Biomarker Assessment of Glutamatergic Target Engagement: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Biomarker Assessment of Glutamatergic Target Engagement (NCT02134951), a randomized phase 4 study. The primary outcome is Glutamate + Glutamine (Glx) Response.

2. Clinical Question

The stated purpose was to assess the relative feasibility of two potential functional measures of target engagement—Glx MRS and BOLD fMRI—for systematic assessment of mGluR 2/3 in drug development for psychotic spectrum disorders. The posted primary result concerns Glx; the registry record does not include a posted analysis result for BOLD fMRI.

This is a biomarker-measurement question in healthy controls, not a clinical-outcome question in people with psychotic spectrum disorders. The response is defined through post-pre changes in the Glx over creatinine ratio, with higher values representing higher ratios. The record does not state a clinically meaningful threshold for this measure, nor does it report how a change in the ratio should be interpreted for symptoms or patient outcomes.

3. Trial Design

The registry identifies this as a Phase 4, randomized, triple-masked, parallel study, with an enrollment of 65. The listed condition is Healthy Controls. The sponsor is New York State Psychiatric Institute. The study began in 2014-05, had primary completion in 2015-10, and is marked completed.

The parallel design compares participants assigned to ketamine with participants assigned to placebo. The placebo was normal saline. The ketamine regimen is recorded as an intravenous bolus of 0.23mg/kg over 1 minutes, then 0.58 mg/kg/hr over 30 minutes, followed by 0.29mg/kg/hr over 64 minutes. The registry identifies masking as triple but does not specify which roles were masked or how masking was maintained.

The primary outcome is a continuous measure: the mean post-pre change in Glx over creatinine, assessed on Day 1. The outcome description identifies the measurement method as proton magnetic resonance spectroscopy (¹H MRS) and focuses on the first 15 minutes after ketamine. The posted result includes 31 participants in the ketamine arm and 16 in the placebo arm for this measure. These outcome counts differ from the registry’s enrollment figure; the record does not explain the relationship between them.

The registry lists two outcome measures and no analysis entries. It does not report the original sample-size justification, the planned statistical model, allocation ratio, planned analysis populations, or whether interim analyses were conducted. Those details should not be inferred from the posted outcome summaries or from the planning illustrations.

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.

Before assignment: 65 subjects were randomized, with results (Number started) reported for the 59 subjects randomized subjects with at least one valid scan

Overall Study

Analysis population for the primary outcome, as defined in the registry: Glx response in 1st 15 minutes post ketamine

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 Glutamate + Glutamine (Glx) Response, measured over Day 1.

The primary endpoint is the Glx response, expressed as the post-pre change in the Glx over creatinine ratio. Glx refers to glutamate plus glutamine in the outcome title. The record identifies ¹H MRS as the measurement method and says that higher values indicate higher Glx/creatinine ratios. The timeframe is Day 1, with the primary population description specifying the response in the first 15 minutes after ketamine.

Comparing change from before to after infusion is intended to focus the measurement on how the ratio changes around the infusion rather than on a post-infusion value alone. The registry does not give further detail about measurement timing, processing, or how repeated measurements were combined, so those aspects cannot be reconstructed from the outcome description.

The stated rationale is to assess the feasibility of functional measures of target engagement in drug development. A biomarker response is not itself a clinical outcome. The registry does not define a threshold for a meaningful change, establish how the Glx measure relates to clinical benefit, or report a posted primary result for the other named measure, BOLD fMRI. Accordingly, the endpoint supports interpretation of the measured Glx ratio response only.

7. Results Posted in the Registry

• Ketamine: mean 0.01 versus 0.01 on control; difference 0.01 (95% CI 0.00 to 0.02), standardized effect d = 0.70; z-test p = 0.027.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary measure is continuous, and the registry reports group means with standard errors. A mean describes the average recorded change in each arm. A standard error describes the estimated uncertainty of a mean; it is not a measure of the spread of individual participants’ measurements. The reported mean and standard error are 0.015 and 0.002 for ketamine, and 0.007 and 0.003 for placebo.

What does the mean difference describe?

The posted comparison is a mean difference of 0.008, calculated as the ketamine mean minus the placebo mean in the registry’s comparison record. A positive difference means the recorded mean change was higher in the ketamine arm. The difference is expressed on the Glx over creatinine ratio scale. It is an unadjusted comparison in the sense that the registry presents a direct difference between the group summaries; no adjustment variables or adjusted model are described.

The difference is a summary of the groups, not a statement that every participant had a higher response. Group means do not show the distribution of individual responses, and the registry does not post participant-level data. The reported standard errors give information about uncertainty in the arm means, but they do not disclose the full distribution or the degree of overlap between individuals’ measurements.

How should a confidence interval be read?

A confidence interval expresses uncertainty around an estimate under the method used to construct it. In general, a narrower interval indicates greater precision than a wider interval on the same scale. The interval reported for this comparison is 0.001 to 0.015. The registry record does not report the confidence level or the method used to calculate it, so those details should not be assumed.

The interval is for the between-arm mean difference, not for either arm’s mean separately. It gives a range of values compatible with the analysis procedure and observed data, under that procedure’s assumptions. It is not a guarantee that the true value lies within the endpoints, and it does not identify which values would matter biologically or clinically. No interpretation threshold is reported.

What does the p-value add?

The posted unadjusted p-value is 0.027. In general, a p-value describes the probability, under a specified null hypothesis and statistical model, of obtaining results at least as incompatible with that null as the observed result. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of the response.

The registry does not identify the statistical test, its assumptions, or the analysis plan. It also does not state whether this p-value was adjusted for any other comparisons. It should therefore be interpreted as the unadjusted value recorded for this comparison, not as evidence that all possible sources of uncertainty or multiplicity have been addressed.

Why can over-dispersion matter?

Over-dispersion occurs when variability in the data is greater than a model assumes. In general, a model that understates variability can produce uncertainty estimates that are too small. This issue is especially relevant to count outcomes or other settings where model assumptions about variability are important. The primary outcome in this record is a continuous ratio change, and the registry does not report a model or evidence of over-dispersion. It is therefore not possible to determine whether this issue was assessed or relevant to the analysis used.

The posted summaries do not provide the participant-level distribution needed to assess skew, outliers, or other features of the continuous data. The record also does not report missing-data handling, covariate adjustment, or sensitivity analyses. These omissions limit independent assessment of the analysis, even though the headline mean difference and its uncertainty are reported.

What can randomization and masking support?

Random assignment is intended, in general, to support a fair comparison by allocating participants to study groups without choosing assignments based on their outcomes. Masking is intended to reduce the influence of knowledge about assignment on study conduct or measurement. The registry labels the study randomized and triple masked, but does not describe the randomization procedure, concealment, masked roles, or success of masking. The design labels alone cannot answer those operational questions.

The posted comparison should be read as a summary of the measured Glx response in the two recorded arms. Randomization and masking are features of the registered design; they do not replace information about the analysis, outcome completeness, or measurement procedures. Those details are not reported in the registry record.

10. Confidence Intervals and Precision

The estimated mean difference is 0.008 in the Glx over creatinine ratio change, with a reported confidence interval from 0.001 to 0.015. The interval gives a sense of uncertainty around the difference: it spans values near zero through larger positive values. The record does not define a threshold that would distinguish a small from a meaningful biomarker response, so the interval cannot be classified in those terms.

The confidence level and interval-construction method are not reported in the registry record. Without those details, the interval can be described using its posted endpoints but not fully evaluated against a specific inferential procedure. Its interpretation also depends on the assumptions and analysis population used, which are not described.

The arm-level standard errors are 0.002 for ketamine and 0.003 for placebo. They indicate uncertainty in the estimated arm means, not participant-to-participant variability. The recorded outcome counts are 31 and 16, respectively. The registry does not explain why these counts differ or whether any outcome measurements were missing.

Precision is distinct from importance. A confidence interval quantifies uncertainty on the measured scale; it does not establish the biological relevance of Glx changes, measurement feasibility, or implications for clinical outcomes. Those interpretations require context and thresholds that are not reported.

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 figures are planning illustrations based on fractions of the observed effect, not the original trial’s design calculation. The assumptions listed for these illustrations are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. For each row, the effect to detect is the stated fraction of the observed effect. The figures are participants per arm, not a total across arms or a total number of events.

The 80% power column gives the illustrative number of participants per arm for a design intended to have an 80% chance of detecting the selected effect under the listed assumptions, if that effect and the assumptions are correct. The 90% power column gives the corresponding illustration for a 90% chance. These are planning concepts, not guarantees about a future study’s results.

The rows consider planning for 100%, 75%, and 50% of the observed effect. The figures increase as the effect used for planning becomes smaller: detecting a smaller difference generally requires more participants, all else equal. For example, the registry’s illustrations give 33 participants per arm for 80% power and 43 for 90% power when planning for 100% of the observed effect; for 50% of the observed effect, the corresponding figures are 129 and 172.

These values are not observed power. They are hypothetical planning calculations using the observed estimate as a reference, and the registry does not report the trial’s own original sample-size assumptions or justification. The curve should be read in the same planning context, not as evidence about the probability that the completed study detected an effect.

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 = 0.008; pooled standard deviation σ = 0.011.
2. n = 2 × (1.96 + 0.842)² × 0.011² / 0.008² = 32.0, rounded up to 33 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 <- 0.008                      # observed difference in means
sigma <- 0.0114309521329882                     # 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(2134951)
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 = 33 (80% power), 43 (90% power)
 75% of observed effect: n per arm = 57 (80% power), 77 (90% power)
 50% of observed effect: n per arm = 129 (80% power), 172 (90% power)
power.t.test: 33 
Simulated power at n = 33 per arm: 0.798 (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 two outcome measures and no analysis entries. It does not identify a multiplicity strategy, such as which outcomes were designated primary for inferential testing or whether any adjustment was planned. The posted p-value is unadjusted. Without the analysis plan, it is not possible to determine how the reported comparison relates to other outcomes or analyses that may have been considered.

The record describes the primary outcome and posts its group summaries and comparison. It does not report the analysis population definition, exclusions, protocol deviations, or whether all randomized participants were included. The outcome counts are 31 for ketamine and 16 for placebo, while the enrollment figure is 65. The registry does not explain the difference, and it should not be attributed to a particular reason.

Missing-data methods are not reported in the registry record. There is no description of how incomplete measurements were handled, whether any data were imputed, or whether sensitivity analyses addressed missingness. The record also does not state whether the analysis followed an intention-to-treat principle or another population definition.

These absences do not establish that no multiplicity, missing-data, or population decisions were made. They mean that the posted record does not document those decisions, limiting independent assessment of how they may affect the interpretation of the reported comparison.

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 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists serious adverse events for 39 participants at risk in the ketamine group and 20 at risk in the placebo group. It records zero serious adverse events affecting participants in each group. It also records zero deaths in each group. No serious adverse event terms are listed.

For other adverse events, the record lists six affected participants in the ketamine group and zero in the placebo group, with 39 and 20 at risk, respectively. These are the registry’s reported counts; they are not percentages, and no percentage calculation is added. The record does not provide event descriptions or further detail about severity, timing, or attribution.

Adverse-event counts are descriptive. They do not, by themselves, establish that an event was caused by an intervention or that no events occurred beyond those recorded. Definitions, ascertainment procedures, follow-up completeness, and any comparison method are not reported in the registry record. The absence of listed serious events should therefore be read as the posted count, not as a complete characterization of safety.

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

The posted result describes a higher mean Glx over creatinine change in the ketamine arm than in the placebo arm: 0.015 compared with 0.007. The reported difference is 0.008, with a confidence interval from 0.001 to 0.015 and an unadjusted p-value of 0.027. This is evidence about the recorded biomarker response under the study’s measurement conditions.

The result does not establish that the measured difference is clinically meaningful. The registry reports no threshold for meaningful Glx change and no link between the ratio response and symptoms, functioning, or other patient outcomes. The study population is listed as healthy controls, so the result should not be treated as a direct estimate for people with psychotic spectrum disorders.

The stated study purpose involved comparing the relative feasibility of Glx MRS and BOLD fMRI as functional measures of target engagement. The posted primary result is for Glx MRS. The registry record does not include a corresponding posted BOLD fMRI result or a direct comparison of feasibility measures, so the posted Glx result alone cannot resolve that broader objective.

The randomized, triple-masked, parallel labels describe features of the registered design. The record does not report enough detail about the randomization process, masking roles, analysis plan, missing data, or outcome measurement procedures to assess those aspects fully. It also does not provide a stated threshold for target engagement.

Accordingly, the result is best understood as a group-level difference in a continuous biomarker measure, with uncertainty recorded by the interval and p-value. It does not establish treatment benefit, clinical efficacy, or a clinical recommendation.

16. Why This Trial Matters Statistically

This trial is statistically interesting because it focuses on a measurement question rather than a clinical outcome. The stated aim was to assess the relative feasibility of Glx MRS and BOLD fMRI for evaluating target engagement. That distinction matters: a biomarker can be studied as a measurement or pharmacodynamic signal without being a validated surrogate for clinical benefit.

The primary outcome is a continuous change in Glx over creatinine, and the record reports means, standard errors, a mean difference, a confidence interval, and an unadjusted p-value. Together, these summaries allow readers to consider both the direction of the group contrast and the uncertainty around it. They do not show the individual response distribution or establish a threshold for a meaningful change.

The record also illustrates why results need their analysis context. The trial is described as randomized and triple masked, but procedural details, analysis populations, missing-data handling, and multiplicity plans are not reported. The difference between the enrollment figure and the posted outcome counts is unexplained. These gaps do not erase the reported estimate, but they constrain assessment of how it was obtained and how broadly it can be interpreted.

Finally, the planning illustrations translate the observed estimate into hypothetical sample-size scenarios under stated assumptions. They may help frame future study planning, but they are not the original design justification and do not describe the power of the completed study. Keeping estimation, uncertainty, feasibility, and clinical interpretation separate is central to reading this biomarker result responsibly.

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 does not describe eligibility criteria beyond listing Healthy Controls, participant characteristics, or the recruitment process. Generalizability to other populations is therefore uncertain. In particular, the study purpose refers to drug development for psychotic spectrum disorders, but the listed study population is healthy controls.

The primary outcome description identifies the measure, scale, timeframe, and broad post-pre calculation, but does not detail acquisition procedures, the exact timing of measurements, processing choices, or quality-control rules. The record does not state how Glx MRS feasibility was defined or report the BOLD fMRI result needed to assess the stated comparison between potential measures.

The outcome summaries include 31 participants in the ketamine arm and 16 in the placebo arm, while the registry lists enrollment of 65. The reason for these different counts is not reported. The record also does not describe missing measurements, exclusions, analysis populations, or sensitivity analyses.

Although the study is labeled randomized and triple masked, the registry does not describe the allocation procedure, concealment, which roles were masked, or whether masking was maintained. The statistical test, model, confidence level, and interval method are not reported. Nor are the original sample-size justification, multiplicity plan, or interim analyses.

These limitations restrict independent evaluation of the primary estimate and its scope. They do not change the values posted in the record, but they leave important methodological context unavailable.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Biomarker Assessment of Glutamatergic Target Engagement — NCT02134951.
• Registry record last updated 2018-08-17; status last verified 2018-08.
• Results first posted 2018-02-13.
• 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

NCT02134951, Biomarker Assessment of Glutamatergic Target Engagement, is listed as a completed Phase 4 randomized, triple-masked, parallel study sponsored by New York State Psychiatric Institute. The registry lists Healthy Controls, enrollment of 65, a start date of 2014-05, and primary completion in 2015-10.

The primary outcome is the Day 1 Glx response measured by ¹H MRS as post-pre change in the Glx over creatinine ratio. The posted mean changes are 0.015 for ketamine and 0.007 for placebo; the reported mean difference is 0.008, with a confidence interval from 0.001 to 0.015 and an unadjusted p-value of 0.027.

The record lists two outcome measures and no analysis entries. It does not report the original sample-size justification, detailed statistical plan, missing-data approach, or analysis populations. Safety listings record zero serious adverse events and zero deaths in both groups, alongside six other adverse-event-affected participants in the ketamine group and none in the placebo group.