Investigation of the Effects of Bariatric Surgery on Taste Reward in Humans: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Investigation of the Effects of Bariatric Surgery on Taste Reward in Humans (NCT01531738), a registered phase not stated study. The primary outcome is Breakpoints as Assessed by Change in the Number of Mouse Clicks in the Last Completed Ratio.

2. Clinical Question

3. Trial Design

This is a completed clinical study sponsored by Imperial College London. The registry lists an enrollment of 22 and describes two groups: obese patients due to undergo gastric bypass or gastric banding, and normal-weight healthy volunteers. Allocation is not stated. The registry record therefore does not support treating the groups as randomized or as a like-for-like comparison.

The surgical patients were scheduled for assessment 2 weeks before surgery and again 8-12 weeks post operatively. The control volunteers were scheduled for assessment on two occasions 10-14 weeks apart. This allows the study to describe changes over time within each group, but the groups differ by weight status and by whether they undergo surgery. The record does not report the actual timing of each participant’s assessments, whether all scheduled assessments were completed, or how any differences between the groups were handled in analysis.

The primary outcome is a continuous measure: the breakpoint, expressed in clicks, in a task involving chocolate rewards. Hunger and Body Mass Index are listed as secondary outcomes. Although the study aim refers to sweet, fatty, and vegetable or fruit tastes, the registry record does not report analyses for those taste categories. It also does not report a statistical analysis plan, adjustment variables, a sample-size justification, or an analysis population. The status is COMPLETED, but completion status alone does not establish that every planned assessment or analysis was carried out.

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 Breakpoints as Assessed by Change in the Number of Mouse Clicks in the Last Completed Ratio, measured over 2 weeks pre and 8-12 weeks post operatively for surgical patients or on two occasions 10-14 weeks apart for normal weight control group.

The primary endpoint is the breakpoint in a computer-based effort task. Participants sat in front of a screen and a plate of 20 chocolate candies. They could click to earn a candy, consume it, and choose whether to continue to the next effort level. The first ratio required 10 clicks, with a geometric increment of 2 at each subsequent ratio. Participants could stop by pressing the spacebar when they no longer wished to continue. The breakpoint was the point at which the session ended; the registry names the endpoint as the number of mouse clicks in the last completed ratio.

This measure is intended to capture how much effort a participant will make to obtain a chocolate reward under the task conditions. A higher breakpoint would represent completion of a more demanding ratio in this task, not a direct measure of overall appetite, food intake, or preference across everyday settings. The registry specifies that the measure is summarized as a mean with standard deviation and uses clicks as the unit.

Repeated assessment makes the endpoint suitable for examining within-person change over time, including before and after surgery in the surgical group. However, the registry record reports no numerical breakpoint estimates, changes, confidence intervals, or statistical tests. The endpoint’s interpretation is therefore limited to what the task is designed to measure, rather than any claim about an observed change.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the primary outcome as a continuous measure summarized by a mean and standard deviation. The mean describes the average breakpoint in the group being analyzed; the standard deviation describes how spread out individual measurements are around that average. These summaries answer different questions: the mean describes a group’s central value, while the standard deviation describes variation among its participants. The registry record gives the intended summary format but does not report the actual means or standard deviations.

What does the breakpoint represent?

The task raises the effort required to earn another chocolate candy by increasing the click ratio geometrically. A participant who completes a ratio has reached that effort level for the reward available in the task. The breakpoint is the final completed ratio before the participant ends the session. As a general statistical concept, this is an operational measure: it gives a defined way to quantify behavior in a particular setting. It should not be treated as a direct measure of every aspect of taste, appetite, or food choice.

Because the measure is recorded in clicks, its interpretation depends on the task setup and how participants engage with it. The registry describes the reward, instructions, stopping procedure, and ratio progression, but does not report information about task standardization across sessions, assessor procedures, or participant familiarity with the computer task. Such details could matter when interpreting repeated measurements, but they are not reported in the registry record.

How should repeated measurements be understood?

The surgical group was scheduled for assessment before and after surgery, while controls were scheduled for two assessments separated by 10-14 weeks. In general, repeated measurements can help distinguish a person’s change over time from variation between different people. A paired analysis would account for the fact that measurements from the same person are related. However, the registry record does not specify whether a paired method was used, how the repeated assessments were modeled, or whether the main analysis compared changes between groups.

A before-after change in the surgical group alone cannot isolate the influence of surgery from other changes over the same period. A control group assessed at two occasions can provide context for temporal variation, but interpretation still depends on comparability of the groups and the analysis strategy. Here, the surgical patients and normal-weight healthy controls differ in the way they are described, and allocation is not stated. The record does not report a method for controlling confounding or a prespecified approach to baseline differences.

What would uncertainty estimates add?

As a general statistical concept, a confidence interval expresses the range of values reasonably compatible with an estimate under the analysis assumptions. A narrow interval indicates greater precision than a wide interval, while an interval that includes values on both sides of a null contrast can indicate uncertainty about the direction or size of a difference. A confidence interval does not guarantee that an estimate is unbiased or that the model assumptions are appropriate. No confidence interval is reported for the primary endpoint in the registry record, so its precision cannot be assessed.

A p-value, when reported, describes how unusual the data would be under a specified null model and its assumptions. It does not measure the probability that the null hypothesis is true, nor does it indicate whether an effect is important. The registry record reports no outcome p-values or statistical tests. A statistical conclusion should not be inferred from the study’s COMPLETED status or from the presence of a named endpoint.

Why can variation matter?

Standard deviations describe observed spread, but the record provides no values with which to assess that spread. As a general explanation, if participant responses vary considerably, an average can conceal meaningful differences in individual patterns and an estimate of a group contrast can be less precise. If the distribution of a continuous measure is markedly asymmetric or contains influential observations, a mean-based analysis may also require careful checking. The registry does not report distributions, diagnostic checks, transformations, or alternative summaries.

Over-dispersion is a concern for count outcomes when observed variability is greater than expected under a chosen count model. As a general concept, it can make model-based uncertainty estimates too small if not addressed. The primary endpoint is reported as a continuous mean in clicks, and the registry does not describe a count model or over-dispersion assessment. This general issue cannot be used to infer what analysis was performed.

What does the planning framework mean?

The sample-size planning description is explicitly an illustration based on the observed effect, not the trial’s own design justification. It specifies a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation, with the effect to detect expressed as a stated fraction of the observed effect. For non-time-to-event outcomes, planning quantities are described as participants per arm. These assumptions describe a planning calculation, not an observed result, and they do not establish that the trial was designed or powered using that calculation.

Any such planning illustration is not observed power and cannot substitute for the analysis estimate or its uncertainty. The registry record does not report a prospective sample-size justification or explain how an effect worth detecting was selected. Since outcome-analysis estimates are not reported, the clinical interpretation and precision of the primary result remain unavailable.

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("Control", "Bariatric Surgery")
n   <- c(11, 11)
m   <- c(0, 320)
sp  <- c(40, 30)
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  Control  11  0.000  40.000  -26.872  26.872
CARM  Bariatric Surgery  11  320.000  30.000  299.846  340.154

11. Multiplicity, Missing Data and Analysis Populations

The registry lists the breakpoint as the primary outcome and lists Hunger and Body Mass Index as secondary outcomes. The study aim also refers to reward value for sweet, fatty, and vegetable or fruit tastes, but the record does not clarify how those aims relate to the listed outcomes or specify which comparisons were confirmatory. It does not report a multiplicity strategy, such as a hierarchy of tests or an adjustment for examining multiple outcomes. Without that information, the risk of chance findings across several analyses cannot be assessed. No results for the secondary outcomes or the additional taste dimensions are reported.

The registry record does not report a missing-data plan, the amount of missing outcome data, or how missing assessments were handled. It also does not state whether analyses included all enrolled participants, only those with complete measurements, or another analysis population. Although assessment occasions are described, the record does not confirm that each participant completed every scheduled assessment. Missingness can affect interpretation when participants with observed data differ systematically from those without observed data; this is a general concern, not a reported finding in this study.

The record lists zero outcome analyses. As a result, there is no reported analysis population, no account of exclusions from an analysis, and no statistical method to evaluate. The registry also does not report interim analyses, protocol deviations, or sensitivity analyses. These features should be regarded as not reported in the registry record, rather than assumed absent from the conduct of the study.

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 5% reporting threshold.

The safety record lists the Control group with 11 at risk, zero serious adverse events, zero other adverse events, and zero deaths. The Bariatric Surgery group is listed with 11 at risk, zero serious adverse events, zero other adverse events, and zero deaths. These figures describe the registry’s recorded counts for the listed categories.

A zero count in these entries means that no events are recorded in that category for the group as presented. It does not establish that no symptoms or harms of any kind occurred, because the registry does not provide event-term details, ascertainment procedures, severity criteria beyond the serious-event category, or a safety observation window. The list of serious adverse-event terms is empty. The record also does not explain whether the listed at-risk counts cover all enrolled participants or all participants assessed for the primary outcome.

These figures should not be treated as a comparison demonstrating equal safety between groups. The groups are not described as randomized, and the registry does not report an analysis of safety differences or uncertainty around the counts. The safety entries are descriptive registry data, not a complete account of all possible adverse experiences.

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

The registry record establishes that the study set out to examine taste reward in obese patients before and after bariatric surgery, with normal-weight healthy volunteers assessed at two occasions. It identifies the primary measure as the breakpoint in a chocolate-reward task and gives the timing and task procedure. It also lists Hunger and Body Mass Index as secondary outcomes. These details clarify the research question and the operational definition of the principal measure.

It does not establish whether bariatric surgery changed the breakpoint, whether any change differed from changes in the control group, or how precise an estimated difference might be. The registry record contains no outcome-analysis results, numerical endpoint summaries, or uncertainty measures. It therefore supports no conclusion about the direction, size, or statistical strength of an outcome effect. The absence of reported results should not be interpreted as a null result.

Even if a numerical change were available, the design would require careful interpretation. The surgical patients are obese people due to undergo gastric bypass or gastric banding, whereas the controls are normal-weight healthy volunteers. Allocation is not stated. Changes over time in the surgical group could reflect factors other than surgery, and differences between groups could reflect their different characteristics. The registry does not report analyses that address these issues.

The task measures effort for chocolate under a particular set of instructions and escalating response requirements. It cannot by itself establish a broad change in taste perception, eating behavior, or reward across all foods and settings. The study aim mentions sweet, fatty, and vegetable or fruit tastes, but results for those dimensions are not reported. Likewise, the listed secondary outcomes have no posted analysis results in the registry record. The appropriate interpretation is therefore limited to the study design and recorded descriptive information.

14. Why This Trial Matters Statistically

This study raises a statistical question about how to measure a behavioral response to food reward and how that response might change over time. Its primary endpoint is not simply a rating of taste: it uses the effort participants choose to expend to obtain chocolate, with the required effort increasing through the task. That makes the outcome a defined behavioral measure, while also making its interpretation specific to the task conditions.

The repeated assessments are relevant because the study seeks to understand change following surgery rather than only a difference between groups at one occasion. The control group’s repeat assessments could offer context for changes over time. At the same time, the group descriptions underline a central design issue: the comparison is not randomized and the groups differ in weight status and surgical experience. A statistical contrast cannot by itself remove those differences.

The registry also illustrates why a clearly named endpoint is not enough to evaluate evidence. Interpretation depends on the analysis estimate, its uncertainty, the analysis population, missing-data handling, and the relationship between the primary question and other outcomes. Those results and methods are not reported in the registry record. The completion status and safety counts do not fill that gap.

For biostatisticians and clinical researchers, the record is useful as a case in separating the research aim, the operational endpoint, the design, and the available evidence. It also shows why planning calculations based on an observed effect must not be confused with a prospective design justification or observed power. Without reported outcome analyses, the study’s substantive result and statistical precision remain unknown.

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 principal limitation for interpretation is that the registry record reports no outcome analyses. It gives no mean breakpoint, standard deviation, change estimate, confidence interval, or test result. Consequently, the magnitude and precision of any change cannot be evaluated, and no conclusion about the primary endpoint can be drawn from the recorded results.

The comparison is also limited by the groups’ different descriptions. The surgical group consists of obese patients due to undergo gastric bypass or gastric banding; controls are normal-weight healthy volunteers. Allocation is not stated, and the registry’s own comparison note cautions that the arms are not a like-for-like control comparison. The record does not describe adjustment for group differences or provide participant characteristics with which to assess comparability.

The primary task focuses on effort for chocolate. Although the stated aim includes multiple taste categories, the registry does not report corresponding outcome analyses. The task’s click-based breakpoint may not represent broader food preference or behavior outside the experimental setting. The registry also does not report task reproducibility, assessor procedures, or whether the surgical procedures were analyzed separately.

Further details needed to assess the analysis are not reported in the registry record: outcome-specific analysis populations, completeness of repeated assessments, missing-data handling, prespecified statistical methods, multiplicity procedures, and sensitivity analyses. The safety entries are limited to the listed event categories and do not include an observation window or event descriptions. These gaps do not prove that procedures or analyses were absent, but they restrict what can be concluded from the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Investigation of the Effects of Bariatric Surgery on Taste Reward in Humans — NCT01531738.
• Registry record last updated 2020-11-16; status last verified 2020-10.
• Results first posted 2020-10-22.
• 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

NCT01531738 is a completed study sponsored by Imperial College London, with an enrollment of 22. It examines taste-reward measures in obese patients due to undergo gastric bypass or gastric banding and in normal-weight healthy volunteers. Surgical patients were scheduled for assessment 2 weeks before and 8-12 weeks after surgery; controls were scheduled for two occasions 10-14 weeks apart.

The primary outcome is the breakpoint in a chocolate-reward task, measured in clicks and summarized as a mean with standard deviation. Hunger and Body Mass Index are listed as secondary outcomes. The record describes zero serious adverse events, zero other adverse events, and zero deaths in each group as presented.

No outcome analyses are reported in the registry record. The primary result, its uncertainty, missing-data handling, analysis populations, and multiplicity approach are therefore not available for interpretation. Allocation is not stated, and the groups are not a like-for-like control comparison.