Computerized Brief Intervention vs. Delayed Computerized Brief Intervention: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Computerized Brief Intervention vs. Delayed Computerized Brief Intervention (NCT01936623), a randomized na study. The primary outcome is Alcohol, Smoking, and Substance Involvement Screening Tests (ASSIST) Global Continuum of Illicit Drug Risk Score.

2. Clinical Question

3. Trial Design

The study is listed as randomized, with a parallel-group model and no masking. The registry records enrollment of 80 and lists 40 participants in each arm for the primary outcome. The study is marked completed. Its start is recorded as 2013-08 and its primary completion as 2014-09. The phase is listed as NA.

The intervention arm received the computerized brief intervention, described as a talking, animated cartoon-like parrot that offers feedback, empathic reflection and personalization regarding drug use. Participants in the delayed-intervention arm received only a substance abuse assessment at baseline and then received the computerized intervention at three-month follow-up. The study summary describes its purpose as determining whether the computerized intervention was more effective than an assessment alone for adult primary care patients with moderate-risk drug use.

The primary outcome was the ASSIST Global Continuum of Illicit Drug Risk Score at 3 month follow-up. The registry reports least-squares means with standard errors for the arms, as well as a mean difference and an interval estimate. A secondary outcome entry concerns the same score at 6-month follow-up. Four outcome measures are recorded, but the registry lists no reported analyses. It does not report the allocation procedure beyond randomized allocation, the details of sequence generation or concealment, or the analysis population.

The delayed arm's receipt of the intervention at three-month follow-up is relevant when reading follow-up results. The registry does not specify further details about the timing of outcome assessment relative to that intervention or provide a fuller account of the study schedule. Information on site, recruitment methods and participant characteristics is not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Reasons for not completing this period:

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Alcohol, Smoking, and Substance Involvement Screening Tests (ASSIST) Global Continuum of Illicit Drug Risk Score, measured over 3 month follow-up.

The primary endpoint is the ASSIST Global Continuum of Illicit Drug Risk Score, assessed at 3 month follow-up. The registry describes the scale as ranging from 0 to 308; higher scores indicate greater risk. The score is a continuous measure, so the reported arm summaries are means rather than event counts or proportions. The registry gives least-squares means and standard errors for each arm.

A continuous risk score can represent differences in the measured level of risk across participants, rather than reducing the result to a yes-or-no outcome. That can be useful when the study question concerns a change in the overall measured continuum. This is a general explanation of the statistical role of continuous outcomes; it does not establish how clinically important a particular score difference is. A threshold for meaningful change, a minimally important difference or a rationale for choosing this score as the primary endpoint is not reported in the registry record.

The measure is used to assess the study's stated question about a computerized brief intervention for moderate-risk drug use. Its interpretation should remain tied to the scale as described: higher scores represent greater risk. The endpoint is not, by itself, a direct measure of every aspect of drug use, functioning or health. The registry does not report additional validation or measurement details for this trial.

7. Results Posted in the Registry

• Delayed Computerized Brief Intervention: mean 27.80 versus 24.40 on control; difference 3.40 (95% CI -2.70 to 9.50), standardized effect d = 0.24; z-test p = 0.274.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Alcohol, Smoking, and Substance Involvement Screening Tests (ASSIST) Global Continuum of Illicit Drug Risk Score

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • Delayed Computerized Brief Intervention: mean 27.10 versus 26.40 on control; difference 0.70 (95% CI -5.40 to 6.80), standardized effect d = 0.05; z-test p = 0.822.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Delayed Computerized Brief Intervention and the control. The interval gives the range of effects that remain compatible with the data.

The registry posts a secondary result for the same ASSIST Global Continuum of Illicit Drug Risk Score at 6-month follow-up. At a broad level, its estimated contrast points in the same direction as the primary result, but its interval also includes no difference. The later finding therefore does not clearly reinforce a separation between the groups. It is most useful as a related follow-up observation, not as independent confirmation of the primary result, because it concerns the same measure in the same trial.

The registry lists one secondary outcome entry and reports no secondary analyses. It does not provide a multiplicity plan or say whether this follow-up result was prespecified. When several outcomes, time points or comparisons are examined, the chance of at least one apparently unusual result can increase. This is a general statistical concern, not a claim that a particular false-positive result occurred in this study. Adjustment procedures or a clear hierarchy of outcomes can help control how such evidence is interpreted, but their use is not reported in the registry record.

Unadjusted secondary results generally carry less weight than a clearly prespecified primary result because they may be more exploratory and may be affected by multiple testing. They can still help describe whether the pattern is consistent across time, but they should not be treated as independent proof of the primary finding. In this record, the absence of a reported analysis plan, adjustment strategy and details about missing follow-up data limits how strongly the secondary result can add to the interpretation.

The secondary result should also be read in the context of the delayed arm's planned receipt of the computerized intervention at three-month follow-up. The registry does not provide enough detail about outcome timing and intervention exposure to attribute any change over time to a particular mechanism. A comparison at later follow-up cannot, on its own, establish persistence or change in an intervention effect.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Alcohol, Smoking, and Substance Involvement Screening Tests (ASSIST) Global Continuum of Illicit Drug Risk Score

9. Statistical Interpretation

10. Statistical Methods Explained

The primary endpoint is continuous, and the registry reports a least-squares mean for each arm. A mean describes the center of a distribution of measured scores. A least-squares mean is a model-based group mean; however, the registry does not report the model specification or covariates used to obtain these means. The standard error describes the uncertainty in an estimated mean. It is not the same as the standard deviation of individual participant scores: the standard error concerns the estimate, while the standard deviation describes variation among observations.

What does the mean difference represent?

The posted comparison is expressed as a mean difference for delayed computerized brief intervention relative to computerized brief intervention. The estimated difference is 3.4 units. Since the delayed-intervention arm has the higher reported mean, this positive contrast corresponds to a higher score in that arm. Higher scores on the registry's scale indicate greater risk. This is a description of the direction of the estimate, not a claim about clinical importance or a treatment effect beyond the uncertainty in the data.

A difference of zero would indicate equal group means under the contrast as defined. The interval estimate extends from -2.698 to 9.498 and crosses zero, so it includes no difference as well as differences in either direction. An interval gives a set of values compatible with the data and the method used to calculate it. It is not a guarantee that the true value lies within the interval, and it does not show that all values inside are equally plausible.

How should the p-value be understood?

The unadjusted p-value for the primary comparison is 0.274. In general, a p-value measures how unusual results at least as incompatible with a specified null hypothesis would be if that hypothesis and the statistical model were correct. It is not the probability that the null hypothesis is true, nor is it a measure of the size or importance of the observed difference. At the 0.05 significance level used in the planning assumptions, this p-value does not meet that threshold. The registry does not report the trial's own prespecified significance threshold or full analysis plan, so the comparison should not be read as a complete account of all planned inferential procedures.

The p-value and confidence interval tell related but not identical parts of the story. The interval describes uncertainty in the estimated difference on the score scale. The p-value gives a measure of compatibility with a null value under a test. Here both support caution: the point estimate is not precise enough to rule out no difference, and the p-value is not small relative to the 0.05 planning threshold. Neither result establishes equivalence.

Why do standard errors and distributional assumptions matter?

Standard errors are used to quantify uncertainty around estimated means and contrasts. In general, the accuracy of those estimates depends on features such as the sampling process, outcome distribution and analysis model. The registry reports a standard error of 2.2 for each primary arm mean. It does not report diagnostic checks or the model details needed to assess the assumptions behind the least-squares means.

The sample-size illustration uses a normal approximation, as stated in the registry record. This is a planning assumption for the illustration, not a statement that the trial's outcome values followed a normal distribution. For continuous outcomes, departures from model assumptions can affect estimated uncertainty. Over-dispersion, in general, means that observed variability exceeds what a model assumes; if it is not accommodated, uncertainty can be understated. The registry does not report an over-dispersion assessment, and the result should not be described as having such a problem.

The comparison also includes a pooled standard deviation described as approximate. A standard deviation summarizes variability among individual scores, unlike the standard error of a group mean. The approximate pooled value is used for the planning illustration of effects, rather than replacing the registry's primary reported mean difference. Because it is approximate, the planning display should be read as an illustration rather than as a fully specified design calculation.

What does randomization contribute?

Random assignment is intended, in general, to make treatment groups comparable on average with respect to measured and unmeasured characteristics. It does not guarantee balance in a particular trial, especially when groups are limited in size. The record identifies randomized allocation but does not describe how the random sequence was generated, concealed or implemented. It also lists no masking. These details matter because predictable allocation or knowledge of assigned group can introduce bias in some parts of a study, particularly when outcomes involve participant responses. The registry does not provide enough information to determine whether such bias occurred.

The record lists no reported analyses, despite posting outcome summaries and comparisons. The model behind the least-squares means, any covariate adjustment, the handling of missing values and the analysis population are not reported in the registry record. General statistical explanations can clarify the meaning of the displayed estimates, but they cannot fill in those trial-specific methodological details.

11. Confidence Intervals and Precision

The primary mean difference is 3.4 units, with a confidence interval from -2.698 to 9.498. The interval crosses zero. It therefore does not rule out no difference, and it also contains values on both sides of zero. With the contrast expressed as delayed intervention minus computerized intervention, the positive point estimate indicates a higher score in the delayed-intervention group, but the interval leaves considerable uncertainty about the size and direction of the underlying difference.

Confidence intervals are generally used to communicate both an estimate and its statistical precision. A narrower interval indicates greater precision for the quantity being estimated, while a wider interval leaves more possible values compatible with the data and method. The primary interval is broad relative to its point estimate, so the result does not pinpoint a narrow range of group differences. The score's range is 0 to 308, but the registry does not give a threshold for interpreting a difference as clinically important.

The arm standard errors are 2.2 in each group. These quantify uncertainty in the estimated group means, not the spread of individual scores. The posted comparison interval and the unadjusted p-value of 0.274 are consistent with substantial uncertainty about whether the groups differed. Statistical nonsignificance does not establish equivalence, and a confidence interval is not a probability statement about the true effect. The registry does not report a prespecified equivalence margin or non-inferiority framework.

Precision also depends on the population and analysis actually represented. The registry lists 40 participants per arm for the primary outcome, but does not explain whether all randomized participants contributed to the outcome summaries or how missing measurements were handled. Without that information, the interval can be interpreted as reported, while the impact of missingness on precision cannot be assessed from the registry record.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. The table and curve are planning illustrations based on the observed effect and are not the trial's original sample-size justification. The registry's own design assumptions for its sample-size calculation are not reported in the registry record.

The illustration assumes a two-sided significance level of 0.05, equal allocation between the two arms and a normal approximation. It considers detecting the stated fraction of the observed effect. The rows therefore describe planning for 100%, 75% or 50% of the observed effect, rather than separate effects observed in new participants. For each assumed effect, the 80% power column gives the participants per arm estimated to provide an 80% chance of detecting that effect under the stated assumptions if it is present. The 90% power column gives the corresponding planning target for a 90% chance under those assumptions.

Smaller effects require more participants to detect because they are harder to distinguish from random variation. Thus, the planning targets rise as the assumed fraction of the observed effect gets smaller. The values depend on the effect chosen and the stated assumptions; they should not be read as guaranteed enrollment requirements for a future study. This is not observed power.

The trial enrolled 80, with 40 participants listed in each arm for the primary outcome. That enrollment is distinct from the planning illustrations, which are calculated from the observed comparison and specified assumptions. The registry does not report the original rationale for the trial's enrollment target, any allowance for missing follow-up measurements, or whether the original design used an effect different from the one observed.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 3.400; pooled standard deviation σ = 13.914.
2. n = 2 × (1.96 + 0.842)² × 13.914² / 3.400² = 262.9, rounded up to 263 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 3.4                      # observed difference in means
sigma <- 13.9140217047409                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1936623)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 263 (80% power), 352 (90% power)
 75% of observed effect: n per arm = 468 (80% power), 626 (90% power)
 50% of observed effect: n per arm = 1,052 (80% power), 1,408 (90% power)
power.t.test: 263.9 
Simulated power at n = 263 per arm: 0.799 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry identifies a primary endpoint and records four outcome measures, while one secondary outcome entry is posted. It lists no reported analyses. It does not report a statistical analysis plan, the hierarchy among outcomes and time points, or whether any multiplicity adjustment was prespecified or applied. These details matter because interpreting multiple tests as though each were the only test can increase the chance of a false-positive finding. This is a general issue in statistical inference; the available record does not establish that such an error occurred.

The primary comparison is reported with an unadjusted p-value. No adjusted p-value or multiplicity procedure is reported in the registry record. The posted primary result can be described on its own terms, but the broader strength of evidence across the outcome set cannot be judged without knowing which comparisons were planned and how the study intended to handle them. The lack of reported analyses also leaves unclear whether the posted results represent all analyses conducted.

Missing-data information is not reported. The registry does not state how many participants completed the 3 month or 6-month assessments, whether outcomes were missing, why they may have been missing, or how missing observations were handled. It also does not describe any imputation, sensitivity analysis or complete-case restriction. Missing data can affect both the precision and the validity of a comparison, depending on their amount and pattern. Without trial-specific information, their impact cannot be determined.

The analysis population is not reported in the registry record. In particular, the record does not say whether the estimates were based on all randomized participants, participants with observed outcome data, or another defined group. Random assignment supports comparisons based on assigned groups when the analysis preserves that assignment appropriately, but the record does not provide enough detail to verify the analysis approach. The displayed group counts describe the posted outcome summaries and should not be taken as a complete account of participant flow.

15. 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 records zero serious adverse events among 40 participants at risk in the computerized brief intervention group and zero among 40 participants at risk in the delayed-intervention group. It also records zero other adverse events among 40 participants at risk in each group. No serious adverse event terms are listed. These are the reported counts for the registry's adverse-event categories.

Zero recorded events in these groups does not establish that no adverse events occurred outside the registry's reporting definitions or observation period. The record does not provide further information about how events were collected, how long participants were monitored for adverse events, or what criteria were used for classification. Death counts are not reported in the registry record.

Adverse-event counts are descriptive and should be read separately from the primary outcome comparison. The registry's zero counts do not establish a general safety profile, and the record does not provide enough detail to compare risks beyond the reported categories and groups. The figures describe what is entered in the registry, not an independent assessment of all possible safety outcomes.

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

The result describes a randomized comparison of a computerized brief intervention with delayed access to that intervention among adult primary care patients with moderate-risk drug use. At 3 month follow-up, the posted score means differ by 3.4 units in the direction of a higher score in the delayed-intervention group. The interval includes zero and the unadjusted p-value is 0.274, so the registry result does not provide strong statistical evidence of a group difference under the 0.05 planning threshold.

That interpretation is not the same as saying the intervention has no effect. The estimate is uncertain, and the interval allows differences in either direction. Nor does the result show that the groups are equivalent: the registry reports no equivalence margin or analysis. A nonsignificant comparison can arise when an effect is absent, when an effect is modest, or when an estimate is too imprecise to distinguish possible effects from no difference. The posted result alone cannot resolve those possibilities.

The endpoint is a risk score ranging from 0 to 308, with higher scores indicating greater risk. The registry does not report a clinically important difference threshold, so the clinical meaning of a difference of this size cannot be determined from the record. Statistical evidence and clinical importance are different questions: an estimate can be statistically distinguishable yet not clinically important, or potentially important but too imprecise to establish.

The finding applies most directly to the trial comparison and the outcome as registered. Details on participant characteristics, care outside the study, analysis populations and missing data are not reported. The record also lists no masking and does not provide the statistical analysis plan. Those limitations make it inappropriate to extend the result to other populations, settings, intervention versions or follow-up periods without additional evidence. This interpretation describes the posted data and does not offer medical advice.

17. Why This Trial Matters Statistically

This trial illustrates why an estimated difference should be read alongside its uncertainty. The point estimate alone suggests a direction, but the confidence interval includes no difference and extends to values on either side. The unadjusted p-value likewise does not meet the 0.05 threshold used in the planning illustration. Reading the estimate, interval and p-value together avoids treating a single number as a complete answer.

The study also provides a practical example of the distinction between a posted outcome result and a fully documented analysis. The registry names the primary score and reports least-squares means and a comparison, but does not report the analysis model, analysis population, missing-data approach or multiplicity plan. These details are important for understanding how robustly the displayed comparison represents the intended question. Their absence does not invalidate the result, but it limits how far the result can be assessed from the registry record.

Finally, the planning illustration makes clear that sample-size requirements depend on the effect a study aims to detect and on assumptions about allocation, significance level and statistical method. A planning calculation based on an observed effect is not the same as the original trial's design rationale, and it is not a measure of the trial's observed power. Keeping these distinctions clear helps prevent retrospective planning figures from being mistaken for a prediction of what this trial should have found.

18. 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 gives limited detail about who participated beyond the description of adult primary care patients with moderate-risk drug use. Eligibility criteria, baseline characteristics, recruitment settings and the extent to which participants reflect the broader intended population are not reported. This limits assessment of how widely the result may apply.

Masking is listed as none. For an intervention involving personalized feedback, awareness of assignment could influence participant responses or other study procedures; this is a general possibility, not evidence that bias occurred in this trial. The registry does not report whether outcome assessors were masked or provide further information about procedures intended to reduce bias. It also does not describe random-sequence generation or allocation concealment.

The primary estimate is reported as a least-squares mean comparison, but the model, covariates and analysis population are not reported. The record lists no reported analyses and does not explain missing follow-up measurements or their handling. These omissions prevent a detailed assessment of whether the analysis followed the original plan and how sensitive the estimate may be to missing data.

The primary outcome is measured at 3 month follow-up, and the same score is also listed at 6-month follow-up. The delayed group receives the computerized intervention at three-month follow-up, but the registry does not provide sufficient detail about the timing of outcome assessment relative to intervention delivery. The trial's own sample-size assumptions, rationale for enrollment and multiplicity plan are not reported. Together, these record-level gaps limit interpretation of the design and the precision and generalizability of the result.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Computerized Brief Intervention vs. Delayed Computerized Brief Intervention — NCT01936623.
• Registry record last updated 2017-07-21; status last verified 2017-04.
• Results first posted 2017-07-21.
• 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.

22. Record Summary

The registry describes a completed randomized, parallel-group study with no masking and enrollment of 80. It compared a computerized brief intervention with delayed computerized brief intervention among adult primary care patients with moderate-risk drug use. The delayed group received a substance abuse assessment at baseline and the computerized intervention at three-month follow-up.

The primary outcome was the ASSIST Global Continuum of Illicit Drug Risk Score at 3 month follow-up. The posted mean difference was 3.4 units, with a confidence interval from -2.698 to 9.498 and an unadjusted p-value of 0.274. The interval includes no difference, and the result is uncertain. A secondary entry reports the same score at 6-month follow-up. The registry does not report the analysis plan, missing-data handling, analysis population or multiplicity approach.