Sensory Effects of Rapidly-Changing Magnetic Fields: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Sensory Effects of Rapidly-Changing Magnetic Fields (NCT01632800), a na na study. The primary outcome is Degree of Discomfort Under Applied Pulsed Magnetic Fields.

2. Clinical Question

The study description places the question in the context of magnetic resonance imaging: shorter magnetic pulses had been considered as a way to reduce unpleasant sensations, and the study was intended to explore whether the proposed effect also held when very short pulses were applied. This is the rationale recorded for the research, not a finding from the study. The registry record describes escalating exposure and repeated questioning, rather than a randomized comparison of pulse durations. It therefore does not provide a direct between-group estimate of whether one pulse approach causes less discomfort than another.

For each pulse, participants were asked whether they noticed a sensation, with examples including tingling or tapping, and were asked to rate it on a scale from 0 to 4. The scale distinguishes no sensation, barely noticeable sensation, easily noticeable sensation, unpleasant sensation, and very unpleasant sensation. The registry record does not explain which ratings counted toward the registered percentage of participants with discomfort. That operational definition, along with any observed result, is not reported in the registry record.

3. Trial Design

This was a completed, single-group device study of high pulsed magnetic fields. The registry lists an enrollment of 26, a start in 2011-08, and primary completion in 2011-10. The study phase is recorded as NA. The allocation field is also NA, consistent with the record describing no randomized allocation, and masking is listed as NONE. No parallel control arm is described.

The arm description says that each subject would undergo escalating exposure to the magnetic field. The primary outcome description says pulsed magnetic fields were applied a total of forty-eight times to the right hand of each subject. After each magnet coil pulse, the participant was asked whether a sensation was noticed and to rate it. Bioeffects were to be assessed within the five-minute application of each pulse sequence. The record does not specify the detailed pulse parameters, the exact escalation schedule, or how long a participant remained at any particular exposure level.

A single-group design can describe responses observed during exposure, but it does not by itself separate an exposure effect from other explanations for a response. For example, without a distinct control condition, the study does not supply a randomized contrast between magnetic pulse regimens. The registry record does not report a control condition or a prespecified comparison between exposure levels. It also does not give enough information to establish how the sequence of escalating exposures was incorporated into an outcome analysis.

The completed status indicates that the study is recorded as completed, but completion alone does not establish that an outcome result was reported. The registry lists one primary outcome measure and zero analyses. The statistical analysis plan, sample-size justification for the trial, and details of any planned interim analyses are not reported in the registry record. Planning illustrations based on an observed effect, if presented separately, are not evidence that those sample sizes were used in this study or that the effect was observed.

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 Degree of Discomfort Under Applied Pulsed Magnetic Fields, measured over Bioeffects will be assessed within the five-minute application of each pulse sequence.

The registered primary endpoint is the percentage of subjects with discomfort under applied pulsed magnetic fields. Its stated unit is a percentage of subjects with discomfort, and its parameter is listed as NUMBER. The description gives the assessment procedure: after each pulse, participants were asked whether they noticed a sensation and then asked to rate it from 0 to 4. The examples of sensation are tingling and tapping. The scale runs from no sensation through barely noticeable, easily noticeable, unpleasant, and very unpleasant sensation.

In general, a participant-level percentage can provide a concise summary of how many people meet a specified event definition. It differs from a summary of the intensity of all ratings or a summary of responses across every exposure. Here, the registry record does not state the rule used to classify a participant as having discomfort. In particular, it does not say which scale ratings count as discomfort, or how responses across repeated pulses were combined into one participant-level outcome. That distinction matters because the description collects repeated responses from each participant, whereas the endpoint is expressed as a percentage of participants.

The endpoint is relevant to the study’s stated focus on sensory effects during magnetic-field exposure. However, the registry record does not report the observed percentage, the number of participants meeting the endpoint definition, or an estimate of uncertainty around that result. The recorded assessment plan alone cannot establish the frequency or severity of discomfort observed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registered outcome is a participant-level percentage, but the assessment procedure collects repeated ratings within each participant. These are different levels of data. In general, a percentage of participants with an event treats each participant as the unit in the summary. A repeated-response analysis instead uses information from multiple observations per participant and must account for the fact that those observations are related. The registry record does not say which analytical approach was used, and it lists zero analyses.

What does the outcome definition require?

A binary percentage requires a rule that classifies each participant as either meeting or not meeting the event definition. In this study, participants were asked whether they noticed a sensation and then rated the sensation on a scale from 0 to 4. The endpoint is described as the percentage with discomfort, but the record does not state which response or rating qualifies as discomfort. It also does not explain whether a participant is counted if the qualifying response occurs after any one pulse, after a particular exposure, or according to some summary across pulses. Without that rule, the named measure is not fully operationalized in the registry record.

In general, a binary summary is straightforward to interpret when its event definition is clear: it describes the share of participants who meet that definition. It can, however, discard detail in an ordinal rating scale. A summary that distinguishes levels of sensation could retain information about intensity, whereas a binary endpoint compresses multiple response levels into a yes-or-no classification. The record does not report a separate analysis of the full rating scale, so it is not possible to know whether such information was analyzed.

Why do repeated responses matter?

Each participant was to be asked about sensations after repeated pulses, with exposure escalating over the course of the study. In general, responses from the same person may be more alike than responses from different people. Treating every pulse response as if it came from a separate, unrelated participant can make uncertainty estimates too narrow. Methods for repeated or clustered data account for within-participant dependence, while a participant-level summary can avoid treating each response as independent by first defining one outcome per person. The registry record does not identify the method used or explain how repeated assessments were reduced or modeled.

Escalating exposure also means the order of observations is relevant to interpretation. In general, changes across sequential assessments can reflect the exposure level, the order in which exposures occurred, or other time-related factors. A prespecified analysis can clarify which comparison is intended and how the order is handled. No such analysis plan is reported in the registry record. The entry does not state whether exposure-specific response patterns were to be compared or whether only an overall participant-level percentage was intended.

What can the design estimate?

A single-group study can describe observations in the participants who underwent exposure. It does not create a randomized contrast with an untreated or alternative-exposure group. In general, a causal comparison requires a defensible counterfactual: an estimate of what would have happened to comparable participants under a different condition. Randomized groups can support that comparison by balancing factors on average, while a single group does not offer the same direct protection against alternative explanations. In this study, the record lists one arm and no randomized comparison, so no comparative treatment effect is reported.

The record gives no confidence interval, standard error, hypothesis test, or model estimate for the primary outcome. In general, a point estimate indicates the estimated magnitude, while an interval communicates precision under the chosen method. A p-value addresses compatibility with a specified null model and assumptions; it is not a measure of clinical importance or a substitute for an effect estimate. Since no outcome analysis is listed, none of these inferential quantities can be interpreted for the primary endpoint.

What do the planning assumptions mean?

The planning-illustration description specifies a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. It also says that non-time-to-event illustrations are expressed as participants per arm. These are planning assumptions, not observed trial findings. The registry describes this study as single-group, so the two-arm equal-allocation assumption does not describe its registered design. The sample-size justification used to plan this trial is not reported in the registry record. No specific planning sample-size values or observed-effect estimate are stated in the record presented for this analysis.

In general, sample-size calculations ask how much information a future design might need to detect a specified effect under stated assumptions. They do not establish that an effect occurred, and they are not a retrospective measure of the probability that a completed study found a true effect. A planning illustration is not observed power. Its relevance depends on whether its assumed design, endpoint, effect size, and analysis match the study being considered. Here, the registered study is a single group, while the stated illustration assumes allocation between two arms, so the illustration should not be treated as a description of how this trial was analyzed.

Finally, the registry record does not report whether the planned statistical methods were changed, whether an interim analysis occurred, or how analysis populations were defined. Those omissions limit the ability to assess alignment between an intended analysis and any results. Since no primary analysis is listed, the record supports a description of the assessment plan and design, but not statistical inference about the sensory outcome.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Single Arm Study")
n      <- c(25)
events <- c(0)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Single Arm Study  25  0  0.0  0.0  13.7  0.0  13.3  0.1  13.2

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure and zero analyses. It does not report a statistical analysis plan, a list of secondary outcomes, a hierarchy of hypotheses, or procedures for controlling multiplicity. Therefore, it is not possible to determine whether multiple outcomes or repeated comparisons were planned, or whether any adjustment for multiple testing was intended.

In general, multiplicity arises when several hypotheses or comparisons are evaluated. Looking at many results can increase the chance of finding an apparently notable result by chance, so an analysis plan may identify a primary comparison or use an adjustment. Repeated sensory assessments could also support many possible summaries, such as responses by pulse or exposure level, but the registry does not report which, if any, were analyzed. No claim about multiplicity adjustment can be made from the record.

Missing-data handling is not reported in the registry record. The entry does not state how incomplete sensory ratings, missed assessments, withdrawals, or unavailable endpoint classifications were handled. The reason the adverse-event listing has 25 participants at risk when enrollment is 26 is also not reported. This difference alone does not establish that a participant withdrew or that any particular outcome was missing.

Analysis populations are not described. The record does not identify an intention-to-treat population, a per-protocol population, or another analysis set for the sensory endpoint. In general, analysis-population definitions describe which participants contribute to a particular estimate and how deviations or incomplete follow-up are treated. Without those definitions or an outcome analysis, the denominator and handling of missing sensory responses cannot be assessed.

12. 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.

The adverse-event listing reports 0 serious adverse events among 25 participants at risk in the single-arm group. It also reports 0 other adverse events among 25 at risk. No serious adverse-event terms are listed. Deaths are not reported in the registry record; a null entry should not be read as a stated count of zero.

These figures describe what is entered in the registry for the listed group. They are not an estimate of the registered primary sensory endpoint, which concerns the percentage of participants with discomfort during magnetic-field exposure. The adverse-event listing does not explain how events were defined, how actively they were collected, or the observation period for the event counts. Those details are not reported in the registry record.

In general, a count of zero observed events does not establish that an event is impossible or that risk is absent. Its interpretation depends on the number of people observed, the duration and completeness of follow-up, and the event-collection methods. No additional rate, interval, or comparative safety estimate is reported. The record lists enrollment of 26 overall but 25 at risk for the adverse-event group; the reason for that difference is not reported in the registry record.

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

The registry record establishes that a completed single-group study was designed to assess sensations during escalating exposure to high pulsed magnetic fields. Participants were asked about sensations after repeated pulses to the right hand and rated them on a scale from 0 to 4. The registered primary measure is the percentage of participants with discomfort. These details describe the research question and assessment procedure.

The record does not report the observed primary endpoint or an analysis of it. It therefore does not establish how many participants experienced discomfort, how intense their sensations were, or how responses varied across exposures. It also does not report a direct comparison between pulse regimens. The study rationale concerning shorter magnetic pulses should not be mistaken for a result showing that shortening pulses changed sensory effects.

The absence of a reported analysis is not evidence that there was no discomfort, nor is it evidence that discomfort occurred. It means the outcome cannot be quantified from the registry record. The endpoint’s classification rule is not reported, which further limits interpretation: the description collects ratings across five response levels, but does not state how these become the stated participant-level percentage.

The adverse-event entries list zero serious and zero other adverse events among 25 at risk, but those entries are a separate registry summary and do not fill the gap in the sensory endpoint results. The listed figures also do not support a broad conclusion that no adverse effects occurred, particularly because event definitions and collection methods are not reported. Overall, the record supports a description of a small, single-group exposure study and its intended sensory assessment. It does not support a claim about the observed frequency of discomfort, a causal effect of pulse duration, or a comparative estimate of safety.

14. Why This Trial Matters Statistically

This study illustrates an important distinction between registering an outcome and reporting its result. The registry defines a primary measure as the percentage of participants with discomfort and describes how sensations were to be elicited and rated. Yet it lists zero analyses and gives no observed result for that measure. The existence of a detailed measurement description does not, by itself, provide statistical evidence about the outcome.

The endpoint also highlights the importance of matching the level of measurement to the level of analysis. Responses were collected repeatedly from each participant, while the primary measure is expressed at the participant level. A clear rule for combining repeated ratings into a participant-level event is necessary for the percentage to have a reproducible meaning. The registry record does not report that rule. That is a statistical interpretation issue, not merely a matter of presentation.

The single-group, escalating-exposure structure provides another useful lesson. Repeated observations can describe what participants reported during exposure, but without a comparator they do not directly estimate what would have happened under a different pulse condition. The study’s stated motivation concerns whether an effect seen with shortened pulses holds for very short pulses, but the registered design and missing analyses do not yield a reported comparative estimate.

Finally, the safety entries show why counts need context. Zero listed events is a factual registry entry for the specified group and denominator, but it is not the same as a precise estimate that risk is absent. The record gives limited information about event definitions and follow-up, and it does not explain why the adverse-event denominator differs from overall enrollment. Reading these elements carefully keeps design, measurement, analysis, and interpretation distinct.

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 most direct limitation of the registry record is that it lists no outcome analyses. There is no reported estimate for the primary measure, no uncertainty interval, and no inferential test. Accordingly, the central sensory outcome cannot be quantified from this record.

The endpoint description does not fully state how discomfort was classified. Participants were asked whether they noticed a sensation and were given a 0-to-4 rating scale, but the registry does not specify which ratings count as discomfort or how responses across repeated pulses were combined. It also does not report whether ratings were analyzed by exposure level, by participant, or using another approach.

The study is described as single-group, unmasked, and without randomized allocation. No control condition is listed. Thus, the record does not provide a randomized comparison of different pulse approaches. The escalating sequence and repeated assessment may be informative descriptively, but the registry does not report how sequence or exposure order was handled analytically.

Further details needed to evaluate statistical validity are not reported in the registry record. These include the statistical analysis plan, trial sample-size justification, missing-data methods, analysis-population definitions, and any interim analyses. Eligibility criteria and detailed exposure parameters are also not given in the record. The adverse-event listing uses 25 at risk, while enrollment is 26; the reason for this difference is not reported. Event definitions and the safety observation period are not reported either.

These limitations concern what can be concluded from the registry record and do not establish that the underlying study collected no additional information. They mean that the registered description and the posted adverse-event counts are insufficient to assess the magnitude, precision, and analysis of the intended primary sensory outcome.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Sensory Effects of Rapidly-Changing Magnetic Fields — NCT01632800.
• Registry record last updated 2019-10-08; status last verified 2019-10.
• Results first posted 2016-06-15.
• 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

NCT01632800 is a completed, single-group study titled Sensory Effects of Rapidly-Changing Magnetic Fields. The registry lists enrollment of 26, a start in 2011-08, primary completion in 2011-10, no masking, and a device intervention of high pulsed magnetic fields. The arm description specifies escalating exposure.

The primary outcome concerns the percentage of participants with discomfort. Participants were to receive repeated pulses to the right hand, report whether they noticed a sensation, and rate it from 0 to 4. The registry lists one outcome measure but zero analyses. The observed sensory outcome, its uncertainty, and the statistical analysis plan are not reported in the registry record.

The single-arm adverse-event entry lists 0 serious and 0 other adverse events among 25 at risk. No serious terms are listed, and deaths are not reported in the registry record. The reason for the difference between overall enrollment and the adverse-event denominator is not reported.