The Effects of Manipulating Expectations in a Gratitude Intervention: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effects of Manipulating Expectations in a Gratitude Intervention (NCT03784001), a randomized na study. The primary outcome is Mental Health Continuum-Short Form (MHC-SF).

2. Clinical Question

The key conceptual comparison is between gratitude with expectations and gratitude without expectations: both arms involve gratitude lists, while the additional benefit information distinguishes them. The events-control arm offers a different writing activity for context. The registry record identifies the trial as randomized, but does not report details of the randomization procedure or the intended primary statistical contrast. It therefore does not establish whether the primary question was framed as a comparison between the two gratitude arms, comparisons involving the control arm, or an overall test across all arms.

3. Trial Design

The registry describes a randomized, single-masked, parallel-group study with three behavioral intervention conditions: Gratitude + No Expectations, Gratitude + Expectations, and Events Control. Enrollment was 125. The study is marked completed, with a start date of 2019-02-05 and a primary completion date of 2019-02-28. The phase is listed as NA, and the sponsor is the University of California, Los Angeles.

The two gratitude arms used online lists of up to five items participants were grateful for every two days for two weeks. The expectations arm also included information about a benefit of gratitude each time a list was written. The control arm used online lists of up to five events from the participant’s day every two days for two weeks. These descriptions define the activities, but do not specify adherence requirements, how completion was monitored, or what happened when a participant missed an activity; such details are not reported in the registry record.

Single masking is recorded, but the identity of the masked party and the procedures used to maintain masking are not reported in the registry record. Random allocation is stated, but its method, allocation ratio, and any stratification or blocking procedures are not reported in the registry record. Although enrollment is recorded, the number assigned to each arm, the number completing follow-up, and the number included in each analysis are not reported in the registry record.

The primary outcome was assessed at pre-intervention and post-intervention, described as two weeks apart. The registry also lists secondary measures concerning sleep disturbance, sleep duration, positive emotions, perceived stress, depression, and state gratitude. It lists nine outcome measures overall. The timing and analysis details for each secondary measure are not reported in the registry record. The design supports a question about the added role of expectations, but the posted record does not give the analytical details needed to identify the exact planned contrast or model.

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

Analysis population for the primary outcome, as defined in the registry: These are the numbers analyzed when assessing overall well-being

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 Mental Health Continuum-Short Form (MHC-SF), measured over Assessed at Pre- and Post- Intervention (2 weeks apart).

The primary endpoint is the Mental Health Continuum-Short Form (MHC-SF), a self-report measure intended to assess hedonic well-being, eudaimonic well-being, and overall well-being. Participants rate how often they experience 14 emotions or statements, including happiness and satisfaction with life. Responses use a 6-point Likert scale, from 0 = never to 5 = everyday. The total score is the sum of item scores, with a range of 0-70; higher scores indicate greater overall well-being.

Using a defined measure gives investigators a consistent way to summarize participants’ reported well-being rather than relying on an informal impression. Assessing it before and after the intervention can describe change over the intervention period, while comparisons among randomized arms can address whether the pattern differs by activity or by the added expectations information. Those are general purposes of repeated measurement and randomized comparisons; they do not establish that a particular analysis was carried out in this study.

The registry describes the MHC-SF as reliable and valid for use with young adults. That rationale is relevant to a study whose intended participants were undergraduate college students. The endpoint remains a self-reported score, so it represents participants’ responses to the measure rather than an independently observed clinical event. The registry record gives the endpoint definition and assessment timing, but does not report arm-level scores, changes, effect estimates, confidence intervals, or a statistical test for the primary outcome. Thus, the endpoint is clearly described, while its observed results are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies randomization, a parallel-group structure, and three intervention conditions. It does not report the statistical analysis plan or the inferential results. The explanations below describe general statistical ideas relevant to this design; they should not be read as a description of methods confirmed to have been used in the trial.

What does randomization contribute?

In general, random assignment is intended to make the intervention groups comparable, on average, before the activities begin. It can reduce systematic differences in baseline characteristics as an explanation for later differences in outcomes. It does not guarantee that groups are identical, particularly in a study of limited size, and it does not remove the need to report baseline information, follow-up, and the analysis population. The registry states that the study was randomized but does not report the allocation method, group counts, or a baseline comparison.

How should pre- and post-intervention scores be understood?

The MHC-SF was assessed at pre-intervention and post-intervention, two weeks apart. In general, a within-person change describes how scores differ across assessments for the same participant. A between-group comparison asks whether those changes, or the post-intervention scores after accounting for baseline, differ across assigned conditions. Those questions are not interchangeable. A change within one arm alone does not establish that its intervention produced a different outcome from another arm. The registry record does not specify which approach was planned or report an estimate from either approach.

What do means and standard deviations describe?

The primary outcome is characterized as a continuous score summarized by a mean and standard deviation. In general, a mean describes the central value of a group’s scores, while a standard deviation describes how spread out individual scores are around that mean. Neither alone describes the uncertainty in a comparison between arms. An estimated difference accompanied by a confidence interval would communicate both the estimated contrast and the range of values compatible with the data under the model. No group means, standard deviations, contrasts, or confidence intervals for the primary outcome are reported in the registry record.

Why does the contrast need to be stated?

With three arms, there are multiple possible comparisons. The question about expectations most directly concerns gratitude with expectations versus gratitude without expectations. Comparisons of either gratitude arm with events control address different questions about the writing activities. An overall test across all arms would test whether any group-level difference is present, without by itself identifying which pair of arms differs. In general, a clear analysis plan should name the primary contrast and explain how other contrasts will be interpreted. The registry record does not report the planned contrast, model, or test.

What can a p-value or confidence interval tell a reader?

In general, a p-value summarizes how incompatible the observed data are with a specified null model, under the assumptions of the analysis. It does not measure the probability that the null hypothesis is true, and it does not quantify the size or practical importance of a difference. A confidence interval conveys uncertainty around an estimate and helps readers assess which effect sizes remain compatible with the data and analysis assumptions. These measures are most useful alongside the estimated effect and the number of participants analyzed. None of these primary-result statistics is reported in the registry record.

How should planning calculations be interpreted?

In general, sample-size calculations are planning tools: they describe the participant count needed under stated assumptions to detect a chosen effect with a chosen statistical procedure. The record describes planning illustrations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is stated as a fraction of the observed effect. These are planning assumptions, not a report of the trial’s original design justification. The registry record does not report the trial’s own sample-size justification. Planning illustrations must not be read as observed power or as evidence that an effect was found. In the absence of the primary outcome results and specific illustration values in the registry record, their numerical implications cannot be assessed.

Over-dispersion is a general issue for outcomes whose variability exceeds what a chosen model expects; if present and ignored, uncertainty estimates can be too small. The MHC-SF is a bounded summed score, but the registry record does not report a distributional assessment or a model, so it is not possible to determine whether over-dispersion was relevant or how it was handled. More broadly, the suitability of any model depends on the observed data, the estimand, and the assumptions used; these details are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The study lists the MHC-SF as the primary outcome and lists secondary measures covering sleep disturbance, sleep duration, positive emotions, perceived stress, depression, and state gratitude. The registry states that there are nine outcome measures overall. Considering several outcomes or several comparisons raises a general multiplicity issue: if many statistical tests are conducted, the chance of at least one apparently unusual result can increase. Researchers may address this through a prespecified outcome hierarchy, adjusted testing, or cautious interpretation. The registry record does not report whether any of these approaches was planned or used.

Missing-data handling is also important for a pre- and post-intervention outcome. Participants may not complete every assessment, and the analyzed set can differ from those enrolled or randomized. General analysis approaches make different assumptions about missing outcomes; those assumptions affect how estimates should be interpreted. The registry record does not report missing-data methods, completion counts, reasons for missingness, or group-specific numbers analyzed. It therefore does not establish whether the primary analysis included all randomized participants or a subset.

The record gives total enrollment but no participant flow by arm, and it does not report the statistical analysis population. Details such as intention-to-treat handling, exclusion criteria, protocol deviations, and treatment of incomplete questionnaires are not reported in the registry record. These omissions prevent assessment of whether the analyzed population preserved the benefits of randomization or whether missingness could have influenced the reported estimates. No primary or secondary analyses are reported in the registry record, so the effects of any multiplicity or missing-data decisions cannot be evaluated.

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

The study’s stated purpose is to test whether setting expectations about gratitude’s benefits changes outcomes from a brief gratitude intervention. Its three-arm design distinguishes gratitude lists accompanied by benefit information, gratitude lists without that information, and a daily-events writing activity. The primary outcome is a self-reported overall well-being score measured before and after the intervention.

These design features describe what the study was designed to ask; they do not, by themselves, show what happened to participants’ scores. The registry record does not report primary outcome estimates, uncertainty intervals, or statistical tests. It is therefore not possible to say whether one arm had higher or lower well-being scores, whether the arms changed differently over time, or how precise any comparison was. Nor does missing results mean that the intervention had no effect.

Even if an arm-level difference were reported, statistical interpretation would depend on the size and uncertainty of that estimate, the selected comparison, the analysis population, and the assumptions of the analysis. A statistical difference would not automatically establish practical importance, while a result that is not statistically distinguishable from no difference would not prove the groups are identical. These are general interpretive principles; the registry record contains no estimate to which they can be applied.

The enrollment figure of 125 describes the trial record, not necessarily the number contributing data to the primary analysis. The listed zero adverse-event counts, together with zero participants at risk in those fields, also do not establish an absence of adverse events. The record does not provide the context needed to interpret those entries as a complete safety assessment.

Accordingly, the defensible conclusion is limited: the registry describes a randomized study of expectations within a gratitude intervention, but does not report outcome results sufficient to determine the observed well-being pattern or its statistical precision.

12. Why This Trial Matters Statistically

This study raises a useful design question: when two groups undertake the same gratitude-list activity, does adding information about gratitude’s benefits change the measured outcome? Including a gratitude arm without expectations and an events-control arm separates the expectations question from the broader question of how gratitude-list activity compares with another writing task. That structure makes the intended comparisons important to define in advance.

The trial also illustrates why outcome reporting is essential to statistical interpretation. A design description and a named endpoint tell readers what investigators intended to study, but they cannot establish an effect. Without arm-specific results, an analysis contrast, and an account of uncertainty, a reader cannot distinguish a substantial difference from a small or imprecisely estimated one. Enrollment alone is not a substitute for the number analyzed or the outcome data.

Multiple listed outcomes make transparent prioritization especially relevant. A prespecified primary comparison and clear treatment of secondary outcomes help readers understand which findings answer the central question and how to interpret exploratory results. The registry record does not report the analysis plan or outcome analyses, leaving those statistical considerations unresolved.

Finally, the study highlights a general distinction between a planning calculation and evidence from observed data. Sample-size illustrations under assumptions can inform design, but they are not a measure of the strength of a completed trial’s findings. Interpreting a completed randomized study requires the observed effect estimates and their uncertainty, neither of which is reported for the primary endpoint in the registry record.

13. 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 most consequential limitation for interpreting this trial is that the registry record does not report primary outcome results. There are no arm-level MHC-SF summaries, between-arm estimates, confidence intervals, or p-values available in the record. The trial’s stated question can therefore be described, but its observed answer cannot be evaluated statistically.

Enrollment is reported as 125, but the record does not give the numbers assigned to each arm or analyzed at pre- and post-intervention. Without participant flow, it is not possible to assess completion, attrition, or how the analysis population relates to those enrolled. The record also does not report missing-data procedures, adherence to the online activities, or whether incomplete activity records affected inclusion in an analysis.

The randomized design is identified, but details of sequence generation, allocation concealment, and the party masked are not reported in the registry record. The exact primary comparison and statistical model are also not reported. These gaps make it difficult to assess whether the analysis, if conducted, directly addressed the expectations question or how it handled the three-arm structure and repeated outcome measurement.

The registry lists multiple secondary measures and nine outcome measures overall, but does not describe a multiplicity strategy or provide secondary results. This limits assessment of whether outcome selection and statistical testing were prespecified and how any secondary findings should be interpreted. The adverse-event fields list zero counts and zero participants at risk, which does not allow a complete assessment of adverse-event ascertainment or frequency. These limitations concern the information available in the registry record; they do not establish that the corresponding procedures or data were absent from the study itself.

14. Related Tutorials

15. Related Statistical Calculators

16. Sources

• ClinicalTrials.gov: The Effects of Manipulating Expectations in a Gratitude Intervention — NCT03784001.
• Registry record last updated 2020-06-09; status last verified 2020-05.
• Results first posted 2020-06-09.
• 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.

17. Record Summary

NCT03784001, titled The Effects of Manipulating Expectations in a Gratitude Intervention, is recorded as a completed, randomized, single-masked, parallel-group behavioral study sponsored by the University of California, Los Angeles. Enrollment was 125. The study began on 2019-02-05 and had a primary completion date of 2019-02-28.

The three conditions were Gratitude + No Expectations, Gratitude + Expectations, and Events Control. The primary measure was the MHC-SF, assessed at pre-intervention and post-intervention, two weeks apart. The registry also lists secondary sleep, emotion, stress, depression, and gratitude measures.

Primary and secondary outcome analyses are not reported in the registry record. Group-specific analyzed counts, missing-data methods, multiplicity procedures, and the statistical analysis plan are also not reported. The available record describes the study design and outcome definitions, but does not provide the results needed to estimate or interpret intervention effects.