Investigating Racial Differences in Diet Benefits for Knee Osteoarthritis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Investigating Racial Differences in Diet Benefits for Knee Osteoarthritis (NCT04343716), a non-randomized na study. The primary outcome is WOMAC Pain Change.

2. Clinical Question

3. Trial Design

The registry describes a completed, nonrandomized, parallel study sponsored by the University of Alabama at Birmingham. Enrollment was 19. The study concerned knee osteoarthritis and a behavioral intervention, a low-carbohydrate diet. The listed groups are White women and Black women, both described as aged 65-75 with knee osteoarthritis. The registry summary says the investigators intended to recruit 20 women, with 10 in each racial group; that planned enrollment differs from the recorded total enrollment.

The diet intervention lasted 6 weeks. According to the registry summary, participants first completed a week of diet and pain self-report, then received meals and snacks weekly after consultation with study personnel. Testing was scheduled every 3 weeks during the intervention. The summary describes quality-of-life, depression, experienced-pain, and evoked-pain assessments, with blood drawn at baseline and at the conclusion of the diet for oxidative stress assays. The listed primary outcome timeframe is baseline (week 0) and immediately after the intervention (6 weeks).

Allocation is recorded as nonrandomized and masking as none. These features matter when interpreting group differences: assignment was not randomized, and participants or study personnel were not masked according to the registry. A parallel design means the groups are considered alongside one another rather than as successive periods for the same participants, but the registry does not report the detailed assignment procedure or the analysis that accounted for group differences.

The registry record does not report a protocol-level sample-size justification, a detailed statistical analysis plan, or interim analyses. It also does not report whether every participant completed the intervention or each scheduled assessment. The record's completion status is completed, but that status alone does not establish that every planned measurement was available for analysis.

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 WOMAC Pain Change, measured over Baseline (week 0), immediately after the intervention (6 weeks).

The primary endpoint is change in WOMAC pain score from baseline to week 6. WOMAC is the Western Ontario and McMaster Osteoarthritis Index. The pain score sums questions 1-5 and ranges from 0-20; higher scores reflect more severe pain. The registry defines the change score as the baseline score minus the week 6 score and notes that numbers closer to zero indicate no change.

This measure provides a defined way to describe pain at two time points and the difference between them. Because the subtraction is baseline minus week 6, a positive change corresponds to a lower score at week 6 than at baseline, while a value near zero corresponds to little change on this scale. That is a description of the score's direction, not a judgment about clinical importance. The registry record does not report a threshold for a clinically meaningful change.

Change in a continuous score can retain more information about the size and direction of individual measurements than reducing the outcome to a binary category. However, interpretation depends on the distribution of observed scores, the completeness of measurements, and the analysis method. The registry identifies the reported parameter as a mean and the dispersion as a standard error, but it does not provide the group means, standard errors, or a comparison of change between groups. The primary endpoint's observed results are therefore not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a continuous primary outcome, WOMAC pain change, and says the parameter is a mean with standard error as the dispersion measure. It does not report the statistical test, model, covariates, or method used to compare groups. The explanations below describe general statistical concepts relevant to this kind of outcome; they should not be read as a description of methods actually used in the study.

What does a mean change represent?

For a continuous score, a mean summarizes the average value across the participants included in an analysis. A mean change would summarize the average of the baseline-to-week-6 score changes, using the registry's specified subtraction of baseline minus week 6. It is a group-level description and does not show how much individual participants differed from one another. A mean can be affected by unusually high or low observations, especially when the analysis group is small.

The registry lists the standard error as the dispersion measure. In general, a standard error describes the precision of an estimated mean, rather than the spread of individual participant scores. It is not interchangeable with a standard deviation. A standard deviation describes variability among observations; a standard error describes uncertainty in an estimated mean under the assumptions of the method used. Since the registry does not report numerical standard errors, the precision of the means cannot be evaluated from this record.

How should a confidence interval be understood?

In general, a confidence interval gives a range of values compatible with an estimate under the method's assumptions. For a between-group difference, it can convey both the estimated direction and the uncertainty around the size of that difference. A narrow interval indicates more precision than a wide interval, while an interval that includes no difference may indicate that the data are compatible with no difference as well as with some differences in either direction. A confidence interval does not make a nonrandomized comparison causal, and it does not resolve bias from confounding or missing measurements.

No confidence interval or between-group estimate is reported in the registry record. Therefore, the precision of the primary comparison cannot be described. A p-value, even if available, would not by itself convey the size or practical importance of an effect; it would need to be considered alongside the estimate, its uncertainty, the design, and the quality of the data.

What does nonrandomized allocation imply?

In general, random allocation helps balance measured and unmeasured participant characteristics across groups on average. With nonrandomized allocation, groups may differ before the intervention begins. If those characteristics are related to the outcome, a later difference in scores may reflect those baseline differences as well as any response to the intervention. Statistical adjustment can sometimes address measured differences, but it cannot guarantee removal of unmeasured confounding. The registry record does not report an adjustment method or enough participant-level information to assess baseline balance.

The racial groups in this study are not randomized intervention and control groups. The registry describes the low-carbohydrate diet intervention and two racial groups of women; it does not describe a separate comparison group that did not receive the intervention. A comparison of changes between the groups therefore addresses whether the changes differed between those enrolled groups, not the causal effect of the diet versus no diet.

How should the planning calculations be read?

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 the two arms, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect, and that the calculations are planning illustrations rather than the trial's own design. No calculated participant counts are reported in this record. Those illustrations should not be confused with the actual enrollment or with an observed result.

In general, sample-size calculations estimate how many observations may be needed to detect a specified effect under stated assumptions. They are conditional on the assumed effect, variability, allocation, and statistical method. A calculation made after observing an effect is a planning exercise; it is not evidence that the completed study had a particular probability of detecting an effect. The registry record does not report a protocol sample-size justification or an observed-power analysis. Sample sizes from planning illustrations are not observed power.

The stated equal-allocation assumption is also an assumption for the planning calculation, not evidence that the recorded groups were equal in size. The registry summary's intended recruitment and the total recorded enrollment are distinct from the actual number contributing outcome data. The record does not report group-specific primary-outcome analysis counts.

What remains unknown about the analysis?

The registry record does not report whether the primary analysis used a comparison of change scores, a model of follow-up scores adjusted for baseline, or another approach. These approaches can differ in assumptions and in how they use repeated measurements. It also does not report how repeated assessments, missing values, influential observations, or departures from model assumptions were handled. There is no basis in this record to attribute a particular statistical technique to the investigators.

Because the primary outcome is continuous, general analyses may rely on assumptions about the distribution of the outcome or model residuals. If variability differs substantially between groups, methods that assume equal variability may not describe uncertainty well. If observations are more variable than a model expects, standard errors can be too small; this issue is often described generally as over-dispersion. Whether either issue arose in this study is not reported in the registry record. Assessing them would require data and methods information not included in the record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 12 outcome measures and names secondary outcomes including WOMAC Physical Function, BPI Pain Interference Change, TS Pain Intensity Change, RCS Pain Intensity Change, and PHQ-9 Depression Change. Examining multiple outcomes can raise a multiplicity issue: when many hypotheses are tested, the chance of at least one apparently unusual result can increase. General approaches include defining a primary outcome in advance, adjusting for multiple tests, or treating secondary findings as exploratory. The registry record does not report whether any multiplicity strategy was specified or applied.

The record identifies WOMAC Pain Change as the primary outcome, but it does not report the analysis population or the number of participants with usable primary-outcome data. Recorded enrollment was 19; that number does not establish how many participants had measurements at both baseline and week 6. The missing-data rules, reasons for missing measurements, and any imputation or sensitivity analyses are not reported in the registry record.

The registry records zero analyses. This means the record does not contain reported analysis results; it does not show how data were handled in any analysis outside the registry. The statistical model, covariate adjustment, analysis population, and any per-protocol or intention-to-treat approach are not reported in the registry record. Without those details, it is not possible to determine precisely which participants contributed to each estimate or how robust an estimate would be to missing data or alternative analytical choices.

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's adverse-event figures list White Women with 1 participant at risk and Black Women with 15 participants at risk. For both groups, the listed number with a serious adverse event is 0, the number with another adverse event is 0, and deaths are 0. These are the recorded counts in the registry, not estimates of comparative risk.

The at-risk counts shown for these adverse-event entries do not add up to the total recorded enrollment of 19. The registry record does not explain that discrepancy or state whether the entries cover every enrolled participant. The figures should therefore be read as the adverse-event counts recorded for the listed groups, without assuming they are a complete safety summary for all participants.

Zero recorded events means that no events of those categories are listed in these entries. It does not establish that an event is impossible, nor does it quantify the precision of a safety estimate. The registry does not report further detail about event definitions, collection procedures, duration of safety monitoring, or whether any events were assessed as related to the diet. No serious adverse-event terms are listed. These record details do not support a broader comparison of safety between groups.

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

The study addresses an important statistical question: whether changes in knee osteoarthritis pain during a low-carbohydrate diet differ between Black and White women. It specifies a primary pain measure, a baseline-to-week-6 timeframe, and the direction used to calculate change. The record also identifies the nonrandomized parallel design and records completed status. These details describe what the study set out to assess.

They do not provide the primary outcome result. No group means, mean changes, between-group estimate, standard error, confidence interval, or p-value are reported in the registry record. Consequently, the size, direction, and precision of any group difference cannot be stated. The record does not establish whether the average pain score changed, whether one group changed more than the other, or how consistently individual participants' scores changed.

Even if a group difference were reported, this design would not by itself show that race caused a difference in response or that the diet caused a change. Allocation was nonrandomized, the record does not describe a no-diet control group, and it does not report adjustment for potential confounders. Group differences could be associated with other characteristics or circumstances. The recorded racial categories should be understood as the groups used in this study, not as randomized exposures.

The study's intended enrollment was 20, while recorded enrollment was 19. This small total limits how much information the study can provide, especially for comparing groups and estimating uncertainty. The analysis sample may also be smaller, but the registry record does not report how many participants contributed complete primary-outcome data.

The defensible conclusion from the registry record is therefore about the study's question and design, not an outcome benefit or lack of benefit. The posted information does not permit a numerical assessment of the primary endpoint or a precise comparison between groups.

13. Why This Trial Matters Statistically

Statistically, the study focuses on a question about effect variation across groups rather than only on an average change in the full enrolled population. A mean change in each group and a direct estimate of the difference between those changes would answer different descriptive questions. The latter is the quantity most directly aligned with asking whether change differed between the groups. The registry record does not report either set of estimates, so the intended comparison cannot be evaluated numerically.

The design also makes clear why the distinction between association and causation matters. The groups were not formed by random allocation to different treatments, and no separate untreated comparison group is described. A group difference in change could be influenced by baseline differences or other factors. Statistical methods can describe or adjust for measured variables, but a model cannot automatically eliminate all sources of confounding. The registry record does not identify which, if any, adjustment methods were used.

The recorded enrollment of 19, compared with the planned 20 described in the summary, underscores the importance of reporting analysis counts and uncertainty. A total enrollment figure is not enough to determine the number of complete outcome records or the precision of a group comparison. Clear reporting of group-specific counts, outcome estimates, and confidence intervals would be needed to judge how informative the observed data are.

The study also names several secondary outcomes. Their results could provide broader descriptive context, but interpreting multiple outcomes requires clarity about which analyses were planned and whether any multiplicity strategy was used. Those details are not reported in the registry record. Without them, secondary findings, if reported elsewhere, would need to be interpreted with attention to their exploratory status and uncertainty.

These statistical considerations matter because the study's racial-comparison objective is not answered by enrollment, completion status, or a list of outcome measures alone. Transparent estimates and methods would be necessary to distinguish a group-level pattern from a precise, robust, and causally interpretable finding.

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.

Several limitations are specific to the design and record. First, allocation was nonrandomized and masking was recorded as none. The groups may therefore differ in ways that affect pain scores or their change, and the registry does not report the assignment procedure or methods for addressing baseline differences. The design does not support treating the groups as randomized treatment arms.

Second, the registry describes a diet intervention but does not identify a separate no-diet or usual-care comparison group. A before-and-after change during the 6-week intervention cannot, on its own, distinguish an intervention effect from changes over time or other influences. A comparison between racial groups does not supply that missing control.

Third, the record describes an intended enrollment of 20 and a recorded enrollment of 19. The actual numbers in each group contributing to the primary analysis, and the completeness of baseline and week 6 measurements, are not reported in the registry record. This makes it difficult to assess the information available for the planned comparison.

Fourth, the primary result and analysis details are absent. The record does not report group estimates, uncertainty, the statistical test or model, covariate adjustment, missing-data handling, or a multiplicity approach. The listed adverse-event at-risk counts also do not account for the total recorded enrollment, and the record does not explain that discrepancy.

Finally, the described population is limited to women aged 65-75 with knee osteoarthritis, and the intervention period was 6 weeks. The registry record does not establish how findings would apply to people outside that described population or timeframe. These design and reporting limitations constrain interpretation independently of the direction any unreported outcome might have taken.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Investigating Racial Differences in Diet Benefits for Knee Osteoarthritis — NCT04343716.
• Registry record last updated 2026-08-13; status last verified 2026-08.
• Results first posted 2025-01-09.
• 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

NCT04343716, titled “Investigating Racial Differences in Diet Benefits for Knee Osteoarthritis,” is recorded as completed and sponsored by the University of Alabama at Birmingham. The study concerns knee osteoarthritis and a behavioral low-carbohydrate diet intervention. Its design is listed as nonrandomized, parallel, and unmasked, with recorded enrollment of 19.

The primary outcome is WOMAC Pain Change from baseline (week 0) to immediately after the 6-week intervention. The score ranges from 0-20, with higher scores indicating more severe pain; change is defined as baseline minus week 6. The summary describes intended recruitment of 20 women aged 65-75, with equal representation across racial groups.

The registry record does not report primary-outcome estimates, statistical analysis results, missing-data procedures, or a detailed analysis plan. It lists 12 outcome measures and records zero analyses. Thus, the record describes the study design and question, but does not provide a numerical answer to the primary comparison.