Effectiveness and Safety Study of the Dexcom G4™ Continuous Glucose Monitoring System: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effectiveness and Safety Study of the Dexcom G4™ Continuous Glucose Monitoring System (NCT01514292), a na na study. The primary outcome is CGM Relative Differences to Laboratory Reference.

2. Clinical Question

3. Trial Design

The registry describes NCT01514292, “Effectiveness and Safety Study of the Dexcom G4™ Continuous Glucose Monitoring System.” It lists DexCom, Inc. as the sponsor and the study status as completed. The recorded start is 2011-12, and primary completion is 2012-02. The phase is listed as NA.

The design is single group, with enrollment listed as 72. The group is described as using the real-time continuous glucose monitoring system for 7 days. The intervention is a device, identified as continuous glucose monitoring of glucose levels (Dexcom). The brief summary specifies intended use as an adjunct to blood glucose testing among people >18 years-old with diabetes mellitus.

Allocation is listed as NA, and masking as none. This is not a randomized comparison, and the registry explicitly cautions that the arms are not a like-for-like control comparison. The YSI laboratory reference served as the benchmark for glucose measurements, rather than as a second trial arm. Accordingly, the design can characterize device readings relative to the reference but does not establish a between-group treatment contrast.

The registry lists one outcome measure and one analysis. It does not report further details about the analysis population, measurement schedule, handling of repeated readings, or statistical model. Although the study is marked completed, the numerical primary outcome is not reported in the registry record. Completion status should therefore not be mistaken for a complete account of the 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.

Population: Type 1 Diabetes and Type 2 Diabetes with Insulin treatment.

6. Primary Endpoint

The registry lists the primary outcome as CGM Relative Differences to Laboratory Reference, measured over 7 days.

The primary endpoint is titled “CGM Relative Differences to Laboratory Reference.” It measures relative differences, expressed as a percentage, between a CGM glucose value and a laboratory reference YSI glucose measurement. The timeframe is 7 days. The listed summary measure is the mean, with standard deviation as the dispersion measure.

This type of endpoint is used to describe how device measurements compare with a reference method. In general, a difference-based measure can convey the direction and typical size of disagreement, while a measure of dispersion describes how much the observed differences vary. These are distinct aspects of performance: an average alone does not show whether individual differences are tightly grouped or widely spread.

The brief summary also identifies point and rate accuracy as performance interests. The listed primary outcome, however, is a mean of relative differences; the registry does not provide a numerical estimate, its standard deviation, or a separate numerical rate-accuracy result. The calculation formula, including how the relative difference was defined, is not reported in the registry record. Without those details and the outcome values, the endpoint’s numerical magnitude and precision cannot be interpreted.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry classifies the primary outcome as continuous and identifies its summary parameter as a mean, with standard deviation for dispersion. The following explanations are general statistical context, not a description of undocumented procedures used in this study.

What does a mean summarize?

In general, a mean combines observed values into an average. For a difference-based endpoint, that average can summarize the typical direction and magnitude of differences under the chosen calculation. Its meaning depends on how each difference is defined: changing which measurement is subtracted from the other, or using a different denominator for a relative difference, can change interpretation. The exact formula is not reported in the registry record, so the sign convention and calculation cannot be specified.

A mean can also conceal variation across observations. A set of differences may cluster closely around its average or may vary substantially. The mean alone cannot distinguish those patterns. The registry lists standard deviation as the dispersion measure, but its numerical value is not reported. Without it, the record does not show how variable the measured differences were around their average.

What does the standard deviation describe?

In general, standard deviation measures the spread of observations around their mean, in the scale of the measure being summarized. A smaller standard deviation indicates less spread in the observed values, while a larger one indicates more spread. It is not the same as a confidence interval: standard deviation describes variation in observations, whereas a confidence interval describes uncertainty about an estimated quantity under specified assumptions. No numerical standard deviation or confidence interval for the primary endpoint is reported in the registry record.

For device-reference comparisons, variability matters because an average difference does not by itself describe how individual readings compare with the reference. Even when an average is near a chosen target, readings can differ from one another. Conversely, the average may reflect a consistent directional difference. These are general considerations; the registry record does not provide numerical results that would show which pattern occurred in this study.

How does a reference measurement differ from a control group?

YSI laboratory reference measurements are the benchmark named for assessing CGM glucose values. In general, paired device and reference measurements can be used to describe agreement between methods. That is a measurement comparison, not the same question as whether one randomized treatment group has a better clinical outcome than another. The registry describes a single-group study and does not report a concurrent control arm.

When many measurements are taken from a participant, those measurements may be correlated rather than statistically independent. General statistical methods need to account for such clustering when estimating uncertainty; treating correlated readings as independent can make uncertainty appear smaller than it is. The registry record does not report the number or timing of measurements per participant, how repeated measurements were handled, or the model used for analysis. It is therefore not possible to determine which approach was used.

What do point and rate accuracy mean?

In general, point accuracy concerns how a device reading compares with a reference at a particular measurement point. Rate accuracy concerns how well a device reflects change over time. These questions involve different features of measurements. The study brief identifies both as performance interests, but the registry’s listed primary outcome is relative differences in glucose values. Separate definitions and numerical results for rate accuracy are not reported in the registry record.

What can planning assumptions tell readers?

The registry describes a sample-size planning illustration based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It states that the effect to detect is a specified fraction of the observed effect. These are planning assumptions, not evidence that the trial itself used that design: the actual study is single group, and no two-arm randomized comparison is reported. The numerical primary effect is not reported in the registry record, so the planning illustration cannot be interpreted as a result about observed performance. Such sample-size illustrations are hypothetical planning quantities, not observed power and not a substitute for an estimate with its uncertainty.

The statistical analysis plan, including any model, assumptions, confidence-interval method, and decision thresholds, is not reported in the registry record. No particular method should be attributed to the investigators on the basis of the endpoint description alone.

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("Real Time Continous Glucose Monitoring System")
n   <- c(72)
m   <- c(13)
sp  <- c(6)
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  Real Time Continous Glucose Monitoring System  72  13.000  6.000  11.590  14.410

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and one analysis. That information does not establish whether the study had additional outcomes or analyses outside the listed registry entry, or whether any multiplicity procedure was planned. The statistical plan and any adjustment for multiple testing are not reported in the registry record.

Multiplicity matters in general when several hypotheses or outcomes are tested: the chance of at least one apparently notable result can increase as the number of tests grows. How to address that issue depends on the prespecified analysis plan and the goals of the study. Neither a testing hierarchy nor a multiplicity adjustment is reported in the registry record, so no claim about their use is warranted.

The record does not report how missing glucose readings or incomplete participant observations were handled. It also does not describe exclusions, imputation, sensitivity analyses, or the number of observations contributing to the primary outcome. These omissions matter because the analyzed data may differ from the data intended for collection, and methods for handling missing values can affect estimates and uncertainty.

The analysis population is not reported in the registry record. It is not specified whether the primary result was intended to include all participants who began device use, those with complete measurements, or another defined group. Enrollment is listed as 72, but that figure alone does not identify who contributed data to the endpoint analysis.

For a continuous endpoint, a complete statistical account would ordinarily make clear the analysis population, the summary estimate, its dispersion or uncertainty, and the handling of incomplete data. Those details are not reported in the registry record. Consequently, the single listed analysis cannot be taken as evidence that missingness or multiplicity was absent; the record simply does not describe those methods.

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 5% reporting threshold.

The safety entry concerns the CGM Device group and lists 72 at risk for serious adverse device effects and 72 at risk for other adverse device effects. It records zero affected for each category. These are the counts recorded for this group; the registry record does not provide event terms for serious adverse effects.

A count of zero affected means that no affected participants are entered in that registry category. It does not, by itself, establish that every possible device-related harm was ruled out or that the risk is zero. Interpretation depends on how events were defined, collected, attributed, and followed. Those operational details are not reported in the registry record.

The deaths field is null, so a death count is not reported in the registry record; it should not be read as a recorded zero. The record also does not provide timing, severity details beyond the categories, or a narrative account of safety events. The counts describe the registry entry and should not be extended beyond its stated group and categories.

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

The record establishes that the study was designed to characterize Dexcom G4 system performance relative to YSI laboratory reference measurements and to characterize adverse device effects during 7 days of use. It specifies a continuous primary endpoint based on mean relative differences, a standard deviation as the dispersion measure, and a single-group design. The recorded safety counts show zero affected in the serious and other adverse device effect categories.

It does not report the numerical primary endpoint or its standard deviation. Therefore, the record does not show the average relative difference, the variability of those differences, or the precision of an estimate. It also does not report a confidence interval or a separate numerical result for rate accuracy. No conclusion about meeting a performance standard can be drawn from the endpoint description alone.

The study design also sets a boundary on interpretation. A laboratory reference can anchor a measurement comparison, but the single-group study is not a randomized comparison of treatments. The registry does not establish comparative effects against another device or care strategy. The brief summary’s description of use as an adjunct to blood glucose testing does not create a separate comparator group.

Likewise, zero recorded adverse device effects in the listed categories is not the same as proof that no harm is possible. The registry does not report event ascertainment details, and the deaths field is not populated with a numerical count. Safety interpretation should remain limited to the categories and counts recorded.

Overall, the registry describes the question and design but leaves the principal numerical performance result unavailable. That is a reporting limitation, not a result of zero difference, no variability, or no effect. The record supports a description of what was assessed, but not a quantitative judgment about the magnitude or precision of device-reference agreement.

14. Why This Trial Matters Statistically

This trial illustrates a distinction that is central to biostatistics: measuring agreement with a reference method is not the same as comparing clinical outcomes between randomized groups. The study’s primary objective concerns device performance relative to YSI measurements, and its design is single group. That structure determines what questions the data can address.

The endpoint also highlights why a mean and a measure of dispersion serve different purposes. A mean relative difference would summarize an average, while the standard deviation would describe the spread of observed differences. Both are useful for interpreting measurement performance, but neither numerical result is reported in the registry record. Without them, the main statistical question remains quantitatively unanswered.

Repeated measurements can raise further design and analysis issues. In general, observations from the same participant may be correlated, and analyses should reflect that dependence when estimating uncertainty. The registry does not describe the measurement schedule or method for handling repeated observations. This makes the record a useful reminder that an endpoint label and summary-statistic type do not fully specify an analysis.

The record also shows why status and safety counts must be kept separate from efficacy interpretation. The study is marked completed, and its safety entry records zero affected in the listed categories, but neither fact supplies the missing primary accuracy estimate. A completed study can still have incomplete result reporting in a registry record.

For clinical researchers, the key statistical lesson is to distinguish the study question, the measurement reference, the analysis design, and the reported estimate. Each contributes a different part of interpretation. When numerical results and methods are missing, conclusions should remain correspondingly limited.

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 is that the registry does not report the numerical primary outcome, despite identifying its measure, unit, timeframe, and summary-statistic type. The mean relative difference and standard deviation are not reported in the registry record. Confidence intervals and p-values are also not reported, so neither the magnitude nor statistical precision of the primary result can be assessed.

The study is single group, with allocation listed as NA and masking listed as none. A YSI reference supports measurement comparison but does not provide a randomized control arm. The design therefore cannot answer a like-for-like comparative treatment question. The brief summary identifies point and rate accuracy, but separate numerical results for rate accuracy are not reported.

The evaluation timeframe is 7 days. The registry does not report longer-term performance or safety information. It also gives limited detail about the intended population beyond people >18 years-old with diabetes mellitus; diabetes type, participant characteristics, and subgroup results are not reported in the registry record.

Important analysis details are missing, including the relative-difference formula, measurement schedule, handling of repeated observations, analysis population, missing-data methods, and statistical analysis plan. The recorded enrollment of 72 does not establish how many observations contributed to the primary analysis. The deaths field is null rather than a numerical count, and event-collection details are not reported.

These limits arise from the information in the registry record and should not be mistaken for proof that the study did not collect further information. They do mean that the posted registry information alone cannot support a detailed quantitative assessment of accuracy, uncertainty, or longer-term safety.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Effectiveness and Safety Study of the Dexcom G4™ Continuous Glucose Monitoring System — NCT01514292.
• Registry record last updated 2015-10-05; status last verified 2015-08.
• Results first posted 2015-10-05.
• 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

NCT01514292 is a completed, single-group device study sponsored by DexCom, Inc. The registry lists enrollment as 72, the study start as 2011-12, primary completion as 2012-02, and the phase as NA. Participants were to use the Dexcom G4 real-time continuous glucose monitoring system for 7 days as an adjunct to blood glucose testing.

The primary endpoint is the mean relative difference, expressed as a percentage, between CGM values and YSI laboratory reference measurements, with standard deviation listed as the dispersion measure. The numerical primary result is not reported in the registry record. The listed safety entry records zero affected for serious and other adverse device effects; the deaths field is null, and specific serious-event terms are not reported.

The record describes the study question and broad design, but does not report the numerical performance estimate, its uncertainty, or key analysis details.