Cognitive Behavior Therapy and Work Outcome: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Cognitive Behavior Therapy and Work Outcome (NCT00810355), a randomized na study. The primary outcome is Work Quality.

2. Clinical Question

3. Trial Design

The registry describes a randomized, single-masked, parallel-group study with three arms: support group, Cognitive Behavior Therapy, and Cognitive Behavior Therapy combined with Cognitive Remediation. The listed condition is schizophrenia. The study is marked completed, and the registry lists enrollment as 87. Its start date is 2009-10-01 and its primary completion date is 2015-08-06.

The posted primary outcome summaries report 25 participants for each arm. These outcome-summary counts are not the same as the registry's enrollment entry; the registry record does not explain the distinction. The record does not identify who was masked, how randomization was carried out, or whether additional design features were used.

The primary outcome was Work Quality at six months. It is a continuous score, reported as a mean with standard deviation. The registry states that the Work Behavior Inventory score is the total average of five subscales, ranges from 1-5, and assigns higher scores to better work performance.

The intervention descriptions identify the three groups but do not report treatment schedules, duration or intensity of sessions, adherence, or other implementation details. Phase is listed as NA. The registry record does not report a sample-size justification, the trial's original statistical plan, or interim analyses. Those absences limit how much can be inferred about the trial's planning and conduct beyond the design features explicitly recorded.

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 Work Quality, measured over 6 months.

The primary endpoint is Work Quality, measured at six months as the average work-performance score on the Work Behavior Inventory. The score is the total average of five subscales, with values ranging from 1-5; higher scores represent better work performance. The posted summaries express this continuous measure as a mean and standard deviation for each arm.

A measure of work performance is relevant to the study's stated purpose because the research concerns the effects of the behavioral interventions on work for people with schizophrenia. A continuous score can describe the average level of performance in each group and support comparisons of group means. It does not, by itself, describe how many participants improved, how consistent any change was within individuals, or whether a score difference was important in daily life.

The registry record identifies this as the primary measure and gives its timeframe, scale, and direction. It does not report a threshold for a meaningful difference, a minimum important change, or further details about how scores were collected. The interpretation therefore remains tied to the reported scale and group averages, rather than to an unreported clinical threshold.

7. Results Posted in the Registry

• Cognitive Behavior Therapy: mean 3.23 versus 3.01 on control; difference 0.22 (95% CI 0.03 to 0.41), standardized effect d = 0.65; z-test p = 0.022.
• Cognitive Behavior Therapy and Cognitive Remediation: mean 3.33 versus 3.01 on control; difference 0.32 (95% CI 0.12 to 0.52), standardized effect d = 0.90; z-test p = 0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The outcome is continuous, so the registry reports an average score and standard deviation for each arm. A mean gives the center of the observed scores, while a standard deviation describes how dispersed individual scores are around that mean. These summaries are useful for comparing groups, but they do not show the full distribution, possible outliers, or how scores changed within individual participants.

What does a mean difference represent?

A mean difference expresses the difference between two group averages in the units of the outcome scale. Here, each posted comparison uses the support group as the reference. The estimate of 0.22 compares Cognitive Behavior Therapy with support group, and the estimate of 0.32 compares Cognitive Behavior Therapy with Cognitive Behavior Therapy plus Cognitive Remediation against support group. These are unadjusted comparisons based on the posted summary statistics. They are not adjusted for other characteristics or for any additional structure not represented in the summaries.

How should the p-values be read?

A p-value describes how compatible the observed data are with a specified null hypothesis under the assumptions of the statistical test. It is not the probability that the null hypothesis is true, nor does it measure the size or practical importance of a difference. The posted unadjusted p-values are 0.022 and 0.001 for the two comparisons with support group. The registry record does not report a multiplicity procedure, so these should not be interpreted as adjusted for testing more than one comparison.

What does a confidence interval add?

A confidence interval gives a range of values compatible with the estimate under the method's assumptions and conveys sampling uncertainty. It is more informative than a point estimate alone because it shows the range of differences that remain plausible under that calculation. For both posted comparisons, the interval lies above zero. That does not ensure that the effect is important in practice, and a confidence interval is not a range containing every participant's response. The registry record does not report whether the intervals arise from the trial's own prespecified model or another analysis approach; the posted comparisons are unadjusted summary-statistic calculations.

Why do standard deviations matter?

Standard deviations describe variation among scores, whereas standard errors and confidence intervals describe uncertainty in estimated quantities such as a mean or mean difference. They answer different questions. A relatively narrow spread among observed scores does not by itself guarantee a precise comparison, since precision also depends on the amount of information available and on the analysis. In this record, the arm standard deviations are 0.33, 0.35, and 0.38.

More generally, statistical methods must account for features such as clustering, repeated measurements, or over-dispersion when those features are present. Over-dispersion means that observed variability exceeds what a model assumes; ignoring it can make uncertainty estimates too small. These are general considerations, not claims that such features were present in this study. The registry record does not describe whether scores were repeated, clustered, or analyzed with a model that addressed such features.

What can randomization support?

In general, random assignment is intended to make treatment groups comparable on average, including with respect to characteristics that were not measured. It does not ensure that groups are identical, nor does it remove uncertainty or problems caused by missing outcomes or deviations from assigned interventions. The registry labels allocation as randomized but does not report the sequence-generation or concealment procedures. The single-masked designation is recorded, but who was masked is not reported in the registry record.

Statistical methods also depend on the population included in the analysis and on how missing outcome values are handled. The registry record does not report an analysis population, missing-data approach, covariate adjustment, or model specification. Therefore, the posted group summaries and comparisons support a focused description of the six-month score differences, but not a reconstruction of the full trial analysis.

10. Confidence Intervals and Precision

The mean difference for Cognitive Behavior Therapy versus support group is 0.22 points on the Work Behavior Inventory scale. Its 95% confidence interval lies above zero, with a lower endpoint of 0.031 and an upper endpoint of 0.409. The mean difference for Cognitive Behavior Therapy with Cognitive Remediation versus support group is 0.32 points; its 95% confidence interval also lies above zero, with a lower endpoint of 0.123 and an upper endpoint of 0.517. These endpoints are recorded with more than three decimal places, so they are not reproduced. The posted estimates and intervals are unadjusted.

A confidence interval communicates statistical precision: a narrower interval indicates less uncertainty about the estimated difference than a wider interval, under the assumptions used to calculate it. Neither interval represents the range of scores for individual participants. Both intervals exclude zero, but that feature alone does not establish whether the differences are important in practical terms. The registry record does not report a threshold for interpreting the size of a difference.

The outcome summaries list 25 participants in each arm. The registry's enrollment field is 87, and the record does not explain how that enrollment entry relates to the arm counts in the outcome summaries. The registry record also does not report missing-data handling or further analysis details. These omissions matter because the precision and interpretation of a comparison depend on which outcomes contributed to it and how the data were analyzed.

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 sample-size illustrations are planning calculations based on the observed mean differences, not the trial's original design assumptions. They use a two-sided significance level of 0.05, equal allocation between the two compared arms, and a normal approximation. Each planning row uses the stated fraction of the observed effect: 100%, 75%, or 50%. The figures are participants per arm, not total participants or total events.

The 80% power column gives the estimated participants per arm for a future study to have an 80% chance of detecting the specified effect under those assumptions. The 90% power column gives the participants per arm for a 90% chance under the same planning framework. These are design illustrations, not observed power for this trial.

For the comparison of Cognitive Behavior Therapy with support group, planning for 100% of the observed effect gives 38 participants per arm for 80% power and 51 for 90% power. Planning for 75% gives 67 and 90 participants per arm, respectively; planning for 50% gives 151 and 201.

For the comparison of Cognitive Behavior Therapy with Cognitive Remediation against support group, planning for 100% of the observed effect gives 20 participants per arm for 80% power and 26 for 90% power. Planning for 75% gives 35 and 47 participants per arm, respectively; planning for 50% gives 78 and 104. Smaller effects require more participants to detect under the stated assumptions. The trial's own original design assumptions are not reported in the registry record.

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 = 0.220; pooled standard deviation σ = 0.340.
2. n = 2 × (1.96 + 0.842)² × 0.340² / 0.220² = 37.5, rounded up to 38 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 <- 0.22                      # observed difference in means
sigma <- 0.340147027033899                     # 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(810355)
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 = 38 (80% power), 51 (90% power)
 75% of observed effect: n per arm = 67 (80% power), 90 (90% power)
 50% of observed effect: n per arm = 151 (80% power), 201 (90% power)
power.t.test: 38.5 
Simulated power at n = 38 per arm: 0.792 (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 three outcome measures and no posted secondary outcomes. The reported results focus on the primary Work Quality outcome and include two comparisons against the support group. The registry record does not report a multiplicity adjustment, a hierarchy for testing outcomes, or a prespecified strategy for interpreting multiple comparisons. The posted p-values are unadjusted, so they describe each comparison individually rather than controlling the chance of false-positive findings across a family of tests.

The registry record reports zero analyses in its analyses field, but it does contain group summaries and calculated pairwise comparisons. It does not report the trial's original statistical analysis plan, analysis population, covariate adjustment, model specification, or whether any analyses were prespecified. Accordingly, the posted comparisons should not be treated as evidence about unreported adjusted or model-based analyses.

Missing-data handling is not reported in the registry record. The record does not state whether all participants with an outcome were included, how unavailable six-month scores were handled, or whether any sensitivity analyses were conducted. The arm summaries list 25 participants each, while the overall enrollment field lists 87; the registry record does not explain the relationship between these entries. This prevents a reader from determining from the record alone how the reported outcome counts relate to the full enrollment.

The record also does not report whether analyses followed assigned groups regardless of intervention exposure, or whether another population definition was used. These details can affect the interpretation of randomized comparisons. Without them, the reported estimates can be described as posted unadjusted comparisons of arm summaries, but not as a complete account of the trial's statistical analysis procedures.

14. 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.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: psychiatric hospitalization (4.0%).

The serious adverse event summaries list 25 participants at risk in each arm. One serious adverse event is recorded in the support group, none in the Cognitive Behavior Therapy group, and one in the Cognitive Behavior Therapy plus Cognitive Remediation group. The listed top serious-event term is psychiatric hospitalization, reported as 4.0%. The record does not provide enough detail in these summaries to attribute that term to a specific arm or to establish the relationship between the term and the group-level counts.

No other adverse events are recorded in the summaries for any arm. Death counts are not reported in the registry record. These counts are descriptive; they do not establish whether an intervention caused an event or whether event rates differ meaningfully between groups. The small arm-level counts and the absence of further event details limit comparisons. The registry record does not report event timing, severity beyond the serious-event designation, or additional context for interpreting individual events.

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

The posted results show higher six-month average Work Behavior Inventory scores in both treatment arms than in the support group. The mean was 3.23 with Cognitive Behavior Therapy and 3.33 with Cognitive Behavior Therapy plus Cognitive Remediation, compared with 3.01 in the support group. The reported unadjusted mean differences were 0.22 and 0.32, respectively, and both confidence intervals lie above zero.

These findings describe average scores on one work-performance measure at one follow-up time. They do not show how many participants experienced a change, whether a difference was noticeable or important to participants, or whether scores remained different beyond six months. The registry does not report a threshold for meaningful change or results for later follow-up.

The results also do not establish why the means differed. The registry record does not describe implementation, adherence, or the separate contribution of Cognitive Remediation beyond the reported comparison of the combined arm with support group. It does not report a direct comparison of the combined intervention with Cognitive Behavior Therapy alone. Therefore, the posted comparisons do not establish whether adding Cognitive Remediation changed the outcome relative to Cognitive Behavior Therapy alone.

Randomization is an important design feature, but interpretation also depends on the trial's analysis population, missing-data approach, and other design and analysis details. Several of these are not reported in the registry record. The estimates should therefore be understood as the posted group summaries and unadjusted comparisons, rather than as a complete account of every factor that may affect inference.

The serious adverse event summaries record one event in the support group, none in the Cognitive Behavior Therapy group, and one in the combined-treatment group. Those counts are descriptive and do not establish comparative safety. Overall, the registry results characterize differences in a specific score at a specified time; they do not support claims about outcomes or effects that were not measured or reported.

16. Why This Trial Matters Statistically

This study is statistically informative because it places a work-performance measure at the center of a randomized comparison among a support group, Cognitive Behavior Therapy, and Cognitive Behavior Therapy combined with Cognitive Remediation. Its primary measure is continuous, so the posted means and mean differences express results on the scale itself rather than reducing the outcome to a binary category.

The results also illustrate why point estimates, confidence intervals, and p-values should be read together. The mean differences describe the estimated size and direction of the group contrasts; the intervals convey uncertainty; and the unadjusted p-values describe compatibility with a null hypothesis under the comparison's assumptions. None of these quantities alone establishes practical importance. The registry record does not provide a threshold for meaningful change.

The sample-size illustrations show how planning depends on the effect a future study aims to detect: smaller assumed effects require more participants per arm under the stated planning assumptions. Those calculations use observed effects and are not a substitute for the trial's original design rationale, which is not reported in the registry record.

Finally, this record highlights the importance of transparent reporting. Details about masking, analysis populations, missing data, multiplicity, and the original statistical plan are needed to understand how posted estimates relate to the intended analysis. Their absence does not erase the reported results, but it narrows what can be concluded from them.

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 registry record leaves several trial-specific details unresolved. It reports randomized allocation and single masking but does not identify who was masked, describe the allocation process, or report concealment procedures. It does not provide intervention schedules, adherence information, or other details needed to understand how the behavioral interventions were implemented.

The overall enrollment entry is 87, while each arm's primary-outcome summary lists 25 participants. The registry record does not explain the relationship between those figures or state how many participants contributed to the analysis under any particular analysis population. Missing-data handling, reasons for unavailable outcomes, and sensitivity analyses are not reported.

The primary outcome is reported at six months, but the record does not give a threshold for a meaningful score difference or describe the score's interpretation beyond its scale range and direction. It does not report a direct comparison between Cognitive Behavior Therapy and the combined intervention. The reported comparisons instead contrast each with the support group.

The p-values are unadjusted, and multiplicity handling is not reported. The trial's original statistical plan, sample-size justification, and interim analyses are not reported in the registry record. These limitations constrain interpretation of the posted statistical evidence and make it inappropriate to infer unreported design or analysis decisions.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Cognitive Behavior Therapy and Work Outcome — NCT00810355.
• Registry record last updated 2017-05-23; status last verified 2017-04.
• Results first posted 2016-10-31.
• 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

The registry identifies NCT00810355, titled Cognitive Behavior Therapy and Work Outcome, with the official title Effects of CBT and Cognitive Remediation on Work in Schizophrenia. The listed sponsor is VA Office of Research and Development. The study is marked completed, randomized, single-masked, and parallel-group; phase is listed as NA.

The registry lists schizophrenia as the condition and enrollment as 87. The three arms are Support Group, Cognitive Behavior Therapy, and Cognitive Behavior Therapy and Cognitive Remediation. The primary outcome is Work Quality at six months, measured by the Work Behavior Inventory's total average of five subscales. Higher scores on its 1-5 scale represent better work performance.

The posted arm summaries list 25 participants per arm. The registry record does not report the original statistical plan, missing-data approach, analysis populations, or multiplicity procedure. The posted comparisons are unadjusted.