Screening and Brief Advice to Reduce Teen Substance Use: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Screening and Brief Advice to Reduce Teen Substance Use (NCT00227877), a non-randomized na study. The primary outcome is Past-90-day Substance Use at 3 Months Among Baseline Substance Users - New England, USA.

2. Clinical Question

The study also states hypotheses about reducing substance use among patients who screened positive, preventing initiation among those who screened negative, and reducing riding or driving risk among adolescents at risk. Those are broader questions than the registered primary endpoint, which is restricted to baseline users in New England and measures reported use at 3 months. Secondary outcomes listed in the registry concern risky riding or driving at 3 months and 12 months in New England and Prague.

3. Trial Design

This is a completed, parallel-group study with non-randomized allocation and no masking. The registry lists an enrollment of 2695, a start date of 2005-12, and a primary completion date of 2008-12. Boston Children's Hospital is listed as the sponsor. The study phase is listed as NA.

The study was intended to assess brief intervention for adolescent alcohol and drug use in primary care. Its description places the work in primary care offices in New England and pediatric offices in Prague, Czech Republic. The registry lists computer screening and brief physician advice and care as usual in both locations. The intervention description says participants complete a computer-based CRAFFT screen and receive information about health effects, while providers receive screening results and suggested talking points. The registry's intervention description is incomplete at the point where it describes what providers will do with those talking points, so further details are not reported in the registry record.

Non-randomized allocation matters to interpretation: the intervention and control groups may differ for reasons other than the intervention. The record does not report how participants or practices were assigned, whether allocation was determined by location, or what methods were used to address baseline differences. It also does not report whether analyses accounted for participants being treated within offices. The registry itself cautions that the arms are not a like-for-like control comparison. Results from New England and Prague therefore should not be read as if they came from a randomized comparison.

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.

Pre-visit Assessment

Reasons for not completing this period:

Post-visit Checklist

Reasons for not completing this period:

3-months Follow-up

Reasons for not completing this period:

12-months Follow-up

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: 12-18 year old primary care patients who report past-12-month drug or alcohol use at baseline in New England, USA

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 Past-90-day Substance Use at 3 Months Among Baseline Substance Users - New England, USA, measured over Past-90-days at 3 months post-baseline.

The primary endpoint is the number of baseline substance users who reported drug or alcohol use in the past 90 days at the 3-month post-baseline assessment. It applies to 12-18 year old primary care patients in New England who reported drug or alcohol use in the past 12 months at baseline. The unit is participants, and the measure is a count of participants meeting the outcome definition.

This endpoint focuses on subsequent reported use among adolescents already identified as having used substances in the past 12 months. A count can communicate how many participants met the outcome definition, but by itself it does not show the proportion of each group with that outcome or the size and precision of a difference between groups. Such interpretations require the corresponding group denominators and comparative estimates. The primary outcome count and those estimates are not reported in the registry record.

The endpoint relies on self-reported substance use, as described in the study summary. Self-report is the stated measurement approach; the registry does not report additional verification methods or details about the assessment instrument for this primary outcome. The endpoint is a behavioral measure at a specified follow-up assessment, not a measure of diagnoses, long-term outcomes, or all substance use over the entire study period. The reason this particular endpoint was selected as primary is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the primary count represent?

The outcome is a count of participants meeting a yes-or-no definition: reporting drug or alcohol use in the past 90 days at the 3-month assessment. Although the result is recorded as a count, the underlying outcome for each participant is binary: the participant either meets the definition or does not. The count is meaningful only alongside the population eligible for analysis and the number with outcome data. Those group-specific counts and denominators are not reported in the registry record.

Counts and proportions answer different questions. A count states how many participants met the outcome definition; a proportion relates that count to a group denominator. A comparison between groups can be expressed in several ways, including a difference in proportions or a ratio of proportions. Each choice has a different interpretation. The registry record does not report which comparative measure, if any, was used for the primary analysis.

What does a confidence interval add?

General statistical explanation: a confidence interval describes the uncertainty around an estimate under the assumptions of the statistical method. A narrow interval indicates greater precision than a wide interval, while an interval spanning values on both sides of no difference may be compatible with more than one interpretation. An interval does not correct for bias from non-random allocation, incomplete outcome data, or measurement limitations. No confidence interval for the primary result is reported in the registry record.

Why does the non-randomized design matter?

Random assignment, when used and properly implemented, can help balance measured and unmeasured participant characteristics between groups on average. This study is listed as non-randomized, so that protection cannot be assumed. If groups differ at baseline or in the care they receive apart from the intervention, an unadjusted comparison may combine those differences with any intervention-associated difference. Adjustment can sometimes address measured differences, but it cannot guarantee removal of confounding, and it depends on the chosen model and information collected. The registry does not report the assignment process, a statistical adjustment plan, or adjusted primary estimates.

The study took place in multiple primary care offices and two geographic settings. Participants within the same office may share aspects of care or local practice. General statistical explanation: when observations are clustered, treating all participants as fully independent can understate uncertainty if outcomes within a practice are correlated. Methods that account for clustering can be appropriate in that setting. Whether the primary analysis accounted for office-level clustering is not reported in the registry record.

What can be said about the statistical plan?

The registry describes a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the target effect is described as a stated fraction of the observed effect. These are planning assumptions, not results of the trial and not evidence of observed power. The resulting sample-size estimates and the specific effect used are not reported in the registry record. The trial's own sample-size justification is not reported in the registry record.

The primary statistical model, significance threshold for the outcome analysis, handling of baseline values, covariate selection, and method for calculating uncertainty are not reported in the registry record. These details matter because different methods can produce different estimates or standard errors, particularly in a non-randomized study. The record also does not report whether any interim analyses occurred.

The primary endpoint is a participant count, but the registry's general outcome description identifies binary outcomes as participants with an event. General statistical explanation: for binary outcomes, a statistical analysis may compare event counts relative to group sizes, while accounting for design features and missing observations. The choice of effect measure should be stated and interpreted in context. No such primary comparative estimate is reported in the registry record, so it cannot be reconstructed from the endpoint definition alone.

The record describes 12 outcome measures and 12 analyses. The listed secondary outcomes include risky riding or driving at 3 months and 12 months in New England and Prague. The full analysis methods and the reported results for these outcomes are not reported in the registry record. Statistical significance, if reported for multiple outcomes, would need to be considered in light of the number of comparisons and the analysis plan; that plan is not reported.

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("Control - New England, USA", "Computer Screen & Brief Physician Advice - New Eng")
n      <- c(260, 222)
events <- c(162, 121)
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  Control - New England, USA  260  162  62.3  56.1  68.2  56.3  68.0  56.3  68.0
ARM  Computer Screen & Brief Physician Advice - New Eng  222  121  54.5  47.7  61.2  47.9  60.9  47.9  60.9

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 12 outcome measures and 12 analyses, including the primary substance-use outcome and secondary risky riding or driving outcomes at 3 months and 12 months in New England and Prague. The complete outcome list and the mapping between each measure and analysis are not reported in the registry record. The registry does not report whether the analyses were treated as confirmatory or exploratory, which outcomes were prioritized beyond the designated primary endpoint, or whether any adjustment for multiple comparisons was planned or used.

Multiplicity matters because testing several outcomes can increase the chance of at least one apparently unusual result arising by chance. General statistical explanation: interpretation can depend on whether outcomes were prespecified and whether an analysis accounts for multiple testing. Without a reported multiplicity approach and outcome estimates, it is not possible to assess the evidential strength of any secondary finding. No secondary outcome results are reported in the registry record.

Missing-data methods are also not reported in the registry record. The number of participants with missing 3-month outcomes, reasons for missingness, and any imputation or other handling procedures are not reported. The analysis population is not reported, including whether the primary analysis included everyone enrolled, only participants with observed outcomes, or a different defined group. The number eligible for the primary endpoint cannot be inferred from the overall enrollment, since the endpoint is restricted to baseline users in New England and requires a follow-up outcome.

These omissions limit assessment of both bias and precision. If outcome availability differed between groups, a comparison based only on observed outcomes could be misleading. The registry record does not report sensitivity analyses for missing data or analyses of how conclusions might change under alternative assumptions.

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 lists serious adverse events affecting 0 participants and other adverse events affecting 0 participants in each listed group. The groups are Control - New England, with 1068 at risk; Computer Screen & Brief Physician Advice - New England, with 1028 at risk; Control - Czech Republic, with 297 at risk; and Computer Screen & Brief Physician Advice - Czech Republic, with 292 at risk. These figures are safety reporting counts, not the primary substance-use outcome.

The registry lists no serious adverse event terms. Deaths are not reported in the registry record; their status should not be interpreted as a reported zero. The record does not describe the safety collection or ascertainment procedures, the observation period for these counts, or how complete adverse-event reporting was. Therefore, the listed zeros indicate that no affected participants are recorded in these categories, but do not by themselves establish that no events occurred.

These group counts should be read within the study's non-randomized design. The safety figures do not provide a randomized comparison, and they do not establish that the intervention caused or prevented an adverse event. They also do not replace the missing primary efficacy result. No clinical recommendation follows from these registry safety counts.

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

The record defines a study of computer screening and brief physician advice for adolescent substance use and identifies a primary outcome: reported past-90-day drug or alcohol use at the 3-month assessment among baseline users in New England. It also describes hypotheses covering substance use and risky riding or driving. These details clarify what the investigators intended to evaluate.

The record does not report the observed primary outcome count or a comparative estimate. It therefore does not show whether the intervention group had a higher or lower outcome count than the control group, how large any difference was, or how precisely it was estimated. The absence of a result in the registry record should not be interpreted as evidence of no effect.

The design further limits what a group comparison could establish. Allocation was non-randomized, masking was absent, and the registry cautions that the arms are not a like-for-like control comparison. Without information about allocation, baseline differences, and statistical adjustment, an observed group difference would not automatically be attributable to the intervention. The registry also does not report missing-data methods, analysis populations, or adjustment for multiple comparisons.

The primary question concerns a specific population and follow-up: baseline substance users in New England at 3 months. It does not directly answer the separate hypothesis about preventing initiation among those who screened negative, nor does it establish outcomes for Prague or for risky riding and driving. The registry lists those other questions and outcomes, but their results are not reported in the registry record.

Overall, the record supports a description of the trial's purpose, setting, design, and endpoint, alongside limited safety counts. It does not support a conclusion about effectiveness, the size of any difference, or the precision of an intervention effect. Such conclusions would require outcome results and analysis details that are not reported in the registry record.

14. Why This Trial Matters Statistically

This study illustrates why a defined endpoint and a reported result are both necessary for statistical interpretation. The registry specifies who the primary analysis concerns, what behavior is counted, and when it is assessed. Yet without group outcome counts, denominators, and comparative estimates, the endpoint definition alone cannot answer whether the groups differed or how uncertain that comparison would be.

It also highlights the importance of design. A non-randomized study can be informative, but group differences may reflect factors other than the intervention. A reader needs to know how allocation occurred, what baseline differences were present, and how the analysis handled those differences. Those details are not reported in the registry record, which explicitly warns against treating the arms as a like-for-like control comparison.

The study's several outcomes raise further interpretive questions. Multiple endpoints and follow-up times can offer a broader view of the research questions, but the analysis plan and any approach to multiplicity are important for judging findings across them. The record lists 12 outcome measures and 12 analyses, but does not report the full statistical plan or outcome results.

Finally, safety counts and efficacy outcomes serve different purposes. The registry lists zero affected participants for the adverse-event categories in each group, while the primary substance-use result is not reported. Keeping those kinds of information distinct prevents safety reporting from being mistaken for evidence about the primary endpoint. This record is a useful example of how design, endpoint definition, results reporting, and uncertainty all contribute to a sound statistical reading.

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 central limitation for interpretation is that the primary outcome result is not reported in the registry record. Group-specific counts, denominators, effect estimates, confidence intervals, and p-values are not reported. As a result, the magnitude, direction, and precision of the primary comparison cannot be assessed.

The design is non-randomized and unmasked. The registry explicitly cautions that the arms are not a like-for-like control comparison. The allocation process, baseline comparability, and any adjustment for confounding are not reported in the registry record. The record also does not report whether analyses accounted for possible clustering of patients within primary care offices.

The endpoint is based on self-reported substance use. The record does not report additional verification procedures or details about the primary outcome assessment instrument. Missing outcome data, reasons for missingness, handling of missing data, and the analysis population are not reported. These gaps prevent assessment of whether follow-up or outcome availability could affect the comparison.

The primary endpoint is specific to baseline users in New England at 3 months. The broader hypotheses include other populations and behaviors, but results for the listed secondary outcomes are not reported in the registry record. The complete analysis plan, multiplicity approach, and protocol-based sample-size justification are also not reported. Together, these limitations mean that the record describes the research question and design more fully than it documents the statistical findings.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Screening and Brief Advice to Reduce Teen Substance Use — NCT00227877.
• Registry record last updated 2019-08-14; status last verified 2019-08.
• Results first posted 2018-09-21.
• 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

The registry describes a completed, parallel, non-randomized study of computer screening and brief physician advice for adolescent substance use, with care as usual as the comparator. The study was sponsored by Boston Children's Hospital and lists enrollment of 2695, a start date of 2005-12, and a primary completion date of 2008-12.

The primary endpoint is the count of New England patients aged 12-18 who reported past-90-day substance use at 3 months, among those reporting past-12-month use at baseline. The registry does not report the primary outcome result, comparative estimates, uncertainty measures, or key analysis details. It lists zero participants affected by serious and other adverse events in each group; deaths are not reported in the registry record. The non-randomized design and the registry's caution that the arms are not like-for-like comparisons are central to interpreting the study.