Depression Outpatient Cardiology Screening Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Depression Outpatient Cardiology Screening Study (NCT01552889), a randomized na study. The primary outcome is Beck Depression Inventory 2.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group study with single masking, registered as completed. The registry lists enrollment of 201 participants: 101 in usual care and 100 in collaborative care. Randomization indicates that assignment was by chance, but the method used to generate or conceal the allocation is not reported in the registry record. The identity of the party or parties masked is also not reported, so “single” should not be read as specifying who was unaware of assignment.

The study began in 2012-01, and primary completion is listed as 2016-07. These dates describe the registry record; they do not establish the timing of each participant’s follow-up or the duration of recruitment. The sponsor was Washington University School of Medicine. The study is listed without an applicable phase.

The comparison was between a collaborative screening and case-management approach and usual care outside the study. The available description identifies brief screening, consultative, and referral services, with the patient, primary care physician, cardiologist, and nurse case manager involved. It does not report the full intervention manual, the frequency of contacts, or treatment adherence. The usual-care description likewise does not specify a common clinical pathway.

The primary endpoint was a continuous score measured at 12 months. The registry record lists the two arm-level means and standard deviations, but no reported outcome analyses. It does not state the trial’s original statistical analysis plan, its original sample-size assumptions, or the analysis population. Those omissions limit what can be concluded about how the posted summaries relate to the investigators’ prespecified analysis.

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 Beck Depression Inventory 2, measured over 12 months.

The primary endpoint was the Beck Depression Inventory 2, a self-report inventory of depression symptoms. The stated score range is 0-63, with higher scores indicating more symptoms. The registry description says that a score of 12 or greater is considered to indicate clinically significant depression. This threshold describes the instrument’s stated interpretation; the posted group means do not show how many participants were above or below it.

The endpoint was collected at 12 months and summarized as a mean with a standard deviation in each arm. A mean describes the average score in the group, while the standard deviation describes variation in individual scores around that average. The mean comparison therefore addresses the average symptom-score difference between randomized groups at that follow-up point. It does not provide the distribution of scores, the proportion crossing the stated threshold, or individual-level change from baseline.

A continuous symptom score can retain information across its range rather than reducing outcomes to a yes-or-no category. That makes it useful for comparing average reported symptom burden. However, interpreting an average requires attention to the scale, the variability, and the uncertainty around the between-group estimate. The registry record does not report baseline scores or a baseline-adjusted result, so the posted outcome summaries should not be interpreted as changes from baseline.

7. Results Posted in the Registry

• Collaborative Care (CC): mean 15.90 versus 17.40 on control; difference -1.50 (95% CI -3.96 to 0.96), standardized effect d = -0.17; z-test p = 0.232.

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.

Treatment Satisfaction Scale.

• 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 deviations.
• Result:
  • Collaborative Care: mean 4.00 versus 3.30 on control; difference 0.70 (95% CI 0.37 to 1.03), standardized effect d = 0.58; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Collaborative Care than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

PROMIS Physical Functioning Scale 10a Short Form

• 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 deviations.
• Result:
  • Collaborative Care: mean 39.20 versus 39.60 on control; difference -0.40 (95% CI -1.70 to 0.90), standardized effect d = -0.09; z-test p = 0.547.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Collaborative Care and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes give a broader view of the outcomes registered for follow-up: treatment satisfaction and physical functioning, both measured at 12 months. Their overall direction is not uniform. The posted satisfaction comparison points toward higher scores in the collaborative-care group, while the physical-functioning estimate points slightly toward usual care. The primary depression-score estimate also points toward a lower average score in collaborative care. The summaries therefore do not show a consistent direction across all measures.

These outcomes address different constructs. Treatment satisfaction concerns participants’ reported satisfaction, while the PROMIS measure concerns physical functioning. They should not be treated as interchangeable measures of depression symptoms or as direct confirmation of the primary endpoint. A pattern in one measure cannot establish a corresponding effect on another, particularly when the measures capture distinct aspects of participants’ experience.

The registry record lists two secondary outcomes and reports unadjusted comparisons, but it does not report a multiplicity procedure or a hierarchy for interpreting those outcomes. When several outcomes are examined, the chance of obtaining a seemingly notable result by chance can increase. This general concern is one reason isolated secondary findings generally carry less weight than a prespecified primary result, especially when no adjustment plan or detailed analysis plan is available.

The registry record reports no outcome analyses for the secondary measures. The posted summaries and recalculated comparisons therefore do not document whether the investigators treated these outcomes as confirmatory, exploratory, or adjusted for other variables. These results can be considered descriptive context for the primary result, but their inferential strength is limited by the absence of a reported analysis plan and multiplicity handling. They do not resolve the uncertainty around the primary comparison.

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

• Treatment Satisfaction Scale.
• PROMIS Physical Functioning Scale 10a Short Form

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous: it is a score on a scale, rather than a count of events or a binary classification. The registry reports a mean and standard deviation for each randomized group. This form of summary gives a central value and a measure of how dispersed participant scores are around that value. The standard deviation is not the uncertainty in the mean; it describes variation among the scores themselves.

What does a mean difference represent?

The posted comparison subtracts the usual-care mean from the collaborative-care mean. The resulting estimate is -1.5 units. This is an unadjusted difference in group averages, expressed in the same units as the Beck Depression Inventory 2. Its direction is interpreted using the scale description: higher scores correspond to more reported depression symptoms. The estimate is not a difference in the percentage of participants with clinically significant scores, nor is it an estimate of within-person change.

General explanation: a mean difference is most directly interpretable when the outcome scale and its direction are clear. Its numerical size should be considered alongside the scale’s meaning and the variability of individual observations. A group-average comparison can conceal variation in individual responses, including participants whose scores are above or below the group mean.

What does the confidence interval add?

The posted interval runs from -3.961 to 0.961. A confidence interval describes the uncertainty around an estimated effect under the assumptions of the method used to construct it. The interval includes zero, which means the posted range includes no difference as well as values on either side of zero. The confidence level and the specific interval method are not reported in the registry record, so they cannot be specified from the posted information.

General explanation: an interval is not a list of the outcomes that individual participants experienced, and it does not guarantee that the true effect lies within its endpoints. It is a way to express how precisely an estimate has been measured under a statistical model. Wider intervals indicate greater uncertainty than narrower intervals, all else equal. The interpretation also depends on the design and analysis assumptions underlying the interval.

How should the p-value be read?

The primary comparison has an unadjusted p-value of 0.232. A p-value describes how unusual data at least as incompatible with a specified null model would be if that model and the analysis assumptions held. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. Because the registry record lists no reported outcome analyses, the posted p-value should not be mistaken for a documented sponsor analysis or a reported prespecified test.

General explanation: the distinction between statistical evidence and practical meaning matters. A p-value alone does not tell readers whether an estimate is clinically important, whether the study was designed to detect a particular effect, or whether the result will generalize beyond the enrolled setting. Interpretation should consider the effect estimate, its interval, the outcome scale, and the completeness of the analysis record.

What does “unadjusted” mean in this context?

The posted comparison is a simple comparison of the arm-level summaries, without a reported adjustment for baseline scores or other variables. The registry record does not describe a model incorporating covariates, stratification factors, or repeated measurements. An unadjusted comparison can be useful as a description of the reported group difference, but it may not match an analysis specified in a protocol or statistical analysis plan. Such a plan is not reported in the registry record.

The comparison is labelled as recalculated from posted summary statistics. The registry record does not report a sponsor outcome analysis, and there is no recorded discrepancy between the posted summaries and this recalculation. These figures therefore describe a simple reconstruction from the group means and associated summaries; they should not be represented as the investigators’ own adjusted or prespecified analysis.

Why can variation matter?

General explanation: when continuous outcomes vary substantially among participants, the group mean alone gives an incomplete picture. Greater variability can make a mean difference less precisely estimated, while a larger number of observations can generally improve precision under appropriate assumptions. The standard deviations describe score variation, but the registry record does not give participant-level observations, distributions, or details of missing outcome data. It is therefore not possible to assess the shape of the score distributions or evaluate the sensitivity of the result to unusual values.

General explanation: over-dispersion is especially relevant to count outcomes when observed variability exceeds what a simple count model expects. The primary endpoint in this trial is a continuous score, not a count outcome, and the registry record does not report an over-dispersion analysis. A count-model explanation would not be a basis for interpreting this primary result.

Finally, the number of outcomes and the existence of multiple comparisons can affect how confidently individual p-values should be interpreted. The registry lists a primary outcome and two secondary outcomes but does not report a multiplicity strategy. Without that information, the posted unadjusted comparisons are descriptive statistical evidence rather than a complete account of confirmatory testing.

11. Confidence Intervals and Precision

The primary mean difference is -1.5 units, with a confidence interval from -3.961 to 0.961. This interval is important because the point estimate alone does not show how uncertain the comparison is. The range includes zero and values on either side, so the posted summaries do not pin down a single direction or magnitude of the average difference with high precision. The confidence level and interval construction method are not reported in the registry record.

Precision depends on the amount of information in the data and on variability. The two arm summaries include 101 participants in usual care and 100 in collaborative care, with standard deviations of 9.0 and 8.8. These standard deviations describe variation in scores, not uncertainty in the group means. Participant-level data and information about missing outcomes are not reported, so further assessment of precision or distributional features is not possible from the registry summaries alone.

The interval should not be read as proving that all values inside it are equally plausible, or that values outside it are impossible. General explanation: a confidence interval is a statistical procedure for expressing uncertainty under a model and its assumptions. Its interpretation depends on the chosen confidence level, method, and analysis; those details are not specified in the registry record. The interval’s inclusion of zero means the posted range is compatible with no average difference, but it does not establish equivalence between the groups.

Precision and clinical importance are also separate questions. The scale description provides a threshold of 12 or greater for a clinically significant score, but the group means and mean-difference interval do not indicate how many participants crossed that threshold. The posted result concerns average scores, and the registry record does not report a threshold-based comparison.

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. They are illustrations based on the observed effect, not a report of the trial’s original design calculation. The planning assumptions listed are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Each row considers detecting the stated fraction of the observed effect. The original design assumptions and sample-size justification are not reported in the registry record.

For the primary Beck Depression Inventory 2 comparison, planning for 100% of the observed effect gives 553 participants per arm for 80% power and 740 participants per arm for 90% power. Planning for 75% of the observed effect gives 983 participants per arm for 80% power and 1,316 participants per arm for 90% power. Planning for 50% of the observed effect gives 2,212 participants per arm for 80% power and 2,960 participants per arm for 90% power.

In plain language, 80% power means that, under the stated planning assumptions and if the assumed effect is the true effect, the design would have an 80% chance of detecting an effect at the specified significance level. The 90% column describes the corresponding chance as 90%. These are properties of hypothetical designs under assumptions, not probabilities that the observed result is correct. The listed participant counts are per arm for this continuous outcome.

The smaller the effect a study aims to detect, the more participants it generally requires under otherwise similar assumptions. That pattern is reflected in the larger planning counts for smaller fractions of the observed effect. These numbers are not observed power for the completed trial; observed power is not an interpretation of the posted outcome result. The figures are planning illustrations only, based on the effect estimate recorded for the outcome.

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 = -1.500; pooled standard deviation σ = 8.901.
2. n = 2 × (1.96 + 0.842)² × 8.901² / -1.500² = 552.8, rounded up to 553 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 <- -1.5                      # observed difference in means
sigma <- 8.90106424668523                     # 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(1552889)
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 = 553 (80% power), 740 (90% power)
 75% of observed effect: n per arm = 983 (80% power), 1,316 (90% power)
 50% of observed effect: n per arm = 2,212 (80% power), 2,960 (90% power)
power.t.test: 553.7 
Simulated power at n = 553 per arm: 0.800 (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 lists one primary outcome and two secondary outcomes, all with a 12-month timeframe. The record does not report whether the investigators planned to adjust for testing multiple outcomes, whether any outcome hierarchy was specified, or whether secondary analyses were considered exploratory. A multiplicity strategy is not reported in the registry record. Consequently, the unadjusted secondary p-values should not be interpreted as though a family-wise testing plan or another adjustment had been applied.

The record lists zero reported analyses. It includes arm-level outcome summaries and simple recalculated comparisons, but does not document a sponsor analysis, a prespecified statistical model, or adjustments for baseline values. The original statistical analysis plan, analysis populations, and handling of protocol deviations are not reported in the registry record. It is therefore not possible to determine whether the posted summaries reflect an intention-to-treat population, a per-protocol population, or another analysis set.

The primary outcome summaries list 101 participants in usual care and 100 in collaborative care. The registry does not explain how those outcome counts were obtained, whether any observations were missing, how missing measurements were handled, or whether imputation or another method was used. The listed group counts alone do not establish the completeness of follow-up or the absence of missing data.

These omissions matter because different analysis choices can affect the estimate and its uncertainty. General explanation: prespecified methods help readers distinguish planned analyses from choices made after results are known, while missing-data procedures clarify what population the estimate represents and what assumptions support it. The registry record does not provide enough information to evaluate those issues. This limits the inferential detail that can be attached to the posted comparisons, without changing what the arm-level summaries themselves report.

15. 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.

The registry’s safety summary lists zero participants with serious adverse events in usual care among 101 at risk and zero in collaborative care among 100 at risk. It also lists zero participants with other adverse events in each arm, using the same at-risk counts. No serious adverse-event terms are listed.

Deaths are recorded separately: 8 in the usual-care group and 1 in the collaborative-care group. These are counts in the registry safety summary. The record does not give further detail about timing, causes, relationship to study participation, or whether deaths were included in another adverse-event category. The counts should not be treated as evidence that the intervention caused or prevented deaths.

These figures describe what the registry record lists; they do not provide a complete clinical narrative of safety monitoring. The duration of safety follow-up, the definitions used for adverse-event categories, and the process for collecting events are not reported in the registry record. Zero listed events should therefore be read as the posted count, not as proof that no events occurred outside the recorded categories or observation period.

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

The primary result is an estimate of the average difference in depression symptom scores at 12 months between randomized groups. The collaborative-care mean was numerically lower than the usual-care mean, and the unadjusted mean difference was -1.5 units. The confidence interval extends from -3.961 to 0.961, so the range includes no average difference as well as differences in either direction. The unadjusted p-value is 0.232.

This result does not establish that the groups were equivalent. A result that does not meet a conventional statistical threshold is not proof that there is no effect; the interval expresses uncertainty about the possible magnitude and direction. Conversely, the numerical direction of the point estimate is not proof of a benefit or of a clinically important difference. The registry record does not report a prespecified equivalence margin or a clinical-importance threshold for the between-group mean difference.

The Beck Depression Inventory 2 description states that a score of 12 or greater indicates clinically significant depression. The group means do not reveal how many individuals met that threshold, and no threshold-based outcome is posted. They also do not show how participants’ scores changed from baseline, because baseline summaries and within-person change results are not reported.

The trial compares the collaborative approach as a package with usual care. It cannot isolate the contribution of screening, consultation, referral, or coordination with clinicians. The registry record also does not provide enough detail about usual care, adherence, or the full intervention delivery to identify which aspects of care may explain the observed summaries.

Accordingly, the posted data describe group averages at a specified follow-up time, with substantial uncertainty around the primary comparison. They do not settle questions about individual outcomes, threshold-defined depression, change over time, or the effect of each intervention component. No medical recommendation follows from these registry summaries alone.

17. Why This Trial Matters Statistically

This trial is statistically instructive because it separates a numerical difference from the certainty and meaning of that difference. The primary estimate has a direction, a magnitude, an interval, and an unadjusted p-value; none of these elements should be interpreted in isolation. The confidence interval includes zero, and the p-value is 0.232, while the point estimate alone might invite an overly simple directional reading.

The outcome is a continuous symptom scale with a stated threshold for clinically significant scores. That distinction highlights why an average difference is not interchangeable with a comparison of the proportion above a threshold. The registry record reports means and standard deviations, not the number of participants meeting the threshold. The available analysis therefore answers an average-score question, not every clinically relevant question that could be asked of the scale.

The record also illustrates the importance of transparent analysis reporting. The randomized groups and outcome summaries are documented, but the registry lists no reported outcome analyses and does not describe the original analysis plan, missing-data approach, or multiplicity handling. Without those details, readers can interpret the posted estimates but cannot establish how they relate to prespecified analyses or assess all assumptions behind the reported comparisons.

Finally, planning illustrations based on the observed effect are distinct from a trial’s original sample-size justification. The registry’s planning figures describe hypothetical designs under stated assumptions; they do not show the design rationale used before enrollment or convert the completed study into a statement about observed power. Keeping these distinctions clear supports a more careful reading of both the results and their limits.

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 leaves several trial-specific details unavailable. It does not report the randomization method, allocation concealment, or who was masked. Although the design is labeled single-masked, the masked party is not identified. Those omissions limit the assessment of how assignment and awareness of treatment may have affected conduct or outcome reporting.

The intervention description identifies screening, consultation, referral, and collaboration among the patient, primary care physician, cardiologist, and nurse case manager. It does not provide the full content of the intervention, its intensity, adherence, or the duration of contacts. The description of usual care is also broad and does not indicate how care varied across participants. The contrast between the arms may therefore be difficult to characterize beyond the registry’s stated descriptions.

Only the 12-month outcome summaries are posted for the primary endpoint. Baseline scores, other follow-up measurements, participant-level score distributions, and threshold counts are not reported in the registry record. The reported arm counts do not explain missing observations or exclusions, and the missing-data procedure is not reported.

The record lists no reported outcome analyses. It does not state the original statistical plan, analysis population, multiplicity approach, or original sample-size justification. Thus the posted unadjusted comparisons may not capture every analysis considered by the investigators, but no alternative sponsor analysis is reported. The registry also gives limited detail about adverse-event definitions, timing, and causes of death. These gaps constrain interpretation of the posted results rather than changing the numerical summaries themselves.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Depression Outpatient Cardiology Screening Study — NCT01552889.
• Registry record last updated 2017-04-27; status last verified 2017-03.
• Results first posted 2017-04-27.
• 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 completed Depression Outpatient Cardiology Screening Study was a randomized, parallel-group, single-masked trial with 201 participants. It compared collaborative depression screening and case-management services with usual care among cardiology outpatients with documented coronary heart disease. The primary outcome was the Beck Depression Inventory 2 score at 12 months.

The posted primary mean difference was -1.5 units, with a confidence interval from -3.961 to 0.961 and an unadjusted p-value of 0.232. Two secondary outcomes were also posted. The registry record lists no reported outcome analyses and does not report the original analysis plan, missing-data methods, or multiplicity approach. Safety counts include no listed serious or other adverse events in either arm and deaths recorded as 8 in usual care and 1 in collaborative care.