Priapism in Boys and Men With Sickle Cell Disease - Demographics, Characteristics and Prevalence: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Priapism in Boys and Men With Sickle Cell Disease - Demographics, Characteristics and Prevalence (NCT00300235), a registered phase not stated study. The primary outcome is Enumeration of the Prevalence of Priapism in Males With Sickle Cell Anemia and Sickle Beta Zero Thalassemia..

2. Clinical Question

3. Trial Design

This is an epidemiologic, interview-based study, not a randomized treatment trial. Its stated purpose was to collect demographic and clinical information about priapism among people with sickle cell disease. The registry lists an enrollment of 1464 and a status of completed. The recorded study start is 2005-08, and primary completion is recorded as 2008-03.

The registry describes five groups. Four consist of people with HbSS/HbSβ0 diagnoses, divided into age ranges 5 to 9.9 years, 10 to 14.9 years, 15 to 24.9 years, and over 25 years. The fifth is described as people aged 15 and older with HbSC or HbSβ+ diagnoses. The group descriptions list 200, 400, 400, 400, and 250 subjects, respectively. These are descriptions in the registry, not evidence of treatment allocation.

The primary population is described as all participants who completed the survey. The primary outcome concerns males with sickle cell anemia and sickle beta zero thalassemia; the registry does not explain how survey completion or eligibility was determined in practice. The group categories permit descriptive organization by age and diagnosis, but they do not constitute randomized arms or a like-for-like control comparison. How participants were recruited, where interviews took place, and whether any additional eligibility criteria applied are not reported in the registry record.

Secondary aims included describing episode timing, duration, frequency, associated activities, treatments used, and treatment outcomes; making a descriptive prevalence comparison with older patients who had other sickle hemoglobinopathies; and assessing patient and parent understanding of priapism. The posted record does not give detailed methods or results for these aims.

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

Analysis population for the primary outcome, as defined in the registry: All particpants who completed survey were analyzed.

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 Enumeration of the Prevalence of Priapism in Males With Sickle Cell Anemia and Sickle Beta Zero Thalassemia., measured over At time of interview.

The primary endpoint is an enumeration of participants with a history of priapism. A participant was counted as having the outcome if the survey response to “Have you ever had priapism?” was yes. The registry specifies reporting by diagnosis and age group, with assessment at the time of interview.

This measure captures a reported lifetime history up to the interview, rather than newly occurring episodes during a defined observation period. It therefore addresses how many surveyed participants reported ever experiencing priapism, not how often episodes occurred during follow-up. The registry describes the primary outcome as a number of participants, so the intended result is a count. A count needs its population denominator and group definition to be interpretable; the registry separately states that all participants who completed the survey were analyzed.

In general, lifetime-history questions can summarize the burden participants report, while depending on recall and understanding of the question. A response of yes does not, by itself, describe when an episode occurred, how many episodes occurred, or their duration or severity. Those characteristics were among the secondary topics, but their detailed results are not reported in the registry record. The primary endpoint is useful for the stated descriptive question, but it does not establish an incidence rate, a causal association, or an effect of treatment.

The registry record does not report the primary endpoint counts or prevalence estimates. It also does not report confidence intervals for those estimates, so the precision of the primary result cannot be assessed from the posted record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The study’s primary analysis is descriptive. It asks for a count of participants reporting a prior experience, organized by age and diagnosis. This differs from an analysis comparing randomized treatments: participants were not assigned to treatments, and the listed categories are demographic and diagnostic groups. The registry does not report a randomized allocation or a like-for-like control comparison.

What does a count mean?

A count is the number of people meeting the outcome definition. In this study, the definition is a yes response to the lifetime-history question. A count alone is tied to the size of the group from which it came. For prevalence, readers generally need both the number reporting the outcome and the number assessed in the relevant group, so the result can be understood as a proportion of that group. The registry record does not report the primary counts or the prevalence estimates.

In general, prevalence describes the share of a population with a condition or history at a specified assessment point. A lifetime question is broader than a question about current symptoms or episodes within a defined follow-up period. It can include events from different points in a participant’s past, but depends on recollection and interpretation of the survey wording. It cannot be treated as an incidence rate, which concerns new events over time.

Why separate by age and diagnosis?

Reporting separately by age and diagnosis can make descriptive patterns visible and can avoid treating clinically distinct groups as interchangeable. The registry defines four age categories for participants with HbSS/HbSβ0 and an additional older group with HbSC or HbSβ+. These categories are not randomized arms. Differences in their outcome counts, if reported, could reflect differences in age, diagnosis, recruitment, or other characteristics; a simple descriptive contrast cannot establish why groups differ.

In general, adjustment for measured characteristics can help account for some differences between groups, but it cannot automatically remove bias from unmeasured characteristics or weak study design. The registry record does not report a model, covariate adjustment, or a statistical test for the primary outcome. It does not report confidence intervals either. Without an estimate and its uncertainty, neither the scale nor the precision of the primary finding can be evaluated.

How should planning illustrations be understood?

The sample-size illustrations use an effect based on the observed effect, a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They are planning illustrations, not evidence of the study’s original design or of observed power. The registry does not report the study’s own sample-size justification. Because this is not a randomized comparison and the groups are not like-for-like control arms, a two-arm planning framework does not describe the primary descriptive question particularly well. No numerical planning outputs are.

In general, sample-size planning estimates how much information a future study might need under stated assumptions. Such an illustration does not show that the study had a given probability of detecting an effect after data collection, and it cannot replace a confidence interval around the observed result. If assumptions are poorly matched to the design or endpoint, the illustration may not be useful for judging the study’s descriptive precision.

What is not available for statistical appraisal?

The registry defines the primary outcome but does not report its counts, prevalence estimates, uncertainty, or analysis details. It also does not describe how the survey was validated, how responses were checked, or how unclear answers were handled. The basic interpretation therefore remains descriptive: a survey response was intended to identify participants reporting ever having had priapism, with findings organized by age and diagnosis. The numeric result needed to quantify that outcome is not reported in the registry record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Age 5-9.9 HbSS/HbSβ0", "Age 10-14.9 HbSS/HbSβ0", "Age 15-24.9 HbSS/HbSβ0", "Age >25 HbSS/HbSβ0", "Age >15 HbSC/HbSβ+")
n      <- c(208, 240, 398, 362, 251)
events <- c(18, 58, 160, 189, 60)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Age 5-9.9 HbSS/HbSβ0  208  18  8.7  5.2  13.3  5.5  13.3  5.6  13.3
ARM  Age 10-14.9 HbSS/HbSβ0  240  58  24.2  18.9  30.1  19.2  30.0  19.2  30.0
ARM  Age 15-24.9 HbSS/HbSβ0  398  160  40.2  35.3  45.2  35.5  45.1  35.5  45.1
ARM  Age >25 HbSS/HbSβ0  362  189  52.2  46.9  57.5  47.1  57.3  47.1  57.3
ARM  Age >15 HbSC/HbSβ+  251  60  23.9  18.8  29.7  19.0  29.5  19.1  29.6

11. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome and secondary objectives concerning episode characteristics, comparison with other sickle hemoglobinopathies, and understanding of priapism. It does not report a detailed statistical analysis plan, the order in which secondary outcomes were to be tested, or a method for controlling multiplicity. Any adjustment for multiple comparisons is not reported in the registry record.

In general, examining many outcomes or group contrasts can increase the chance that an apparently notable result arises by chance. Whether that concern matters, and how to address it, depends on the planned analyses and whether the goals are descriptive or confirmatory. The registry presents descriptive aims, but does not provide enough analysis detail to determine how multiple outcomes or comparisons were handled.

The analysis population is described as all participants who completed the survey. The record does not report how many people did not complete it, whether partial surveys were included, how missing answers to the primary question were treated, or whether any imputation was used. It also does not report how missing age or diagnosis information was handled. These details matter because the analyzed survey completers may differ from people whose responses are unavailable.

The record does not report whether analyses were conducted according to a prespecified protocol or whether the analysis population changed from an intended population. A formal protocol, statistical analysis plan, and detailed missing-data account are not reported in the registry record. Consequently, the effects of missing responses and the extent of prespecification cannot be assessed.

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 0% reporting threshold.

The registry’s adverse-event entries report serious adverse events and other adverse events separately for each listed group. The reported affected counts are 0 for both categories in each group. The numbers listed at risk are 208 for ages 5-9.9 with HbSS/HbSβ0, 240 for ages 10-14.9 with HbSS/HbSβ0, 398 for ages 15-24.9 with HbSS/HbSβ0, 362 for ages >25 with HbSS/HbSβ0, and 251 for ages >15 with HbSC/HbSβ+.

These entries should be read as registry-reported counts, not as proof that no adverse events occurred. The registry does not report definitions, collection procedures, or a detailed safety-monitoring method for these entries. Death counts are not reported in the registry record. The adverse-event data are distinct from the primary survey question about lifetime history of priapism and do not provide its prevalence result.

Because the study is described as an interview-based epidemiologic study rather than a treatment comparison, these figures do not establish comparative safety between treatments. No treatment groups are described. The zero counts should therefore be interpreted narrowly as the adverse-event counts recorded for the listed groups, with the limitations of the registry reporting.

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

The registry record establishes that the study sought to enumerate males with sickle cell anemia and sickle beta zero thalassemia who answered yes to a question about ever having had priapism. It also specifies that the intended descriptive reporting was by diagnosis and age group, at interview. These features make the research question clear.

What the posted record does not establish is the numerical answer. Primary outcome counts and prevalence estimates are not reported in the registry record. Without them, the amount of reported lifetime history cannot be quantified, and no comparison across age or diagnosis groups can be described. The absence of those results is not evidence that the outcome was absent.

Even if descriptive estimates were available, this design would not show that age or diagnosis caused differences, because the groups were not randomized and may differ in other ways. The study also does not test whether a treatment prevents or changes priapism. Although secondary aims included descriptions of treatment modalities and treatment outcomes, the registry does not report detailed results that would support treatment-effect conclusions.

In general, a survey response about ever experiencing an event is affected by recall and by how participants understand the question. It does not, on its own, reveal when an event occurred, how often it recurred, or how long it lasted. Those issues are relevant to interpreting a lifetime-history measure, but the registry record does not report methods that would resolve them.

The record is therefore informative about the planned descriptive question and its population, but not about the magnitude or precision of its main finding. It does not support clinical recommendations or claims that any intervention works or does not work.

14. Why This Trial Matters Statistically

This study is statistically important as an example of a question that calls for descriptive epidemiology rather than a treatment-effect comparison. The primary endpoint asks how many survey respondents reported ever having experienced priapism. Keeping that question distinct from incidence, episode frequency, or treatment response is essential to interpreting what the measure can represent.

The age and diagnosis groupings also show why denominators and group definitions matter. A count has little meaning without knowing the population assessed, and groups that differ in age and hemoglobin diagnosis are not interchangeable comparison arms. Descriptive stratification can organize information, but it does not by itself explain why outcome frequency might vary.

The record also illustrates the difference between an endpoint definition and a reportable result. It clearly states the survey question and the intended analysis population, yet the primary counts and estimates are not reported. Without those results and measures of uncertainty, readers cannot judge either magnitude or precision. The record’s detail about design does not replace the missing numeric outcome.

Finally, registry entries about adverse events and sample-size illustrations answer different questions from the primary prevalence endpoint. Safety counts do not stand in for lifetime survey responses, and planning calculations do not establish observed power or the precision of a descriptive estimate. Reading each statistic according to its purpose helps prevent overinterpretation. The available record supports a careful account of the question and design, while leaving the core prevalence result unresolved.

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 primary limitation for interpreting this study is that the registry record does not report the primary outcome counts or prevalence estimates. Without the numerator and the relevant group denominators for the survey outcome, the result’s magnitude cannot be assessed. Confidence intervals and other measures of uncertainty are also not reported.

The primary endpoint relies on a participant’s response to a question about ever having had priapism. The registry does not report the survey’s validation, the interview procedures, or how responses were clarified. Recall and differences in understanding may affect lifetime-history responses in general. The record also does not describe how incomplete or missing answers to the primary question were handled.

The analysis population is described as survey completers, but the number and characteristics of people who did not complete the survey are not reported. Recruitment methods, study locations, and additional eligibility criteria are also not reported in the registry record. Without these details, representativeness and possible selection effects cannot be assessed.

The listed groups differ by age and diagnosis and are not randomized comparison groups. Any apparent group contrast, if results were available, could not be attributed to age or diagnosis from the design alone. Adjustment methods and a detailed analysis plan are not reported. The record also does not give enough information to assess multiplicity across the primary and secondary objectives.

Finally, the registry’s adverse-event entries have no reported definitions or detailed collection methods, and death counts are not reported. These safety entries do not resolve the missing primary prevalence findings. The registry records a completed study, but completion status does not supply the absent outcome estimates.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Priapism in Boys and Men With Sickle Cell Disease - Demographics, Characteristics and Prevalence — NCT00300235.
• Registry record last updated 2019-02-01; status last verified 2019-01.
• Results first posted 2009-08-03.
• 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

NCT00300235 is a completed study sponsored by the University of Texas Southwestern Medical Center. The registry records a study start of 2005-08, primary completion of 2008-03, and enrollment of 1464. The study concerned priapism among people with sickle cell disease and collected demographic and clinical information by interview.

The primary outcome was a count of males with sickle cell anemia and sickle beta zero thalassemia who answered yes to a question asking whether they had ever had priapism. The intended reporting was by age and diagnosis, among participants who completed the survey. The registry describes additional groups with HbSC or HbSβ+ diagnoses and secondary aims involving episode characteristics, descriptive comparisons, and understanding of priapism.

The primary counts and prevalence estimates are not reported in the registry record. The record also does not report confidence intervals or detailed methods for missing responses, multiplicity, or the statistical analysis plan. Adverse-event entries report zero affected counts in each listed group; death counts are not reported.