A Psychological-behavioral Intervention to Increase Activity in Type 2 Diabetes: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Psychological-behavioral Intervention to Increase Activity in Type 2 Diabetes (NCT03164538), a randomized na study. The primary outcome is Number of PP-MI Sessions Completed by Participants.

2. Clinical Question

3. Trial Design

The registry describes a randomized, single-masked, parallel-group trial of PP-MI and diabetes education. The study enrolled 70 participants and is marked completed. The recorded start date is 2017-07-25, and the primary completion date is 2019-10-10. Massachusetts General Hospital is listed as the sponsor. The phase is recorded as not applicable.

The intervention was behavioral. In the PP-MI group, participants were to work through positive psychology exercises, set physical activity goals, and discuss their work during weekly telephone calls with a study trainer. The trainer was to use motivational interviewing techniques while facilitating goal setting. The diabetes education group also received weekly telephone calls, with education about health behaviors relevant to diabetes. The descriptions identify physical activity, medication adherence, and diet as possible topics for those calls.

Random assignment supports a planned comparison between the groups, but the registry record does not state the allocation ratio or identify who was masked. It also does not report further details about sequence generation, concealment of assignment, or the handling of departures from assigned intervention. Those features should not be inferred from the general design labels.

The study summary identifies feasibility, acceptability, and potential impact as areas of interest. The primary registry outcome, however, is session completion in the PP-MI group, while listed secondary outcomes include ratings of ease and utility, changes in physical activity and sedentary time, and change in positive affect. Numerical outcome results and a reported between-group estimate are not included in the registry information available for interpretation.

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 Number of PP-MI Sessions Completed by Participants, measured over 16 weeks.

The primary endpoint is the number of PP-MI sessions completed by participants assigned to PP-MI during 16 weeks. It is described as a mean with standard deviation and is measured in sessions completed. It applies to the PP-MI group, not to both groups as a direct comparative endpoint.

Session completion is relevant to feasibility because it records whether participants took part in the intervention activities. It can help describe engagement with the intervention as delivered, but it does not by itself establish whether participants changed their physical activity or whether any change was attributable to PP-MI. Nor does session completion alone establish acceptability; the registry lists separate ease and utility outcomes for the intervention components.

The registry record does not report the observed mean number of sessions completed, its standard deviation, or a confidence interval. Without those results, the degree of participation and the precision of its estimate cannot be evaluated. The measure’s definition also does not specify, in the information recorded, how a partially completed session was handled or how missing session records were treated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry labels the study randomized and parallel-group. Randomization is a design method intended to make assigned groups comparable, on average, with respect to both measured and unmeasured characteristics. It does not guarantee identical groups in a particular trial. The parallel structure means the groups were assigned to different intervention approaches rather than being described as sequential treatment periods. The record does not give enough detail to assess the randomization procedure or identify the masked party.

What does the primary measure estimate?

The primary outcome is a continuous measure summarized by a mean and standard deviation. The mean describes the average number of sessions completed within the PP-MI group. The standard deviation describes variability among the individual session-completion values; it is not the uncertainty around the mean. A confidence interval for the mean, if reported, would address the precision of the estimated average. Neither the mean nor the standard deviation is reported in the registry record, and no confidence interval is given.

Because the endpoint is defined for the PP-MI group alone, it does not directly estimate a difference between the randomized groups. A separate comparative endpoint would be needed to estimate a between-group contrast. The listed secondary outcomes include changes in physical activity, sedentary time, and positive affect, but their numerical results and analysis details are not reported in the registry record.

How should an uncertainty interval be read?

In general, a confidence interval expresses the precision of an estimate under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval, but interpretation also depends on the outcome scale, the estimate, and the interval’s compatibility with values of substantive interest. A confidence interval is not a guarantee that the true effect lies within its limits. No interval for the primary endpoint or a group contrast is reported in the registry record.

What does the planning illustration mean?

The planning assumptions recorded for sample-size illustrations use a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation. The effect to detect is expressed as a stated fraction of the observed effect. These are assumptions for planning illustrations, not a description of the trial’s original design justification. The registry record does not report the original sample-size justification or identify an effect size used to plan this trial.

In general, a planning calculation estimates the sample size that would be needed under specified assumptions. It is not a measure of the probability that the completed trial detected an effect. Such calculations depend on the assumed effect, outcome variability, analysis method, and other design choices. Any planning illustration based on an observed effect should be read as conditional on that effect estimate and its assumptions, not as observed power. Numerical planning results are not reported in the registry record used for this interpretation.

Why can variability affect analysis?

For a continuous outcome, the standard deviation describes the spread of individual observations. If the observations are more variable, an estimate of a group average or group difference will generally be less precise, all else being equal. This general principle does not establish the variability in this trial: the primary outcome’s standard deviation is not reported.

Over-dispersion is a general concern when count data vary more than a chosen statistical model expects. It can make standard errors too small if the model does not account for the extra variability. The primary measure is a count of sessions, but the registry does not report its distribution or the model used to analyze it. There is therefore no basis to conclude that over-dispersion occurred or to identify a particular count model as the trial’s analysis.

What is missing from the analysis description?

The record does not report an analysis method for the primary endpoint, a prespecified contrast, adjustments for baseline values, or a plan for handling missing observations. It also does not identify an analysis population, such as whether all randomized participants were included regardless of intervention completion. These details matter because analytic choices can affect both the estimate and its uncertainty. They should not be filled in by assumption.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Positive Psychology + Motivational Interviewing")
n   <- c(35)
m   <- c(11)
sp  <- c(4.45)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Positive Psychology + Motivational Interviewing  35  11.000  4.450  9.471  12.529

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 25 outcome measures, including secondary outcomes concerning component ease and utility, physical activity, sedentary time, and positive affect. Examining several outcomes creates a general multiplicity issue: the chance of at least one apparently notable result can increase when many hypotheses are tested. This does not mean that any particular result is false, but it makes a prespecified hierarchy or multiplicity strategy useful for interpretation.

A multiplicity adjustment, outcome hierarchy, or other plan for interpreting multiple tests is not reported in the registry record. The record also lists zero analyses, so it does not provide the statistical results needed to evaluate how multiple outcomes were handled. No claim about adjustment or selective reporting can be made from the outcome list alone.

Missing-data methods are not reported in the registry record. The record does not describe how missing session records, missing questionnaire responses, or missing physical activity measurements were handled, or whether any sensitivity analyses were planned. Missingness can affect interpretation if the observations that are unavailable differ systematically from those that are observed; that is a general concern, not a documented feature of this trial.

The analysis population is also not reported. Although the trial is described as randomized, the record does not say whether analyses were based on assigned groups, participants who completed intervention activities, or another population. These distinctions can affect the meaning of an estimate, particularly when participation is itself an outcome of interest. No analysis population or missing-data approach should be inferred.

12. 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

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: unexpected atrial fibrillation (5.7%), leg infection (2.9%), unexpected acute respiratory failure (2.9%).

The registry’s serious-event fields list 35 at risk in each group. The serious-event value is 4 for PP-MI and 0 for diabetes education; deaths are recorded as 0 in both groups. The other-adverse-event values are 12 for PP-MI and 6 for diabetes education. These are registry entries, not estimates adjusted for follow-up, exposure, or differences in participant characteristics.

The listed serious-event terms are Unexpected Atrial Fibrillation (5.7%), Leg infection (2.9%), and Unexpected acute respiratory failure (2.9%). The registry information does not assign these terms to a specific group, so they should not be attributed to either intervention on the basis of the available record. Nor does the listing establish that an event was caused by an intervention.

Adverse-event counts describe reported safety events within the registry’s recording framework. Interpreting them requires context such as event definitions, ascertainment procedures, timing, severity, and attribution. Further details on these points are not reported in the registry record. The figures therefore describe the recorded entries but do not, by themselves, establish a comparative safety effect.

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

The record describes a completed randomized trial of a behavioral intervention combining positive psychology exercises with motivational interviewing, compared with telephone diabetes education. It identifies session completion in the PP-MI group as the primary outcome and lists additional outcomes relevant to feasibility, acceptability, physical activity, sedentary time, and positive affect. This information clarifies the study’s aims and the measures it intended to assess.

The record does not report the primary outcome’s mean or standard deviation, nor does it provide a comparative estimate or uncertainty interval for the secondary outcomes. As a result, the posted registry information does not quantify intervention participation or show the size, direction, or precision of changes in the listed outcomes. The absence of numerical results in the registry record is not evidence that outcomes did not change.

Session completion can describe engagement with the PP-MI program, but it is not itself a measure of physical activity change or a comparison with diabetes education. Likewise, a randomized design is a way to support causal comparisons when outcomes and analyses are reported; the design label alone is not a result. The registry information does not support a conclusion that one approach was superior, equivalent, or ineffective.

The safety entries should also be interpreted as recorded event information rather than proof of causation or a complete comparative safety assessment. Additional details about event definitions and attribution are not reported in the registry record. Overall, the available record describes the intervention and planned outcome domains, but leaves the numerical efficacy, feasibility, and safety interpretation unresolved.

14. Why This Trial Matters Statistically

This trial illustrates why the endpoint’s definition matters. Session completion addresses participation in the PP-MI intervention, while physical activity outcomes address behavior change. Those are related questions but are not interchangeable. A study may define a meaningful feasibility measure without that measure establishing the effect of the intervention on a behavioral outcome.

The randomized parallel-group design indicates an intended comparison with diabetes education, and the registry describes telephone contact in both groups. That comparator context matters: the research question is not simply whether participants receive calls, but whether the intervention approaches differ on outcomes of interest. The registry’s primary endpoint, however, is defined within the PP-MI group and cannot by itself provide that between-group contrast.

The record also illustrates the distinction between trial registration details and an interpretable results report. The outcome names and design characteristics help readers understand what was planned, but numerical estimates, their uncertainty, and analysis choices are needed to assess what was observed. With 25 outcome measures listed and no analyses reported, it is especially important not to infer a pattern of results from the study’s aims or outcome list.

For biostatistical interpretation, the central issue is not whether a particular analysis can be imagined, but whether the registry record reports the information needed to evaluate it. Here, key primary outcome estimates, analysis methods, missing-data handling, and multiplicity plans are not reported in the registry record. Recognizing those gaps prevents a study description from being mistaken for evidence of a particular outcome.

15. 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 main limitation for interpreting this trial from the registry record is the absence of numerical outcome results. The primary measure is defined, but its mean and standard deviation are not reported. The listed secondary outcomes likewise have no numerical estimates in the record. This prevents evaluation of outcome magnitude, variability, and precision.

The primary endpoint is restricted to the PP-MI group, so it is not a direct comparison with diabetes education. The record does not report a comparative estimate for the listed physical activity or other secondary outcomes. It also does not describe the statistical methods used for the outcomes, an analysis population, or missing-data handling. Those omissions limit assessment of whether the analyses addressed the randomized assignment and how incomplete observations might affect conclusions.

Although the study is described as single-masked, the masked party is not reported in the registry record. Further details of randomization and allocation concealment are also not reported. The record does not provide eligibility criteria or enough information to judge how closely the enrolled participants represent a broader population of people with type 2 diabetes.

Safety interpretation is limited by the lack of reported detail on event definitions, ascertainment, timing, and attribution. The serious-event terms are not assigned to a particular group in the listed information. The registry record also does not report an original sample-size justification or a multiplicity plan. These are limitations of what can be concluded from the registry information, and do not establish that the corresponding methods or analyses were absent from all study documentation.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: A Psychological-behavioral Intervention to Increase Activity in Type 2 Diabetes — NCT03164538.
• Registry record last updated 2021-02-21; status last verified 2021-02.
• Results first posted 2021-02-21.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

NCT03164538 is a completed randomized, single-masked, parallel-group behavioral trial sponsored by Massachusetts General Hospital. The record concerns people with type 2 diabetes and describes a 16-week comparison of positive psychology plus motivational interviewing with diabetes education delivered by telephone. Enrollment is recorded as 70.

The primary outcome is the mean number of PP-MI sessions completed by participants in the PP-MI group, with standard deviation as the stated dispersion measure. The registry record does not report numerical results for this endpoint or comparative estimates for the listed secondary outcomes. It lists 25 outcome measures and zero analyses. Serious-event and other-adverse-event entries are recorded, but details needed for full comparative safety interpretation are not reported. The record therefore describes the trial design and outcome domains without furnishing the numerical results needed to judge the observed effects.