Pilot Assessment of an Auto Blood Pressure Monitor: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Pilot Assessment of an Auto Blood Pressure Monitor (NCT02258256), a na na study. The primary outcome is Accuracy of Blood Pressure Measurement by Sphygmo Relative to the Clinical Standard..

2. Clinical Question

The central question is whether blood pressure readings from Sphygmo are similar to readings from the commercially available device used as the clinical standard. The study also aimed to assess device use by nurses. The registry describes repeated measurements during a single study visit lasting up to 24-72 hours, with the timing of measurements determined by the supervising clinician. The primary outcome concerns mean systolic and diastolic pressure, with the device comparison defined as Sphygmo minus the standard.

This is a device-measurement question, not a question about whether a treatment changes a health outcome. The registry also describes documenting alarm indications and assessing usability, but the posted primary outcome is the comparison of measured blood pressure. The record does not report numerical outcome findings or a separate numerical result for usability.

3. Trial Design

The registry classifies this as a completed, single-group device study with no masking and no randomized allocation. Its listed intervention is Sphygmo. Participants were to have blood pressure measured by both Sphygmo and a commercially available device, with the two cuffs placed on opposite arms. Thus, the comparison is within participants rather than between a group assigned to Sphygmo and a separate control group. The registry explicitly cautions that this is not a randomized comparison and that the arms should not be treated as a like-for-like control comparison.

Measurements were to be taken repeatedly during a single study visit, up to 24-72 hours, at intervals determined by the supervising clinician. Monitoring was to continue until it was no longer clinically prescribed. A nurse and a trained research assistant were to record blood pressure readings and document alarm indications from both devices. Clinical decisions were based on the commercially available device, not the research device.

The brief summary says the study planned to enroll 20 women who were at risk of or diagnosed with pre-eclampsia at Queen Elizabeth Central Hospital. The registry lists actual enrollment as 11. The record gives the study status as completed and lists start and primary completion dates of 2015-03-01 and 2017-10-01. The phase is listed as NA; allocation is also listed as NA. The record does not report a randomized sequence, a masking procedure, or an allocation ratio.

The paired measurement arrangement allows the devices to be compared within the same participant, which can account for some differences between people when the analysis is designed accordingly. However, measurements were taken on opposite arms, and the registry does not report an analysis plan addressing any possible arm-related variation. It also does not report a numerical primary outcome estimate, the number of measurement pairs contributing to the outcome, or detailed participant-level results.

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 Accuracy of Blood Pressure Measurement by Sphygmo Relative to the Clinical Standard., measured over Measured during a single study visit, up to 24-72 hours..

The primary endpoint is described as accuracy of blood pressure measurement by Sphygmo relative to the clinical standard. It concerns mean systolic and diastolic blood pressure in mmHg. For each participant, the description says that mean pressure was measured with each device and compared as Sphygmo minus Standard. Measurements were repeated during a single study visit, up to 24-72 hours, with intervals set by the supervising clinician. The posted outcome description says the reported values represent averages across participants.

This type of endpoint is used to characterize how closely a measurement device agrees with a reference device. Comparing the mean readings can describe the direction and size of an average difference, but an average alone does not show how much individual readings vary around that difference. A device could have a small average difference while still showing substantial variation for particular readings or participants. Assessing agreement more fully generally requires information about the distribution of paired differences, not only separate average readings.

The registry states the endpoint and measurement approach, but numerical mean pressures, standard deviations, and the Sphygmo-minus-standard result are not reported in the registry record. It also does not report a numerical endpoint for usability or alarm performance. The stated measurement endpoint therefore identifies what was intended to be assessed, but the record does not give enough numerical results to quantify the observed comparison.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What the endpoint represents. The primary outcome is continuous: blood pressure measured in mmHg. The registry describes systolic and diastolic pressure and specifies a mean for each device. A mean is a measure of the central location of a set of observations. It can make a collection of repeated readings easier to summarize, but it does not show every reading or how widely readings are dispersed. The record identifies standard deviation as the measure of dispersion, but numerical means and standard deviations are not reported in the registry record.

Why the comparison is paired. Each participant was intended to have readings from both Sphygmo and the commercial standard. In general, a paired comparison evaluates the within-participant difference between two measurements, rather than treating the two sets of measurements as independent. This can be informative because people differ in their blood pressure levels. The registry defines the direction of the comparison as Sphygmo minus Standard. A positive difference would mean the Sphygmo value is higher under that definition, and a negative difference would mean it is lower; these are general interpretations, not findings from this study. The registry does not provide the numerical differences.

Paired analysis depends on having suitable matched observations and a method that reflects the design. Here, cuffs were placed on opposite arms. The registry does not state whether device placement was switched between arms, whether arm assignment was randomized, or how the analysis would address possible arm differences. It also does not state whether the comparison used one participant-level mean per device, all repeated readings, or another summary. Although the outcome description says participant means were compared and values averaged across participants, a detailed statistical procedure is not reported.

Repeated measurements and dependence. Multiple readings from the same person are generally related: readings from one participant are not necessarily independent observations. A statistical method that treats every reading as independent can understate uncertainty when measurements within a participant are correlated. General methods for this setting include summarizing measurements at the participant level or using models that account for clustering within participants. The registry does not report which method was used, how many repeated readings were collected, or how incomplete sequences were handled. The stated timing was determined by the supervising clinician, so the record does not establish that all participants had the same number or schedule of readings.

Means, variability, and agreement. A comparison of average values is useful for detecting an average offset between devices, but device agreement is broader than equality of group means. In general, a distribution of paired differences helps show whether the average difference reflects readings that are consistently close or a mix of larger positive and negative discrepancies. Standard deviations describe spread around a mean, but the registry does not report numerical variability for the primary outcome. No agreement limits, graphical assessment of paired differences, or other agreement statistics are reported in the registry record.

A confidence interval is a general statistical tool for expressing uncertainty in an estimated quantity. For a mean difference, it conveys how precisely the average difference has been estimated under the chosen analysis and its assumptions. A narrow interval indicates greater precision than a wide interval, but does not by itself establish clinical acceptability. The registry record does not report a confidence interval for the device comparison, so the precision of the primary result cannot be evaluated from the posted information. A p-value, if reported, would address a different question about compatibility with a specified null model; it would not by itself quantify agreement or practical importance. No p-value is reported for the primary endpoint.

Over-dispersion and count outcomes. General count-data methods often assume a particular relationship between the mean and variance. Over-dispersion occurs when observed variability exceeds that assumed by a model, which can make conventional uncertainty estimates too optimistic if not addressed. This concept could matter for outcomes such as numbers of alarms or events, but the primary endpoint is continuous blood pressure, and the registry does not report a count-based analysis of alarms. No model for alarm indications is reported. Consequently, over-dispersion is a general consideration rather than a stated analysis feature of this record.

Sample-size illustrations. The posted planning assumptions describe illustrative calculations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The stated effect to detect is a fraction of the observed effect. These are planning illustrations, not observed power and not evidence that the original study was designed with those assumptions. The registry does not report its own sample-size justification. The assumed equal allocation between two arms also differs from the registry's single-group, within-participant measurement design, so those calculations should not be mistaken for a description of how participants were assigned in this study. The numerical observed effect and resulting planning estimates are not reported in the registry record.

Analysis choices that remain unclear. The registry does not report a prespecified statistical analysis plan, handling of missing readings, analysis populations, treatment of repeated measurements, or an approach to multiple outcomes. It lists one primary outcome measure and zero analyses. The absence of reported methods prevents assessment of whether the analysis fully reflected the paired and repeated-measure structure. This is a limitation of what can be interpreted from the registry record, not evidence that any particular method was or was not used outside the record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure, focused on the mean systolic and diastolic pressures measured by Sphygmo and the commercial standard. It also describes aims concerning usability and alarm indications. The record does not report a statistical analysis plan specifying which outcomes were tested, how they were ordered, or whether any adjustment for multiple comparisons was planned. It lists zero analyses. Therefore, the handling of multiplicity is not reported in the registry record. General statistical practice recognizes that testing several outcomes or analyses can increase the chance of finding an apparently unusual result by chance; whether that concern applies to any reported inference cannot be assessed without the analysis details.

Missing-data handling is also not reported. The study description anticipates repeated measurements over a clinician-determined period, but does not say how missing readings, early discontinuation, incomplete device pairs, or participants with partial measurement sequences were handled. The listed enrollment is 11, but the record does not state the number of complete paired outcome records. This matters because a comparison based only on complete pairs can represent a different subset from all enrolled participants if data are incomplete.

The registry does not define an analysis population, such as all enrolled participants or only participants with usable measurements. It does not report exclusions or reasons for missing data. The number of analyses is listed as zero, and numerical primary outcome estimates are not reported. As a result, neither the population used for analysis nor the effect of missingness on the comparison can be evaluated. These reporting gaps should not be filled by assumptions about the protocol or statistical plan.

11. 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.

The registry safety record lists 11 preeclamptic women at risk for serious adverse events and zero affected by a serious adverse event. For other adverse events, it lists 11 at risk and zero affected. Deaths are listed as zero. These are event counts in the registry record; they do not provide a detailed account of how events were defined, collected, reviewed, or attributed.

A zero count means that no events of the listed kind were recorded for the stated group in this record. It does not establish that the risk of an event is absent, particularly in a small pilot study. The registry lists enrollment of 11, but does not provide participant-level safety follow-up details or a separate duration of safety observation. The primary measurement period is described as a single study visit, up to 24-72 hours; the record does not establish that this was the full safety follow-up period.

The safety entries do not quantify measurement accuracy, usability, or alarm performance. They should be read separately from the primary device-comparison outcome, whose numerical results are not reported in the registry record.

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

This registry record establishes that a pilot device assessment was conducted and describes how the two blood pressure monitors were intended to be compared. Participants were to be measured with both Sphygmo and a commercially available standard, using cuffs on opposite arms. The primary comparison was defined as Sphygmo minus Standard for mean systolic and diastolic pressure. The design is single group, without masking, and is not described as a randomized comparison.

The record does not report the numerical primary outcome values. It therefore does not show whether Sphygmo readings were higher or lower on average, how large any difference was, or how precise an estimate might be. It also does not give the spread of paired readings needed to assess the range of individual agreement. Without those results, it is not possible to judge from the registry whether the device met any accuracy threshold. The registry does not report such a threshold either.

The record also does not provide numerical usability findings, alarm results, or a detailed statistical analysis. The stated goal of assessing whether the monitor is easy for a nurse to use is an aim, not a reported finding. Likewise, the study's intended use in settings where automatic blood pressure monitoring is limited or unavailable is context for the research question, not evidence of device performance in those settings.

The safety record lists zero serious adverse events, zero other adverse events, and zero deaths among the stated group of 11 at risk. Those counts are limited to the entries and follow-up information in the registry record; they do not establish absence of risk. The brief summary describes intended enrollment of 20, while the registry lists enrollment of 11, and the reason for that difference is not reported.

In short, the record describes a pilot comparison but does not provide the outcome estimates needed to quantify its result. It supports no conclusion about the degree of agreement, the precision of the comparison, or the usability of the device. Those points remain unresolved in the registry record.

13. Why This Trial Matters Statistically

This study raises statistical issues that are central to evaluating measurement devices. The same participant was to be measured with both devices, making the intended comparison paired. That structure can be more informative than comparing separate groups because each person serves as their own reference. Correct analysis still needs to respect the pairing and the repeated measurements within participants. The registry describes the measurement arrangement but does not report the statistical methods used.

The outcome also illustrates why a comparison of averages is not the whole story in device assessment. An average difference can identify a systematic offset, but it cannot by itself show whether individual paired readings are close or whether some differences are large. A useful evaluation therefore needs both a measure of central difference and information about its variability and uncertainty. The registry specifies mean and standard deviation as outcome summaries, but does not report their numerical values.

The opposite-arm setup adds an important design consideration. In a general paired device study, differences between the measurement sites could contribute to observed differences between devices. The registry does not report whether device positions were switched, or how any arm-related variation was addressed in the analysis. This makes transparent reporting of the allocation and analysis procedures especially important for interpreting a device comparison.

The pilot context also matters. The registry lists enrollment of 11, while the brief summary describes a planned enrollment of 20. The record does not provide an original sample-size justification, and the planning illustrations based on an observed effect are not a substitute for that justification. They are not observed power. Most importantly, the record does not report primary outcome estimates, so precision and agreement cannot be evaluated from the posted results.

These are not merely technical details: they determine what a reader can infer from a measurement study. A clear account of paired differences, variation, missing readings, and analysis methods would allow readers to distinguish an average offset from agreement across individual measurements. Those details are not reported in the registry record.

14. 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 interpretation is that numerical results for the primary endpoint are not reported in the registry record. The outcome description identifies mean systolic and diastolic pressure and the Sphygmo-minus-standard comparison, but gives no means, standard deviations, difference estimate, or uncertainty interval. Device agreement and its precision therefore cannot be quantified from the record.

The registry lists enrollment of 11, whereas the brief summary describes an intended enrollment of 20 women. It does not explain the difference or report how many participants had complete paired data. Because measurements were repeated at clinician-determined intervals and monitoring continued until no longer clinically prescribed, the number and timing of readings may have differed across participants; the record does not give those details.

Measurements were to be taken on opposite arms. The record does not state whether the device-to-arm assignment was varied or randomized, or how a statistical analysis would account for possible arm-related differences. It also does not describe the handling of within-participant dependence from repeated readings. No detailed statistical analysis plan, missing-data method, or analysis population is reported.

The study was single group, with no masking and no randomized allocation, and the registry cautions that the comparison is not a like-for-like control comparison. The commercial device was used for clinical decisions, while Sphygmo was the research device. The record does not report numerical usability or alarm findings. These limitations restrict what can be inferred from the registry; they do not establish what procedures or analyses may have been performed outside the record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Pilot Assessment of an Auto Blood Pressure Monitor — NCT02258256.
• Registry record last updated 2021-08-10; status last verified 2021-08.
• Results first posted 2018-12-21.
• 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.

18. Record Summary

This completed pilot study assessed Sphygmo, an automatic blood pressure monitor, against a commercially available clinical standard in women at risk of or diagnosed with pre-eclampsia. The registry describes a single-group, unmasked design in which each participant was to have both devices used on opposite arms, with repeated measurements during a single study visit lasting up to 24-72 hours. Clinical decisions were based on the commercial device.

The registry lists enrollment of 11; the brief summary describes an intended enrollment of 20 at Queen Elizabeth Central Hospital in Malawi. The primary outcome was the comparison of mean systolic and diastolic pressure, defined as Sphygmo minus Standard. Numerical primary results, detailed analysis methods, usability findings, and alarm results are not reported in the registry record. The safety entries list zero serious adverse events, zero other adverse events, and zero deaths among the stated group of 11 at risk.