OPAM-IA: Using Digital Activity Trackers to Improve Physical Activity in Inflammatory Arthritis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for OPAM-IA: Using Digital Activity Trackers to Improve Physical Activity in Inflammatory Arthritis (NCT02554474), a randomized na study. The primary outcome is Daily Time in Moderate/Vigorous Physical Activity.

2. Clinical Question

3. Trial Design

OPAM-IA is recorded as a randomized, crossover behavioral trial and is listed as completed. The registry reports 118 enrolled participants and identifies 59 participants randomized to each group. The study concerns inflammatory arthritis; rheumatoid arthritis and systemic lupus erythematosus are named in the condition and study descriptions. The intervention combines a wireless activity tracker, an online application, group education and telephone counselling by a physiotherapist.

The immediate group received the intervention, while the delay group was assigned the same intervention with a 9-week delay. The primary endpoint was assessed at baseline and at weeks 9, 18 and 27. Those repeated time points are relevant to understanding the crossover design: group assignment determines when participants receive the intervention, while measurement continues across the stated follow-up schedule. Further detail on the sequence of intervention and measurement periods is not reported in the registry record.

The registry describes the allocation as randomized and the model as crossover. An analysis note also identifies the trial as cluster-randomized and cautions that a simple individual-level re-analysis would be misleading. The unit of cluster assignment and details of the clustering structure are not reported in the registry record. That caveat matters because observations from people assigned within the same cluster may not be statistically independent; an analysis that treats them as independent could give misleading uncertainty estimates.

The record lists nine outcome measures and nine analyses. The primary outcome is daily time in moderate/vigorous physical activity; secondary outcomes include sedentary activity, fatigue, pain, depressive symptoms, health-management measures and activity-related habits. The statistical method used for the primary sponsor-reported estimate is not specified in the registry record.

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.

Before assignment: After completing baseline measures at home, participants were randomized to the Immediate or Delay Group in 1:1 allocation ratio.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: 59 participants were randomized into each group. Week 9: Immediate Group - 3 withdrew;1 with missing data. Delay Group - 2 withdrew Week 18: Immediate Group - 3 additional participants withdrew; 2 with missing data. Delay Group - 1 additional participant withdrew. Week 27: Immediate Group - 1 additional participants withdrew, Delay Group - no additional participant withdrew; 6 with missing data.

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 Daily Time in Moderate/Vigorous Physical Activity, measured over Baseline, 9 weeks, 18 weeks, 27 weeks.

The primary endpoint is daily time spent in moderate/vigorous physical activity, expressed in minutes. A SenseWear Mini sensor measured activity over a 7-day period. The endpoint is the mean daily time in activity bouts: a bout is defined as at least 10 consecutive minutes at a level of at least 3 METs, with an allowance for interruptions of up to two minutes below the threshold.

Using a sensor provides an objective measure of movement rather than relying solely on a participant’s recall of activity. The endpoint focuses on sustained activity at or above the stated intensity threshold, rather than all movement accumulated during the day. Repeated measurement at baseline and weeks 9, 18 and 27 permits assessment of change over the trial’s follow-up periods.

In general, a mean is useful for describing the average amount of a continuous outcome in a group, while also potentially concealing variation among individuals. The registry defines the primary measure using a mean and standard deviation. It does not report the distribution of individual activity measurements or explain how the endpoint was handled when sensor data were missing.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary result is described as an adjusted difference in mean change. That wording indicates a comparison of changes in the average endpoint rather than a simple comparison of final group means. The reported estimate is 9.4 minutes, and the uncertainty interval is a 95% confidence interval from -0.5 to 19.3 minutes. The record does not report the statistical model, adjustment variables, standard error, or p-value used to produce the sponsor’s result.

What does an adjusted difference in mean change represent?

In general, a change score describes how an outcome differs from an earlier measurement for the same participant or group. A difference in mean change then compares those changes between groups. Adjustment means that the reported comparison accounts for one or more additional factors in the analysis, but the specific factors and their role cannot be determined unless they are described. They are not reported in the registry record for this result. Because the estimate is adjusted, it should not be treated as a raw subtraction of group averages.

The endpoint is continuous, measured in minutes per day, and summarized as a mean with a standard deviation. In general, the mean expresses an average level, while the standard deviation describes how spread out individual observations are around that average. The registry does not include the group means or standard deviations for the primary result in the reported analysis, so an independent calculation of the adjusted difference cannot be reconstructed from those summaries.

How should the confidence interval be read?

In general, a confidence interval describes uncertainty in an estimate under the assumptions and methods of the analysis. The 95% interval ranges from -0.5 to 19.3 minutes. Since that range crosses zero, the data and method do not exclude a zero difference in mean change. The interval also includes values above zero, so it does not establish that the underlying difference is exactly zero. The interval’s interpretation depends on the analysis being appropriate for the design, including its handling of clustering and repeated measurements. Those details are not reported in the registry record.

The confidence interval is not a range containing 95% of individual participants’ activity changes. It concerns the estimated contrast, not the spread of individual outcomes. It also does not state the probability that a particular value in the interval is the true effect. These are general properties of confidence intervals; the exact statistical procedure used for this sponsor-reported interval is not specified.

Why does the design affect the analysis?

The registry identifies a crossover design, with an immediate group and a group receiving the same intervention after a 9-week delay. Measurements are listed at baseline and weeks 9, 18 and 27. In general, crossover studies require attention to the timing of treatment and measurements, because outcomes may reflect both the assigned sequence and the period in which they are recorded. The registry does not report whether the analysis modeled period effects, sequence effects or possible carryover from an earlier intervention period.

The analysis note additionally describes the trial as cluster-randomized and warns that a simple individual-level re-analysis would be misleading. In general, people assigned within a shared cluster may have more similar outcomes than people in different clusters. This dependence is called within-cluster correlation. Ignoring it can make uncertainty appear smaller than it should be. The record does not specify the cluster unit, the number of clusters, or the sponsor’s method for accounting for clustering, so those features cannot be independently evaluated.

What can be inferred from the reported analysis?

The reported estimate and interval describe the sponsor’s adjusted comparison as recorded. They do not identify the adjustment variables, the analysis population, or the treatment of missing measurements. No p-value is reported. A significance conclusion based on an unreported p-value should not be substituted for interpretation of the interval. In general, statistical evidence and clinical importance are different questions: an estimate can be uncertain, and whether a particular magnitude matters clinically requires a relevant threshold or context. Such a threshold is not reported in the registry record.

The registry lists nine outcome measures and nine analyses. In general, evaluating several outcomes can raise a multiplicity question: when many comparisons are made, the chance of at least one apparently unusual result can increase. The registry does not report a multiplicity adjustment or analysis hierarchy. This does not establish that no adjustment was used; it means that the approach is not reported in the registry record.

The sample-size calculations described as planning illustrations use a two-sided significance level of 0.05, equal allocation, a normal approximation and an effect defined as a stated fraction of the observed effect. They are not the trial’s original design calculations and should not be read as observed power. The registry record does not report a sample-size justification for the trial. In general, a planning calculation describes the sample size associated with specified assumptions; it does not reveal the probability that the completed trial produced a particular result.

10. Analyses Reported by the Sponsor

The sponsor’s own primary analysis reports an adjusted difference in mean change of 9.4 minutes, with a 95% confidence interval from -0.5 to 19.3 minutes. The record’s analysis note says the trial is cluster-randomized and cautions that a simple individual-level re-analysis would be misleading. For that reason, the reported sponsor estimate is the relevant result to interpret; the record does not present an independent recalculation for comparison.

The sponsor’s adjustment method, covariates, handling of clustering and analysis population are not reported in the registry record. The registry also does not state which group is subtracted from which in the reported contrast. Consequently, the estimate can be described numerically, but its direction cannot be assigned to the immediate or delayed group from the record alone.

The confidence interval spans zero, so it does not exclude no difference in mean change. No p-value is reported. Without a recalculated estimate or further information about the sponsor’s model, there is no basis in the record to claim that a separate calculation confirms or contradicts the sponsor’s analysis.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists nine outcome measures and nine analyses. The primary endpoint is daily time in moderate/vigorous physical activity; listed secondary measures include sedentary activity, fatigue, pain, depressive symptoms, health-management measures and activity-related habits. The registry does not report a prespecified testing hierarchy, a multiplicity adjustment, or which outcomes were treated as confirmatory. The absence of those details means the chance of selective emphasis across several outcomes cannot be assessed from the registry record.

Some attrition information is reported for the primary outcome. At week 9, the immediate group had 3 withdrawals and 1 participant with missing data; the delay group had 2 withdrawals. At week 18, the immediate group had 3 additional withdrawals and 2 participants with missing data; the delay group had 1 additional withdrawal. The week 27 description is incomplete, so the remaining details are not reported in the registry record. These figures distinguish withdrawals from missing data as described by the registry; they do not explain why data were unavailable.

The record does not state whether the primary analysis included all randomized participants, only participants with available measurements, or another analysis population. It also does not describe imputation, likelihood-based handling of incomplete repeated measurements, or sensitivity analyses for missing data. In general, missingness can affect an estimate if the availability of measurements is related to participants’ outcomes or changes over time. The extent and direction of any such effect cannot be established from the information reported.

Because the analysis note warns against simple individual-level re-analysis of this cluster-randomized trial, the missing-data and multiplicity limitations should be considered alongside the design caveat. The record does not provide enough detail to evaluate whether clustering, repeated measurements, multiple outcomes and attrition were addressed jointly in the sponsor’s analysis.

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 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports no serious adverse events in either group: the immediate group has 0 serious events among 59 at risk, and the delay group also has 0 among 59 at risk. Deaths are reported as 0 in both groups. These are the recorded serious-event and death figures for the groups, not evidence that no unrecorded events occurred.

Other adverse events are reported for 13 participants in the immediate group and 10 in the delay group, with 59 at risk in each group. The registry does not provide descriptions of these events in the registry record reported for this analysis, so their type, severity and relationship to the intervention cannot be assessed. No top serious-event terms are listed.

In general, safety counts should be interpreted in light of how events were defined, collected and classified, as well as the duration of observation. Those details are not reported in the registry record. The figures therefore describe what the record reports but do not establish comparative safety or rule out uncommon harms.

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

The primary result is an adjusted difference in mean change in daily bouted moderate/vigorous physical activity. The estimate is 9.4 minutes, with a 95% confidence interval from -0.5 to 19.3 minutes. This interval includes zero, so the result does not rule out no difference between the compared changes. It also spans positive values, indicating substantial uncertainty about the size of the contrast. Because the contrast order is not specified, the numerical direction cannot be assigned to the immediate or delayed group.

The result does not establish whether the observed magnitude is important to participants. A clinically meaningful threshold is not reported in the registry record. Nor does the estimate, by itself, establish a change in sedentary activity, fatigue, pain, mood, health-management behavior or other secondary outcomes. Those measures are listed, but their results are not reported among the registry entries for this analysis.

The estimate is sponsor-reported and adjusted. Details about the adjustment, clustering, analysis population and missing-data handling are not reported. The record warns that a simple individual-level re-analysis would be misleading because the design is described as cluster-randomized. These omissions limit independent evaluation of how the estimate and its uncertainty were obtained.

In general, a randomized comparison can help assess differences between assigned groups, but conclusions depend on the design, analysis and completeness of follow-up. Here, the crossover structure, delayed intervention and repeated measurement schedule are relevant to interpretation. The registry does not specify how period effects or possible carryover were handled. The reported result should therefore be read as the sponsor’s adjusted comparison, rather than as a definitive account of every time-specific outcome or all possible effects of the intervention.

The trial record identifies a combined behavioral program involving an activity tracker, an application, group education and physiotherapist counselling. The primary estimate cannot isolate the contribution of any one component. It also cannot establish how results would apply to people or settings not described in the registry record. No medical advice or treatment recommendation follows from this statistical result.

14. Why This Trial Matters Statistically

This trial raises several statistical issues that often arise when behavior is measured repeatedly over time. The primary endpoint is sensor-recorded activity rather than a single end-of-study report, and the registry gives four assessment occasions: baseline and weeks 9, 18 and 27. A crossover design with a delayed intervention makes the timing and sequence of those measurements central to the interpretation of a change comparison.

The registry’s note that the trial is cluster-randomized is particularly important. In general, randomization by groups rather than by individuals changes the appropriate unit of analysis and the calculation of uncertainty. A simple analysis treating every participant as independent may understate uncertainty when participants within a cluster are more alike. The registry explicitly cautions against that kind of re-analysis, while not reporting the cluster structure or the sponsor’s method for addressing it.

The reported result also illustrates why an estimate should be read together with its confidence interval. The 9.4-minute adjusted difference is not a fully precise description of the contrast: the 95% confidence interval runs from -0.5 to 19.3 minutes and includes zero. This makes the uncertainty visible without requiring a binary interpretation based on a p-value, which is not reported.

Finally, multiple outcomes and incomplete follow-up affect how much can be concluded from a registry result. Nine outcomes and nine analyses are listed, but a multiplicity strategy is not reported. Some withdrawals and missing measurements are described, while later follow-up information is incomplete. These are not reasons to discard the estimate; they are reasons to keep its scope clear and to avoid treating one adjusted result as a complete account of the trial.

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 registry provides only one sponsor-reported primary contrast, without a p-value or a stated ordering of the groups in the contrast. The estimate therefore cannot be assigned to the immediate or delayed group from the record alone. The adjustment variables and statistical model are also not reported, preventing a detailed assessment of how the adjusted difference was derived.

The trial is described as a crossover study, and an analysis note calls it cluster-randomized. The unit of cluster assignment, the cluster structure and the method used to account for clustering are not reported in the registry record. The record also does not state how period effects or possible carryover were considered. These missing details matter for interpreting repeated measurements in a delayed-intervention design.

Follow-up information is incomplete. The record reports some withdrawals and missing data through week 18, but the week 27 population description is cut off. The analysis population and missing-data method are not reported. Without those details, it is not possible to evaluate how attrition relates to the reported adjusted result.

The registry lists nine outcome measures and nine analyses but does not report a multiplicity strategy or a hierarchy of outcomes. Results for the listed secondary outcomes are not included in the registry record reported for this analysis. Participant eligibility details, baseline characteristics, the sample-size justification and additional information about event collection are also not reported in the registry record. These limitations constrain both statistical appraisal and the scope of conclusions that can be drawn from the primary estimate.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: OPAM-IA: Using Digital Activity Trackers to Improve Physical Activity in Inflammatory Arthritis — NCT02554474.
• Registry record last updated 2024-01-30; status last verified 2024-01.
• Results first posted 2021-06-04.
• 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

OPAM-IA is a completed randomized crossover behavioral trial of an activity-tracking and counselling program for people with inflammatory arthritis, including rheumatoid arthritis and systemic lupus erythematosus. The intervention combined a Fitbit Flex paired with FitViz, group education and telephone counselling by a physiotherapist; the delay group received the same intervention after a 9-week delay. The primary endpoint was mean daily bouted moderate/vigorous physical activity measured with a SenseWear Mini sensor at baseline and weeks 9, 18 and 27.

The sponsor-reported adjusted difference in mean change was 9.4 minutes, with a 95% confidence interval from -0.5 to 19.3 minutes. The interval includes zero, and the registry does not report a p-value or identify the contrast order. The record lists 118 enrolled participants, warns against a simple individual-level re-analysis because of cluster randomization, and does not report the sponsor’s statistical model, missing-data method or multiplicity strategy.