LINK: Aftercare Monitoring Project: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for LINK: Aftercare Monitoring Project (NCT00265512), a randomized na study. The primary outcome is Rates of Substance Use.

2. Clinical Question

The LINK: Aftercare Monitoring Project asks whether telephone case monitoring aftercare is associated with a different rate of alcohol abstinence than continuing care as usual among people receiving care for substance use disorders. The registry describes a randomized, parallel-group comparison of behavioral interventions. The primary outcome is the mean percentage of days abstinent from alcohol during a 3-month follow-up.

This question is narrower than whether either approach changes every aspect of substance use disorder recovery. The posted primary outcome is a measure of alcohol-abstinent days, not a composite measure of alcohol and drug use, treatment engagement, or long-term recovery. Psychiatric symptoms and health-related quality of life are listed as secondary outcomes, but their results are not reported in the registry record.

3. Trial Design

The registry identifies the LINK: Aftercare Monitoring Project as a randomized, parallel-group trial with no masking. Its status is completed. The sponsor is the VA Office of Research and Development. The recorded study start is 2006-11, and the primary completion is 2009-06. The phase is listed as NA.

The two behavioral arms are Telephone Case Monitoring Aftercare and Continuing Care as Usual. The registry describes the comparison as telephone case monitoring for continuing care versus face-to-face continuing care as usual, also called standard outpatient care in the brief summary. The trial's overall enrollment is 667. The posted primary-outcome results include 213 participants in the telephone-monitoring arm and 454 in the usual-care arm. Those are the arm counts attached to the reported outcome; the registry record does not explain the difference in arm sizes or provide a participant flow account.

Randomization means treatment assignment was intended to be determined by chance rather than chosen by participants or clinicians. In general, random assignment can help balance characteristics between groups, although it does not guarantee balance in a particular trial. Masking is listed as none, so the record does not describe masked treatment assignment or outcome assessment. The methods used to generate and conceal the allocation sequence are not reported in the registry record.

The registered conditions are alcohol dependence and drug dependence. The trial's primary outcome, however, is specifically the percentage of days abstinent from alcohol. The registry lists psychiatric symptoms and health-related quality of life as secondary outcomes, and indicates three outcome measures. Detailed eligibility criteria, recruitment locations, intervention fidelity procedures, and the original planned sample size are 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

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 Rates of Substance Use, measured over Rates of substance use measured at 3 months.

The primary outcome is titled “Rates of Substance Use,” but its registry description defines the reported measure as the percentage of days abstinent from alcohol. Each participant is followed for 3 months. For each participant, the number of alcohol-abstinent days is expressed as a percentage of all days in that 3-month period. The posted arm summaries report the mean of this continuous measure, in percentage of days.

This measure describes the frequency of alcohol abstinence during follow-up. A mean can summarize the average percentage across participants in an arm, while individual participants may have had different experiences. The group mean therefore does not show how outcomes were distributed among individuals, how many participants were fully abstinent, or how abstinence varied over time within the follow-up period. Those details are not reported in the registry record.

Using abstinent days creates a quantitative outcome for comparing the two assigned care approaches. It captures more variation than a simple yes-or-no status at one assessment, because participants can contribute different proportions of abstinent days. That is a general property of continuous measures, not evidence that this endpoint captures every clinically relevant aspect of substance use disorder. The posted primary measure is not a direct measure of drug abstinence, and results for the listed secondary outcomes are not reported in the registry record.

7. Results Posted in the Registry

• Telephone Case Monitoring Aftercare: mean 91.10 versus 88.00 on control; difference 3.10 (95% CI -1.89 to 8.09), standardized effect d = 0.09; z-test p = 0.223.

8. Statistical Interpretation

9. Statistical Methods Explained

The registry presents a continuous primary outcome and reports each arm's mean and standard error, followed by a mean difference, confidence interval, and unadjusted p-value. These quantities answer related but distinct questions. The means describe the observed group averages; the mean difference compares those averages; the interval describes uncertainty around that contrast; and the p-value describes compatibility with a null model under the analysis assumptions. The specific analysis procedure used to produce the inferential results is not reported in the registry record.

What does the mean describe?

The outcome is the percentage of days abstinent from alcohol during a 3-month follow-up, and the registry identifies the summary as a mean of a continuous measure. The reported mean is 91.1 for Telephone Case Monitoring Aftercare and 88.0 for Continuing Care as Usual. A mean condenses participant-level measurements into an arm-level average. It does not reveal the full distribution, the range of individual outcomes, or whether a small number of observations strongly influenced the average. Those distributional details are not reported in the registry record.

The arm-level spread is reported as a standard error: 1.79 for the telephone-monitoring mean and 1.81 for the usual-care mean. A standard error describes the estimated uncertainty in a group mean, rather than the spread of individual participant outcomes. It generally becomes smaller when a mean is estimated more precisely. It should not be interpreted as if it were the standard deviation of the participant-level outcome.

What does the mean difference compare?

The reported contrast is a mean difference of 3.1, with telephone monitoring compared against usual care. Because the outcome is a percentage of days, the contrast is expressed in percentage points. The sign depends on the order of subtraction: the reported positive value represents a higher mean in the telephone-monitoring arm. The group means and contrast describe an average difference, not a participant-by-participant comparison.

A confidence interval gives a range of values compatible with the observed estimate under the interval's statistical assumptions. The reported limits are -1.889 and 8.089. Its confidence level and the precise method used to obtain it are not reported in the registry record. In general, a narrower interval indicates greater precision, while a wider interval leaves more uncertainty about the size and direction of the contrast. An interval is not a guarantee that the true value lies within its limits.

How should the p-value be read?

The unadjusted p-value is 0.223. In general, a p-value is calculated under a null model and measures how unusual results at least as incompatible with that model would be if its assumptions held. It is not the probability that the null model is correct, and it does not tell the reader the probability that the observed contrast arose by chance in an unrestricted sense. The record does not identify the test or model used, the confidence level, or a decision threshold for the primary comparison. It also does not report an adjusted p-value.

“Unadjusted” matters because a study may assess more than one outcome or conduct more than one analysis. If multiple statistical tests are considered together, the chance of finding an apparently unusual result can change; general statistical methods address this through prespecified multiplicity procedures. The registry lists secondary outcomes, but a multiplicity plan is not reported in the registry record. Consequently, the posted p-value should not be treated as evidence that multiplicity was addressed.

What does a standardized difference add?

The reported standardized mean difference is 0.088, alongside a pooled standard deviation of 35.08. In general, standardization expresses a mean contrast relative to a measure of outcome variability, making the contrast less dependent on the original measurement units. The standardized value does not replace the mean difference in percentage points, and it does not determine clinical importance. Whether a difference matters to patients or clinicians depends on context and a meaningful threshold; no such threshold is reported in the registry record.

The comparison also reports the arm means, their standard errors, and sample sizes. The analysis population and handling of missing observations are not reported. Without those details, it is not possible to determine from the registry record whether every randomized participant contributed to the comparison, how incomplete follow-up was treated, or whether the analysis adjusted for any baseline variables. No such adjustment should be inferred from the posted summary statistics.

What can randomization and the analysis establish?

Random allocation is a design feature that can support a fair comparison by reducing systematic differences in treatment assignment. In general, the benefits of randomization depend on how allocation was generated and maintained, and on how outcomes and follow-up are handled. The record identifies the trial as randomized but does not report the sequence-generation or allocation-concealment procedures. It also records no masking. These omissions do not change the reported means, but they limit how fully the comparison methods can be assessed.

The reported statistics are not a complete account of the trial's analysis. The number of analyses is listed as 0, and no detailed analysis records accompany the outcome summary. The statistical model, assumptions, handling of protocol deviations, and any prespecified interim analyses are not reported in the registry record. The sample-size planning figures are separate planning illustrations based on the observed effect; they are not evidence about the original design or an analysis of the trial's observed statistical power.

10. Confidence Intervals and Precision

The mean difference is reported as 3.1 percentage points, with a confidence interval from -1.889 to 8.089. The estimate is a single summary of the observed contrast, while the interval communicates uncertainty about its size. Because the interval includes zero, the posted interval does not exclude a difference in either direction. Its lower limit is below zero and its upper limit is above zero.

The interval also includes values greater than the point estimate and values below it. This indicates that the data, under the interval's assumptions, do not pin down the contrast to the point estimate alone. The interval's exact confidence level and construction method are not reported in the registry record. Without that information, the limits can be described as the posted confidence interval, but should not be assigned an unreported confidence percentage or method.

The standard errors for the two arm means are 1.79 and 1.81. They describe uncertainty in the respective means, not the variability among individual participants. The pooled standard deviation is 35.08, a measure of participant-level variability used in the reported standardized contrast. Those summaries provide different information: standard errors concern precision of means, while the standard deviation concerns spread in the outcome.

Precision is not the same as importance. A precise estimate could be close to zero or could indicate a consequential contrast; an imprecise estimate can leave a broad range of effects plausible. The registry record does not report a threshold for a clinically important difference, so the interval cannot be classified against such a threshold. The results also concern the primary outcome at 3 months only; they do not provide precision estimates for longer follow-up or for the listed secondary outcomes.

11. 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. They are planning illustrations based on the observed effect, not the trial's original design assumptions. The registry record's original sample-size justification is not reported. These figures use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Each row considers an effect to detect equal to a stated fraction of the observed effect.

For 100% of the observed effect, the planning illustration gives 2,011 participants per arm for 80% power and 2,692 participants per arm for 90% power. For 75% of the observed effect, it gives 3,575 participants per arm for 80% power and 4,785 participants per arm for 90% power. For 50% of the observed effect, it gives 8,042 participants per arm for 80% power and 10,766 participants per arm for 90% power. In plain terms, the 80% column describes a planned chance of detecting the assumed effect under the listed assumptions if that effect is present; the 90% column targets a higher chance under those same assumptions.

The plotted planning relationship expresses the same idea: as the effect assumed for planning becomes smaller, more participants are needed to distinguish it from the null under the stated assumptions. The figures are not an account of what the trial observed, and this is not observed power. They do not show that the completed trial had the probability of detecting its observed result implied by any planning row. Actual trial enrollment was 667, while the planning entries are per arm and based on hypothetical effect assumptions.

12. 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 = 3.100; pooled standard deviation σ = 35.082.
2. n = 2 × (1.96 + 0.842)² × 35.082² / 3.100² = 2,010.4, rounded up to 2,011 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 <- 3.09999999999999                      # observed difference in means
sigma <- 35.0821510172908                     # 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(265512)
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 = 2,011 (80% power), 2,692 (90% power)
 75% of observed effect: n per arm = 3,575 (80% power), 4,785 (90% power)
 50% of observed effect: n per arm = 8,042 (80% power), 10,766 (90% power)
power.t.test: 2011.4 
Simulated power at n = 2,011 per arm: 0.801 (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.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists psychiatric symptoms and health-related quality of life as secondary outcomes, and indicates three outcome measures. The primary outcome is the percentage of days abstinent from alcohol at 3 months. Results for the secondary outcomes are not reported in the registry record. The number of analyses is listed as 0, and a detailed analysis plan is not reported.

When a study evaluates several outcomes or statistical comparisons, multiplicity can affect the chance of obtaining at least one result that appears unusual under a null model. A prespecified adjustment or hierarchy can address that issue, but no such procedure is reported in the registry record. The posted p-value for the primary comparison is explicitly unadjusted. It should not be assumed that any correction was or was not performed beyond what the registry states.

Missing data handling is not reported in the registry record. The record does not state how participants with no 3-month measurement, partial follow-up, or incomplete daily abstinence information were handled. It also does not provide the number of missing primary-outcome observations or reasons for missingness. These details are important because an analysis of observed measurements may represent a different set of participants from the randomized group if follow-up is incomplete.

The primary analysis population is not reported in the registry record. It is therefore not possible to tell whether the comparison included all randomized participants according to assigned arm, only participants with outcome data, or another defined group. The record also does not report whether any participants were excluded after randomization, how protocol deviations were handled, or whether the analysis adjusted for baseline characteristics. Those choices should not be inferred from the arm counts alone.

Interim analyses and stopping rules are not reported in the registry record. Nor does the record give enough detail to assess prespecification of the analysis, the treatment of multiple outcome time points, or whether further analyses were conducted but not entered. These are limitations in what the registered results disclose; they do not by themselves establish that a particular method was or was not used.

14. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: hosapitalizations (28.2%).

The registry's serious-adverse-event summary reports 60 participants affected in the Telephone Case Monitoring Aftercare arm, with 213 at risk, and 92 affected in the Continuing Care as Usual arm, with 454 at risk. These are counts as recorded, not calculated event rates. The registry also reports zero participants at risk and zero affected for other adverse events in both arms, and zero deaths in both arms.

These entries should be read as registry summaries, not as evidence that an intervention caused or prevented an event. The record does not describe event ascertainment, follow-up duration for the safety summary, severity criteria, or the relationship of events to treatment. It also does not explain why the other-adverse-event fields show zero participants at risk. The serious-event counts alone therefore do not permit a complete comparison of safety between arms.

The listed serious-event term is recorded as “hosapitalizations” at 28.2%. The denominator and the exact basis for that percentage are not reported in the registry record, so it should not be interpreted as a participant-level rate or compared with the arm counts. These safety figures are distinct from the primary efficacy outcome, which measures alcohol-abstinent days.

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

The posted primary outcome shows mean alcohol-abstinent days, expressed as a percentage of days during 3-month follow-up, of 91.1 in the telephone-monitoring arm and 88.0 in the usual-care arm. The reported mean difference is 3.1 percentage points, with a confidence interval from -1.889 to 8.089 and an unadjusted p-value of 0.223. Taken together, these statistics describe a higher observed average in the telephone-monitoring group, while leaving uncertainty about the direction and size of the underlying difference.

The result does not establish that telephone case monitoring works or does not work. A point estimate is not a definitive account of the effect, and a p-value is not a measure of the probability that an intervention is effective. The confidence interval includes zero and a range of positive values. The registry does not report a threshold for a clinically meaningful change, so the estimates cannot be classified against such a threshold from the record alone.

The endpoint also has a limited scope. It concerns alcohol abstinence, rather than all substance use, drug abstinence, psychiatric symptoms, quality of life, or treatment engagement. Although psychiatric symptoms and health-related quality of life are listed as secondary outcomes, their results are not reported in the registry record. The primary assessment is at 3 months, so the result does not describe longer-term outcomes.

Randomization is a useful design feature for comparing assigned groups, but the record does not report allocation procedures, the primary analysis population, or the handling of missing outcomes. Those details affect how the posted comparison should be interpreted. The results are best understood as a registry-reported comparison of the arm means and their uncertainty, with important questions about analysis and follow-up left unanswered.

16. Why This Trial Matters Statistically

The registry's brief summary places the trial in a continuing-care context: it states that duration of treatment is consistently associated with positive addiction-treatment outcomes and that 36% of VA substance use disorder treatment programs meet the continuing-care performance criterion specified by the Office of Quality Performance. Those statements describe the context recorded for the study; they are not findings from the trial's primary comparison.

Statistically, the trial illustrates the distinction between an observed difference and a precise estimate of that difference. The arm means differ by 3.1 percentage points, but the confidence interval extends from -1.889 to 8.089. Reporting both the point estimate and uncertainty is essential: the mean difference alone would conceal how much uncertainty remains, while the interval makes clear that multiple underlying contrasts remain compatible with the posted results.

The outcome also illustrates why measurement definitions matter. The title refers broadly to rates of substance use, but the operational measure is the percentage of days abstinent from alcohol at 3 months. Readers should interpret findings according to the measured endpoint rather than extending them to all substance-related outcomes. The registry's secondary-outcome listings also remind readers to consider multiplicity, while the absence of a reported adjustment plan limits assessment of that issue.

Finally, the sample-size illustrations distinguish planning from post-trial interpretation. They estimate participants per arm under stated assumptions and different assumed fractions of the observed effect. They are not a substitute for the trial's unreported original design rationale, nor do they establish the power of the completed study. This separation helps prevent planning calculations from being mistaken for evidence about the result.

17. 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 measure concerns alcohol abstinence during a 3-month period. It does not directly report drug abstinence, later outcomes, or the secondary outcomes of psychiatric symptoms and health-related quality of life. Results for those secondary outcomes are not reported in the registry record. The mean summary also does not describe the distribution of individual participants' abstinent-day percentages.

The trial is recorded as having no masking. The registry does not report how the primary outcome was collected or whether outcome assessment could be influenced by knowledge of assignment. The allocation-generation and concealment methods are also not reported in the registry record. These missing design details constrain assessment of possible sources of bias but do not establish that bias occurred.

The posted arm counts are 213 and 454, while overall enrollment is 667. The record does not explain the arm-count difference, provide participant flow, or specify whether those counts represent everyone randomized or only participants included in the outcome summary. Missing-data procedures, reasons for incomplete follow-up, and the primary analysis population are not reported.

The confidence level and method for the reported interval are not reported, and the detailed statistical model is not specified. The p-value is unadjusted; no multiplicity plan is reported despite the listed secondary outcomes. The registry also does not report a clinical-importance threshold, the original sample-size justification, or detailed eligibility criteria. These limitations concern information available in the registry record and should be kept distinct from the outcome estimates that it does report.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: LINK: Aftercare Monitoring Project — NCT00265512.
• Registry record last updated 2019-01-16; status last verified 2018-07.
• Results first posted 2014-10-17.
• 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.

21. Record Summary

NCT00265512, titled LINK: Aftercare Monitoring Project, is a completed, randomized, parallel-group behavioral trial with no masking. The sponsor is the VA Office of Research and Development. The recorded study start is 2006-11, and primary completion is 2009-06. Enrollment is 667; the registered conditions are alcohol dependence and drug dependence.

The primary outcome is the mean percentage of days abstinent from alcohol at 3 months. The posted means are 91.1 for Telephone Case Monitoring Aftercare and 88.0 for Continuing Care as Usual. The reported mean difference is 3.1, with a confidence interval from -1.889 to 8.089 and an unadjusted p-value of 0.223. The registry also lists psychiatric symptoms and health-related quality of life as secondary outcomes, but their results are not reported in the registry record.