Physical Activity Pathway for Patients With Osteoarthritis in Primary Care (OA-PCP) (R33): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Physical Activity Pathway for Patients With Osteoarthritis in Primary Care (OA-PCP) (R33) (NCT04533711), a randomized na study. The primary outcome is Change From Baseline to Month 6 in Objectively Assessed Physical Activity (Accelerometer).

2. Clinical Question

3. Trial Design

This was a randomized, single-masked, parallel-group behavioral study. The registry lists an enrollment of 240 and a completed status. The study start date was 2020-11-30, and the primary completion date was 2023-12-04. The registry record does not identify who was masked, so the masking designation cannot establish whether participants, intervention staff, assessors, or analysts were unaware of assignment.

One group received the OA-PCP intervention, a physical activity pathway intended for primary care. Its components included a process for screening for inactivity, tailored telephone counseling, connection with community programs and other resources, and follow-up counseling or referrals. The intervention description specifies an initial coaching call and five additional calls over 12 months. Participants could also receive monthly check-in emails if they agreed.

The attention control focused on understanding osteoarthritis and current information about treatment options. It used the same number of telephone calls over 12 months, with optional monthly check-in emails. Thus, the comparison was between two behavioral programs with ongoing contact, not between the pathway and no intervention. The registry record does not give further detail about how the programs were delivered, adherence to calls, or the extent to which participants used community resources.

The primary endpoint concerned accelerometer-measured moderate to vigorous physical activity at month 6. The registry also lists secondary outcomes concerning steps per day, sedentary activity, and WOMAC function and pain at month 6 and month 12. A detailed account of the allocation procedure, masking implementation, and analysis populations is not reported 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.

Overall Study

Analysis population for the primary outcome, as defined in the registry: 46 participants did not complete 6-month follow-up assessments, and 30 did not have adequate physical activity data for this measure.

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 Change From Baseline to Month 6 in Objectively Assessed Physical Activity (Accelerometer), measured over Baseline, Month 6 (Follow-up).

The primary endpoint was change from baseline to month 6 in objectively assessed physical activity, measured as minutes per week of moderate to vigorous intensity physical activity. An accelerometer was used to assess activity. The endpoint therefore focuses on recorded movement rather than relying only on participants’ recollection or a rating of activity.

Physical activity is relevant to the intervention because the OA-PCP pathway was designed to identify inactivity and support participation in activity through counseling and referrals. Measuring minutes of moderate to vigorous activity offers a quantitative way to assess whether activity changed during follow-up. An objective device measure can reduce some forms of recall error, although the registry record does not describe the device protocol, wear-time requirements, or how accelerometer data were processed.

The primary outcome was specified for baseline and month 6. The record notes that 46 participants did not complete 6-month follow-up assessments and 30 did not have adequate physical activity data for this measure. Those statements indicate that the endpoint was not available for every enrolled participant, but do not explain how missing assessments or inadequate device data were handled in the primary analysis.

The endpoint should be interpreted as a measure of activity over the stated assessment period, not as a direct measure of pain, function, or overall health. The registry lists WOMAC pain and function, steps per day, and sedentary activity among the secondary outcomes; these address different aspects of experience and activity.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: it is measured in minutes per week, and the registry identifies the summary as a mean. A mean describes the average value in a group. When groups are compared, a mean difference expresses how far apart their averages are on the measurement scale. It does not describe the spread of individual participants’ values, and it does not imply that every participant changed by the group average.

What does the confidence interval convey?

A confidence interval is a range of values calculated using a statistical procedure that reflects uncertainty in an estimate. In general, a wider interval indicates less precision than a narrower interval. The reported 95% confidence interval for the mixed-model mean difference runs from -7.68 to 24.38 minutes per week. Because this interval includes zero, the posted result is compatible with no mean difference as well as with differences in either direction. The interval also shows that the estimate is not precise enough to isolate a narrow range of possible effects.

The arm-level confidence intervals describe uncertainty around each group’s reported mean change. They are not the same as a confidence interval for the difference between groups. Looking at whether separate group intervals overlap is not a substitute for using the direct between-group analysis: the uncertainty of a contrast depends on the relationship between the estimates and on the analysis model.

What does the mixed models analysis add?

The registry identifies the sponsor’s method as mixed models analysis and labels the reported parameter a mean difference in final values. In general, mixed models can represent repeated or otherwise related observations while accounting for correlations in the data. The registry record does not give the model formula, the variables included, the covariance structure, or further details about the observations used. Those choices cannot be inferred from the method label alone.

The final-values label matters because the arm summaries are described as changes from baseline to month 6. A final-value contrast and a contrast in change are distinct descriptions of an estimand, even when both concern the same endpoint. The record does not explain the relationship between the presentation of arm changes and the sponsor’s final-values analysis, so they should not be silently treated as identical quantities.

How should the p-value be read?

In general, a p-value measures how unusual the observed data, or data more extreme, would be under a specified null model and the assumptions of the analysis. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of a difference. The reported p-value is 0.309. The registry record does not provide the full testing plan or say whether this analysis was adjusted for other outcomes or comparisons.

Why can over-dispersion matter?

In general, over-dispersion occurs when observed variation is greater than the model expects. It can make standard errors too small if the analysis does not account for the extra variability, which can in turn make confidence intervals too narrow and p-values too small. The primary outcome is continuous, and the registry does not report a specific assessment of over-dispersion or say that it was present. This general issue should not be read as a claim about the data in this trial.

What do planning illustrations represent?

Sample-size planning illustrations are hypothetical calculations, not additional trial results. The registry describes the illustrations as using a two-sided significance level of 0.05, equal allocation, a normal approximation, and fractions of the observed effect. It states that non-time-to-event results are expressed as participants per arm. Such calculations can show how a planning target depends on assumptions about the effect to detect and the desired power. They do not describe the trial’s observed power, establish the trial’s original design justification, or reveal that the registry’s investigators used those assumptions when planning the study. The trial-specific design justification is not reported in the registry record.

10. Analyses Reported by the Sponsor

The registry’s own primary comparison is the mixed models analysis, which reports a mean difference in final values of 8.35 minutes per week. Its 95% confidence interval runs from -7.68 to 24.38, and the reported p-value is 0.309. This sponsor analysis should be used as the primary inferential result rather than substituting an unadjusted comparison reconstructed from summary statistics. The record does not flag a discrepancy between the sponsor analysis and any recalculation.

The posted arm summaries report changes from baseline, while the sponsor analysis is labeled as a difference in final values. A simple unadjusted calculation from group summaries, if presented, would not reproduce all features of a mixed-model analysis. It could use a different estimand and would not account for model terms that are not reported in the registry record. For that reason, any such calculation would be a descriptive cross-check, not a replacement for the sponsor’s analysis.

The confidence interval and p-value characterize the sponsor’s analysis under its assumptions; the registry does not give enough model detail for an independent reconstruction of those assumptions. The results indicate uncertainty about the size and direction of the mean difference. They should not be recast as proof of equivalence or as a definitive conclusion about clinical importance.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 10 outcome measures and 10 analyses, including the primary endpoint and secondary outcomes involving steps per day, sedentary activity, and WOMAC function and pain at month 6 and month 12. Eight secondary outcomes are posted. The record does not describe a multiplicity adjustment, a hierarchy among secondary outcomes, or how the primary endpoint was protected from the risk of multiple testing. Without a reported plan, the probability of false-positive findings across several comparisons cannot be assessed from the outcome list alone.

Missingness is relevant to the primary result. The registry states that 46 participants did not complete 6-month follow-up assessments, and that 30 did not have adequate physical activity data for the primary measure. The wording does not specify whether these groups overlap, so no combined count should be inferred. Nor does the record state why the assessments or device data were unavailable, whether the reasons differed between groups, or whether missingness was related to participants’ activity levels.

The sponsor used mixed models analysis, but the method label alone does not establish how missing observations were handled. The record does not describe imputation, assumptions about the missing-data mechanism, sensitivity analyses, or whether participants were analyzed according to their randomized assignment. The exact analysis population is not reported in the registry record.

These omissions limit interpretation of both the primary comparison and the breadth of the secondary findings. They do not establish that the analysis was incorrect; they mean that the public record does not provide the detail needed to assess robustness to missing data or multiplicity. Interim analyses and a detailed statistical analysis plan are not reported in the registry record.

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 serious adverse events for 120 participants at risk in each group. There were 0 serious adverse events in OA-PCP and 0 in Attention Control. It also reports other, non-serious adverse events for 120 participants at risk in each group: 1 in OA-PCP and 0 in Attention Control. These are the posted event counts, not estimates of comparative risk adjusted for follow-up or other factors.

The registry records 1 death in OA-PCP and 0 in Attention Control. It does not report a serious adverse event term, and the information available does not state whether the death was related to the intervention or to the study. A death count should not be interpreted as evidence of causation. Likewise, zero reported serious events in these groups does not establish that an intervention is free of risk.

The adverse-event figures should be kept separate from the primary endpoint analysis. The registry gives different at-risk counts for the safety listings and reports missing physical activity assessments for the primary outcome. It does not explain the relationship between these populations or provide event timing, severity detail, or attribution. The figures therefore describe the safety entries recorded, but they do not support a detailed comparison of safety profiles.

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

The posted results describe a randomized comparison of a physical activity pathway with an osteoarthritis education-focused attention control. For the primary outcome, the registry reports arm-level mean changes and a sponsor mixed-model estimate of the difference in final values. The estimated difference is 8.35 minutes per week, with a 95% confidence interval from -7.68 to 24.38. That interval includes zero and spans values in both directions, indicating substantial uncertainty about the direction and size of the difference.

This result does not establish that the groups were equivalent. A confidence interval that includes zero does not show that any difference is absent; it shows that the analysis has not isolated a nonzero difference at the level of precision reported. Nor does the result establish that the pathway is clinically important or unimportant. The registry record does not provide a threshold for a clinically meaningful change in this measure.

The result also does not answer every question about physical activity or osteoarthritis. The primary measure concerns accelerometer-assessed moderate to vigorous activity at month 6. The registry lists additional outcomes for steps, sedentary activity, pain, and function, but their presence does not determine the primary result. Each outcome has its own measurement properties and missing-data considerations.

General interpretation of a randomized trial depends on how participants were assigned, followed, measured, and analyzed. The record identifies random allocation and a mixed models analysis but does not report the full analysis plan, masking details, missing-data methods, or multiplicity procedures. Those gaps limit how far the result can be generalized or independently assessed.

The appropriate reading is therefore specific: the registry reports an uncertain between-group mean difference for the stated activity outcome, alongside incomplete primary endpoint data. It neither establishes a treatment benefit nor rules one out. It also does not support medical advice or a conclusion about an individual’s care.

14. Why This Trial Matters Statistically

This trial is statistically notable because the intervention and comparator both involved repeated contact. The OA-PCP program focused on physical activity screening, counseling, and resource connections, while the attention control focused on osteoarthritis education and treatment information. The comparison therefore addresses the pathway against an active behavioral program rather than against no contact. That design makes the interpretation depend on the contrast between program content, not simply on whether participants received calls.

The primary endpoint is an objectively assessed activity measure, expressed in minutes per week. Using an accelerometer distinguishes this outcome from a self-reported rating, while also making the adequacy and completeness of device data important. The registry explicitly notes missing follow-up assessments and inadequate activity data, so measurement availability is part of the statistical context rather than a minor administrative detail.

The result also illustrates why an estimated difference should be read with its confidence interval. The point estimate alone does not convey the range of uncertainty. Here the interval extends across zero and includes differences in either direction, so the estimated mean difference is not sharply determined. A p-value by itself would not communicate this range or the practical size of values compatible with the analysis.

Finally, the registry’s labels distinguish arm-level changes from a mixed-model difference in final values. Keeping those quantities separate is essential when interpreting a trial report. The record also leaves important analysis details—such as missing-data handling and multiplicity adjustment—not reported. These are useful reminders that statistical interpretation depends both on the numerical estimate and on transparent reporting of how it was obtained.

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 record does not report detailed eligibility criteria or participant characteristics, limiting assessment of how well the enrolled population represents the broader primary care population with osteoarthritis. It also does not identify who was masked, explain how masking was implemented, or provide details about the allocation procedure beyond random assignment.

The primary endpoint has incomplete data: 46 participants did not complete 6-month follow-up assessments, and 30 did not have adequate physical activity data for the measure. Reasons for missingness, overlap between these groups, group-specific missingness, and the handling of missing values are not reported. Although the sponsor analysis used mixed models, the record does not describe the model specification or missing-data assumptions.

The mixed-model result is labeled a mean difference in final values, while the group summaries are expressed as change from baseline. The registry does not explain this difference in presentation or provide enough model details to independently reproduce the primary analysis. It also does not report a clinical-importance threshold for the endpoint.

The record lists multiple secondary outcomes but does not report a multiplicity strategy, a detailed statistical analysis plan, or interim analyses. Additional information about intervention adherence, call delivery, use of referrals, and accelerometer procedures is not reported in the registry record. The safety listings provide counts but do not give event timing or attribution. These limitations make the posted result less informative about robustness, generalizability, and implementation than a fuller report would be.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Physical Activity Pathway for Patients With Osteoarthritis in Primary Care (OA-PCP) (R33) — NCT04533711.
• Registry record last updated 2024-10-24; status last verified 2023-10.
• Results first posted 2024-10-24.
• 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

NCT04533711 is a completed, randomized, single-masked, parallel-group behavioral trial of the OA-PCP physical activity pathway compared with an osteoarthritis education-focused attention control. The registry lists an enrollment of 240, a start date of 2020-11-30, and a primary completion date of 2023-12-04. The sponsor is University of North Carolina, Chapel Hill.

The primary outcome was change from baseline to month 6 in accelerometer-measured moderate to vigorous physical activity, in minutes per week. The sponsor’s mixed models analysis reports a mean difference in final values of 8.35, with a 95% confidence interval from -7.68 to 24.38 and a reported p-value of 0.309. The interval includes zero and allows for differences in either direction.

The registry also lists secondary activity, pain, and function outcomes. It reports missing primary outcome data and safety counts, but does not describe the full statistical plan, missing-data methods, or multiplicity adjustment.