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 Contingency Management Treatment for Crack Addiction - Study With Brazilian Population (NCT01815645), a randomized na study. The primary outcome is Longest Duaration of Achieved Abstinance.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01815645 |
| Phase | NA |
| Condition | Cocaine Related Disorders |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 65 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Federal University of São Paulo |
| Results posted | Yes |
2. Clinical Question
Population
People receiving ambulatory treatment for crack addiction in Brazil. The registry lists cocaine-related disorders as the condition and an enrollment of 65.
Intervention
Standard ambulatory treatment plus contingency management (ST+CM), delivered over 12 weeks. The description says participants received the treatment provided by the ambulatory service where the study was conducted, with contingency management added.
Comparator
Standard ambulatory treatment alone over 12 weeks, described as the treatment provided by the same ambulatory service where the study was conducted.
Primary question
How did the groups compare in the longest duration of continued abstinence, defined by consecutive negative crack/cocaine samples submitted during treatment? The registry describes participant counts at 4, 8 and 12 weeks, but the results are not reported in the registry record.
The clinical question is whether adding contingency management to the local standard ambulatory treatment was associated with different abstinence-duration outcomes during the treatment period. The registry identifies a randomized, parallel-group comparison. It does not report the randomization procedure, how treatment was assigned in practice, or whether any participants crossed between treatments.
The endpoint concerns consecutive negative samples rather than simply whether a participant ever submitted a negative sample. That distinction makes the outcome a measure of sustained abstinence as reflected in submitted samples. It does not, by itself, establish what happened between samples or outside the observation period. Details such as the sample collection schedule, the method used to test samples, and how missed or unusable samples were handled are not reported in the registry record.
The record identifies secondary outcomes concerning the percentage of submitted samples negative for alcohol use and for marihuana use. It does not report their results. It also does not provide enough information to determine whether the reported treatment comparison accounted for other participant characteristics or used an adjusted statistical model.
3. Trial Design
This was a randomized controlled trial with a parallel-group design and no masking listed. The registry identifies two behavioral interventions: standard treatment and standard treatment plus contingency management. It lists an enrollment of 65. The record does not report the method used to generate the random sequence, the process used to conceal assignments before enrollment, or the allocation ratio in the trial itself. Equal allocation appears only among the assumptions for planning illustrations, not as a reported feature of the trial’s allocation.
Both group descriptions specify 12 weeks of treatment. Standard treatment alone consisted of the treatment provided by the ambulatory service conducting the study. The ST+CM group was to receive that same service treatment plus contingency management. The registry does not give further details about the standard treatment content, the contingency-management procedures, treatment attendance, or adherence to either intervention.
The study is listed as completed. Its recorded start is 2012-05 and its primary completion is 2015-06. The sponsor is the Federal University of São Paulo. The phase is listed as NA, which is the registry designation; the record does not provide further phase information.
The primary outcome is described as the number of participants reaching 4, 8 and 12 weeks of continued abstinence, based on the highest amount of consecutive negative crack/cocaine samples submitted. These are multiple duration categories, rather than one clearly specified binary contrast in the registry record. The record does not report group-level outcome counts, an effect estimate, a confidence interval, or a test of the primary outcome. It also does not describe an analysis population, such as all randomized participants or only participants who completed treatment.
Six outcome measures are listed in total, with two secondary outcomes named: the percentage of samples submitted that were negative for alcohol use and for marihuana use. The remaining outcome descriptions and results are not reported in the registry record. No statistical analyses are listed.
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 | Standard Treatment | Standard Treatment Plus Contingency Management |
|---|---|---|
| STARTED | 32 | 33 |
| COMPLETED | 32 | 33 |
| NOT COMPLETED | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: Longest duaration of abstinance was determined by the highest amount of consecutive negative crack/cocaine samples submitted.
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 | Standard Treatment | Standard Treatment Plus Contingency Management | Total |
|---|---|---|---|---|
| Participants analysed | 32 | 33 | 65 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 32 | 33 | 65 |
| Age, Categorical: >=65 years | Participants | 0 | 0 | 0 |
| Age, Continuous | years | 35.4 (SD 8.5) | 35.3 (SD 8.7) | 35.3 (SD 8.6) |
| Sex: Female, Male: Female | Participants | 6 | 3 | 9 |
| Sex: Female, Male: Male | Participants | 26 | 30 | 56 |
| Region of Enrollment: Brazil | participants | 32 | 33 | 65 |
6. Primary Endpoint
The registry lists the primary outcome as Longest Duaration of Achieved Abstinance, measured over 12 weeks of treatment.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | number of participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the longest duration of continued abstinence during 12 weeks of treatment, represented by the number of participants achieving 4, 8 or 12 weeks. The registry says duration was determined by the highest amount of consecutive negative crack/cocaine samples submitted. In practical terms, the endpoint uses a sequence of submitted samples to classify how long a period of consecutive negative results was observed.
This type of endpoint is used to represent continuity of abstinence, rather than an isolated negative result. Requiring consecutive negative samples focuses the measure on a sustained pattern during the observation period. It also makes the result dependent on the sampling process: the timing and completeness of sample submission, the rules for interpreting missing samples, and the test procedures all affect what can be concluded. Those operational details are not reported in the registry record.
The listed categories of 4, 8 and 12 weeks describe different durations, not three independent measurements of the same kind. A participant reaching a longer duration may also meet a shorter-duration threshold, depending on the endpoint rules. The record does not specify the exact statistical comparison among these categories, and its primary outcome is not reduced to a single comparison in the registry record.
No observed counts by group, treatment effect, or uncertainty estimate for this endpoint are reported in the registry record. As a result, the endpoint definition can be explained, but the relative abstinence outcomes of the two groups cannot be interpreted from the registry information available.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record supports a description of the trial question and design, but it does not report the primary outcome results. It names participant counts at 4, 8 and 12 weeks of continued abstinence as the primary outcome, yet provides no group-specific counts or comparison. There is therefore no reported estimate of how the groups differed on the primary endpoint and no reported measure of the precision of such an estimate.
In particular, the record does not provide a confidence interval or a p-value for the primary outcome. A confidence interval would ordinarily describe the range of effect sizes reasonably compatible with the observed data under a specified statistical model. Without an effect estimate and its uncertainty, neither the direction nor the magnitude of the primary comparison can be assessed from this record. No conclusion about the comparative outcome should be inferred from the study title, rationale, intervention descriptions, or completion status.
The endpoint is based on consecutive negative crack/cocaine samples, so its interpretation depends on how samples were collected and how missing submissions were classified. The registry does not report those details. Even if group-level counts were available, they would describe the outcome as operationalized through submitted samples; they would not automatically describe all behavior between samples or beyond the 12-week treatment period.
The record names two secondary outcomes: the percentage of submitted samples negative for alcohol use and the percentage negative for marihuana use. Their results are not reported. It also does not name the other outcome measures among the six listed measures. No analysis results are listed, so no secondary outcome or alternative analysis can fill the gap in the primary result.
The safety information is descriptive. For standard treatment, the record lists 32 participants at risk for serious adverse events, zero serious adverse events, 32 at risk for other adverse events, zero other adverse events, and zero deaths. For standard treatment plus contingency management, it lists 33 at risk for serious adverse events, zero serious adverse events, 33 at risk for other adverse events, and zero other adverse events, with zero deaths. These are the recorded counts; the registry does not provide further details about event definitions, collection procedures, or follow-up duration for safety reporting.
The appropriate reading is therefore limited: a randomized, parallel-group study was registered and completed, with a 12-week abstinence endpoint and safety counts recorded. The comparative primary results and the statistical analysis needed to evaluate them are not reported in the registry record. This is an absence of reported results, not evidence that the groups had the same outcome or that a difference was present.
9. Statistical Methods Explained
The registry describes a randomized, parallel-group trial without masking. Randomization is a design method intended to make treatment assignment independent of participants’ measured and unmeasured characteristics, on average. This can support a fair comparison, although random assignment alone does not guarantee that groups will be balanced in a particular study. The registry does not report how the random sequence was generated, how assignment was concealed, or how the comparison was analyzed.
What does the endpoint count?
The primary outcome is a count of participants reaching specified durations of continued abstinence: 4, 8 and 12 weeks. The registry defines the duration using the highest amount of consecutive negative crack/cocaine samples submitted. An outcome expressed as a participant count is a categorical outcome: each participant is classified according to whether a duration threshold was reached, according to the study’s rules. The registry does not report the observed counts in either group, so no comparison of those categories can be reconstructed from the record.
When an outcome has several categories or thresholds, an analysis must specify how they will be compared. Possible approaches in general include comparing one prespecified threshold, comparing the full distribution across ordered categories, or using a model that accounts for the ordering. These approaches answer different questions and may require different assumptions. The registry does not report which approach was used for this endpoint. Its description of multiple duration categories is not a substitute for an analysis plan or an observed result.
Why does missingness matter?
The endpoint relies on samples that were submitted. A missing sample is not automatically equivalent to a negative or positive sample; the handling rule must be defined. If missing submissions differ across groups or are related to the likelihood of abstinence, the estimated comparison can be affected. General methods include analyzing according to a prespecified missing-data rule, using a model that makes explicit assumptions about missing observations, or examining how conclusions change under alternative assumptions. The registry does not report the sampling schedule, the frequency of missing samples, the handling of missing results, or any sensitivity analysis.
There is also a distinction between a missing sample and a submitted sample with a test result. The endpoint description refers to consecutive negative samples, but does not say how a sequence was interrupted or classified when a sample was not submitted. Without this operational information, readers cannot fully assess how the endpoint represents sustained abstinence.
What can an uncertainty estimate show?
In general, an effect estimate describes the observed contrast between groups, while a confidence interval communicates uncertainty around that estimate under the chosen model. A narrow interval indicates greater statistical precision than a wide interval, but neither width nor location can be judged without the reported estimate and interval. A p-value, when reported, addresses compatibility of the data with a specified null hypothesis under a statistical model; it does not measure the size or clinical importance of an effect. The registry record reports no primary effect estimate, confidence interval, or p-value.
For outcomes represented by participant counts, statistical analysis may compare proportions or model the category structure. The appropriate method depends on the endpoint definition, the prespecified contrast, and relevant assumptions. The record classifies the primary outcome as binary in its general outcome information, but the endpoint description contains several duration categories. It does not specify the coding or model that resolves this structure. No method should be attributed to the investigators beyond what is reported.
How should planning illustrations be read?
General sample-size calculations ask how many participants would be needed under assumed design conditions to detect a specified effect with a chosen probability of statistical detection. The registry’s planning assumptions describe a two-sided significance level of 0.05, equal allocation between arms, a normal approximation, and effects expressed as fractions of the observed effect. These are assumptions for planning illustrations, not a report of the trial’s actual allocation procedure or its original design justification.
A sample-size illustration based on an observed effect is conditional on that effect estimate. It does not indicate the probability that the completed trial detected an effect and must not be read as observed power. The registry record does not report the effect estimates or the numerical planning results needed to interpret a particular illustration. Sample-size calculations are also sensitive to assumptions about variability, allocation, outcome definition, and analysis method. The registry does not report the original sample-size justification or whether it used different assumptions.
For time-to-event outcomes, some planning methods express the required quantity as a total number of events; for other outcomes, planning quantities may be stated as participants per arm. The assumptions in the record distinguish these conventions. They do not change the fact that the primary endpoint is a set of abstinence-duration categories, and the registry provides no primary analysis result.
No statistical analyses are listed in the registry record. It does not report a statistical model, covariate adjustment, interim analysis, or a prespecified analysis population. These omissions prevent a detailed assessment of the analysis strategy and make it important to separate the registered endpoint description from any claim about what the trial found.
10. Multiplicity, Missing Data and Analysis Populations
The primary outcome is described at 4, 8 and 12 weeks of continued abstinence. Testing or interpreting several durations can raise a multiplicity question: if multiple comparisons are made, the chance of finding an apparently notable result by chance may differ from that for one prespecified comparison. General approaches include defining one primary contrast in advance, adjusting for multiple tests, or treating results across thresholds as a coordinated set. The registry record does not report which comparison was prespecified or whether any multiplicity procedure was planned or used.
There are six outcome measures listed, and the record names two secondary outcomes concerning negative samples for alcohol use and marihuana use. Results for those outcomes are not reported. The registry does not explain how the primary and secondary outcomes were prioritized or how interpretation across outcomes was handled. The existence of multiple outcomes alone does not establish that a particular adjustment was required or performed.
The record does not report the number or pattern of missing outcome samples, reasons for non-submission, or methods for handling missing data. It also does not describe withdrawals, exclusions after randomization, or a sensitivity analysis for missing observations. These details are relevant because the primary endpoint is based on submitted samples and consecutive negative results.
No analysis population is reported. For example, the registry does not say whether the primary comparison included everyone randomized, only participants who started treatment, or a different defined group. It also does not report whether participants were analyzed according to their randomized assignments. Such information is needed to understand the population represented by an effect estimate; no effect estimate is available in this record.
The registry lists no statistical analyses. It does not report an analysis plan, interim analyses, or whether analysis decisions were made before outcome data were reviewed. These items are not reported in the registry record, so no assumptions should be made about how multiplicity, missing data, or analysis populations were handled.
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 |
|---|---|---|---|
| Standard Treatment | 0 | 32 | 0.0% |
| Standard Treatment Plus Contingency Management | 0 | 33 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Standard Treatment | 0 of 32 |
| Standard Treatment Plus Contingency Management | 0 of 33 |
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 |
|---|---|
| Standard Treatment | 0 of 32 |
| Standard Treatment Plus Contingency Management | 0 of 33 |
The registry reports serious adverse event counts, other adverse event counts, and deaths for both groups. For standard treatment, 32 participants are listed as at risk for serious adverse events and 32 as at risk for other adverse events; the corresponding event counts are zero and zero, and deaths are zero. For standard treatment plus contingency management, 33 are listed as at risk for serious adverse events and 33 as at risk for other adverse events; the event counts are zero and zero, and deaths are zero.
These figures describe what was recorded in the registry. They do not provide event-level descriptions, severity details beyond the serious-versus-other classification, or the length and completeness of safety follow-up. The record also does not describe how adverse events were solicited, defined, reviewed, or attributed to treatment. Consequently, the counts should not be taken as a complete account of all possible harms or as a comparison adjusted for differences in observation time.
A zero count means that no event of the listed type is recorded for that group in this registry entry. It does not establish that the underlying risk is zero. With no additional safety detail or comparative analysis reported, the entries are best read as descriptive counts rather than evidence of equivalence between treatments.
12. What the Result Does, and Does Not, Mean
The registry record establishes that a randomized, parallel-group study compared standard ambulatory treatment with the same treatment plus contingency management for people receiving care for crack addiction. It defines a primary outcome based on the longest duration of consecutive negative crack/cocaine samples submitted during 12 weeks of treatment. It also records safety counts for serious adverse events, other adverse events, and deaths.
It does not report the observed primary outcome counts or a statistical comparison between groups. Therefore, the record cannot show whether one group had longer observed abstinence, how large any difference was, or how precise an estimate might be. It also cannot establish that the groups were equivalent. A missing result is not a null result: the absence of a reported comparison leaves the comparative question unanswered in this registry record.
The endpoint has a specific scope. It concerns the sequence of submitted samples during the treatment period, rather than every moment of behavior or outcomes after treatment. The registry does not report sample collection details or the handling of missing samples, which limits interpretation of how closely the measure reflects the underlying pattern of use.
The recorded zero adverse-event counts are descriptive and do not prove that no risk exists. The entry does not give detailed event definitions or safety follow-up information. Likewise, the listing of secondary outcomes does not show that those outcomes were analyzed or that their results support a particular conclusion.
In general, a trial result is best understood through its treatment contrast, uncertainty interval, analysis population, and outcome-handling rules. Those elements are not reported for the primary comparison. The registry record can support a description of the trial’s design and registered endpoint, but not a conclusion about the comparative efficacy or overall safety of the two treatment approaches.
13. Why This Trial Matters Statistically
This study addresses a statistical challenge common in behavioral treatment research: defining an outcome that represents sustained change rather than a single observation. The registry’s endpoint uses consecutive negative crack/cocaine samples to define the longest abstinence duration. This makes the measurement rule central to interpretation. Sample submission, sequence rules, and missing observations can influence how a participant is classified, so transparent reporting of those details is important.
The trial also illustrates why a clear primary contrast matters when an outcome includes several thresholds. Counts at 4, 8 and 12 weeks describe different durations, and the way those categories are analyzed affects the question answered. A prespecified comparison and a reported estimate with uncertainty would help readers distinguish a potentially important difference from imprecise evidence. The registry does not report those analysis details or results.
Randomized allocation can provide a strong framework for comparing interventions, but the design alone does not communicate the result. Interpretation also requires information about the allocation process, adherence, participant flow, missing data, analysis population, and statistical methods. These details are not reported in the registry record, limiting assessment of how the study’s design translated into its analysis.
The record’s safety counts also illustrate the difference between descriptive event reporting and a comparative safety analysis. Event counts are useful information, but they do not by themselves describe uncertainty or establish that treatments have equal safety. Overall, the statistical importance of this trial lies in the question and endpoint it registered; the missing comparative results prevent readers from using the record to quantify what the trial found.
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 principal limitation for interpreting this trial from the registry record is that it does not report the primary outcome results. There are no group-specific counts for the 4-, 8- or 12-week abstinence categories, no effect estimate, and no confidence interval or p-value. The comparative outcome cannot therefore be evaluated from the record.
The endpoint definition is only partly operationalized. It relies on consecutive negative samples submitted, but the registry does not report the sampling schedule, testing procedures, rules for missing or unusable samples, or how interruptions in a sequence were classified. These details matter to the interpretation of a duration based on submitted samples.
Several aspects of trial conduct and analysis are also not reported in the registry record. These include the random-sequence method, allocation concealment, participant flow, adherence, treatment fidelity, analysis population, statistical model, and any adjustment for multiple comparisons. The content of standard ambulatory treatment is described only as the service’s exact treatment; further components are not listed. The registry does not report whether observed differences in other participant characteristics were considered in the analysis.
The registry lists six outcome measures but names only two secondary outcomes in the record, and does not report their results. It also lists no analyses. The safety counts are not accompanied by detailed event descriptions or information about ascertainment and follow-up. These limitations mean that the entry is useful for identifying the trial design and endpoint, but insufficient for a full assessment of its statistical results or the completeness of outcome reporting.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Contingency Management Treatment for Crack Addiction - Study With Brazilian Population — NCT01815645.
- Registry record last updated 2017-07-27; status last verified 2017-07.
- Results first posted 2017-06-19.
- 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
NCT01815645 is a completed randomized, parallel-group trial sponsored by the Federal University of São Paulo. The registry lists an enrollment of 65, a start of 2012-05, and a primary completion of 2015-06. The comparison was standard ambulatory treatment alone versus the same treatment plus contingency management, with both group descriptions specifying 12 weeks of treatment.
The primary outcome was the number of participants reaching 4, 8 and 12 weeks of continued abstinence, defined by the longest sequence of consecutive negative crack/cocaine samples submitted. The registry does not report outcome counts, a treatment-effect estimate, or a statistical analysis for this comparison. It lists secondary outcomes concerning samples negative for alcohol use and marihuana use, without results.
The safety entry records zero serious adverse events, zero other adverse events, and zero deaths in each group. The registry does not report further safety details, an analysis population, missing-data methods, or a statistical plan.