance, or details of the statistical plan. Differences between group means should not be treated as evidence of a statistically reliable or clinically meaningful effect.

The study’s purpose is described as pilot efficacy alongside safety, toleration, and pharmacokinetic assessment. Pilot results can be informative about how an endpoint behaved in the studied groups and can motivate further evaluation, but the registry summaries do not resolve whether observed differences would be reproducible. The record’s enrollment of 81 and the smaller analyzed group sizes also underscore that the endpoint summaries represent limited group-level data; no claim about broader populations follows from those counts alone.

The findings are specific to the recorded treatment schedules, target lesions, Week 4 endpoint, and analysis population. They do not establish long-term outcomes, effects on all psoriasis lesions, or outcomes not measured in the registry. Nor do the safety counts prove absence of risk. The registry reports no serious adverse events in the listed groups, but the available information is not a complete characterization of all possible harms or their likelihood.

Accordingly, the strongest interpretation is descriptive: the registry records different mean changes and varying spreads across the listed arms, alongside no posted inferential comparison. Any stronger conclusion would require information that is not reported in the registry record, including the comparison method, uncertainty estimates, missing-data handling, and the prespecified analysis plan.

14. Why This Trial Matters Statistically

This trial is statistically notable because it combines several topical concentrations and dosing schedules with vehicle groups, while reporting a continuous lesion-severity endpoint. That structure makes clear why group means alone are not enough: interpretation depends on the intended comparison, variability, group sizes, and analysis plan. The registry’s official title describes an intra-individual comparison, but its model field says parallel. Those designs imply different ways of relating observations, and the record does not resolve which comparison structure underlies the posted summaries.

The results also illustrate the distinction between descriptive and inferential statistics. Means and standard deviations show the observed average and spread, but without confidence intervals or p-values they do not quantify uncertainty in a treatment contrast. The listed group sizes are modest, and the standard deviations vary across arms. This makes it particularly important not to read small numerical differences between means as decisive evidence.

The record identifies the study as an assessment of pilot efficacy, as well as safety, toleration, and pharmacokinetics. That framing is relevant: the posted data can describe what was observed during the study, but they are not accompanied by the information required to assess confirmatory evidence. Multiplicity handling, sample-size justification, and missing-data procedures are not reported in the registry record.

The trial is also a useful example of how registry data can leave analytical questions unanswered even when endpoint definitions and arm summaries are available. A transparent interpretation distinguishes the measured outcome and reported summaries from conclusions that would require further statistical results. This discipline avoids overstating what descriptive data can support.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record has specific limitations that constrain interpretation. Most importantly, it gives an unresolved design description: the official title calls the study an intra-individual comparison, whereas the model field says parallel. The record does not explain the allocation of lesions or participants across treatment conditions, nor does it specify the analysis method used to account for any within-participant structure. A valid comparison cannot be reconstructed from the arm summaries without that information.

The primary endpoint summaries include means, standard deviations, and analyzed group counts, but no confidence intervals, p-values, or treatment contrasts. The registry reports 0 analyses for the primary continuous endpoint and notes that values are missing or not estimable for a two-arm comparison. Thus, the record does not provide an inferential result that would support a formal comparison between active regimens and vehicle.

The reported efficacy population requires a valid baseline and at least one valid post-baseline value, in addition to randomization and receipt of at least 1 dose. The number and characteristics of participants excluded from this population, reasons for missing outcomes, and missing-data methods are not reported in the registry record. The endpoint population description is also incomplete at its final phrase. These gaps limit assessment of selection and missingness.

The registry does not report the trial’s sample-size justification, a complete statistical analysis plan, multiplicity control, or a clinically important threshold for TPSS. Follow-up for the primary endpoint is at Week 4, and the record does not establish longer-term effects. The endpoint concerns target lesions, with only treated portions rated for large lesions; it does not represent every lesion or every patient-relevant outcome. Finally, the serious-event counts are limited safety summaries, and death values are not reported in the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Topical CP-690,550 For Chronic Plaque Psoriasis — NCT00678561.
• Registry record last updated 2020-12-31; status last verified 2020-12.
• Results first posted 2020-12-31.
• 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.

19. Record Summary

NCT00678561 is a completed phase 2 study of topical CP-690,550 for chronic plaque psoriasis, sponsored by Pfizer. The registry reports enrollment of 81, with treatment schedules using 2%, 0.2%, and 0.02% CP-690,550 once or twice daily and placebo vehicle. The official title describes a randomized, double-blind, vehicle-controlled intra-individual comparison, while the model field identifies a parallel design.

The primary endpoint was percent change from baseline in TPSS at Week 4. The record posts group means, standard deviations, and analyzed counts, but no inferential comparison or confidence intervals. Its analysis population required randomization, at least 1 dose, a valid baseline, and at least one valid post-baseline efficacy value. Missing-data procedures, multiplicity handling, the sample-size justification, and the statistical analysis plan are not reported in the registry record.