Home-base Kidney Care in Zuni Indians: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Home-base Kidney Care in Zuni Indians (NCT02915029), a randomized na study. The primary outcome is Patient Activation Measure (PAM) -13 Item Questionnaire.

2. Clinical Question

The study was designed to assess home-based care delivered by community health workers and University of New Mexico faculty in the setting of chronic kidney disease. Its stated motivation was to assess whether early intervention could delay or reduce progression toward end-stage renal disease. The primary outcome reported in the registry, however, is patient activation rather than kidney disease progression. The posted primary comparison therefore addresses change in a measure of activation in health care, not a direct comparison of end-stage renal disease outcomes. The registry also lists secondary measures including A1c, blood pressure, body mass index, and lipid measures.

3. Trial Design

The registry record describes a randomized, unmasked, factorial-model study of home-based kidney care. It lists an enrollment of 125 and a completed status. The study start is recorded as 2013-10, and primary completion as 2016-06. The sponsor is the University of New Mexico. Phase is listed as NA.

The posted primary outcome compares Education and Lifestyle Coaching with Usual Care (UC) Control Arm. For the 12-month-minus-baseline PAM outcome, the coaching arm has 50 participants in the posted summary and the usual-care arm has 48. The registry separately reports enrollment as 125; the relationship between enrollment and the outcome-specific counts is not reported in the registry record. The allocation method beyond its randomized designation, details of sequence generation, and concealment procedures are not reported in the registry record.

The coaching description includes education about diabetes and kidney disease, plus lifestyle, nutrition, and medication-adherence coaching or counseling. The usual-care description says participants were left to seek health care from their providers and received laboratory tests and surveys at 6 and 12 months of the intervention. The record does not describe masking, consistent with its designation of none. It does not explain how the factorial model was implemented or identify additional factors or factorial comparisons; those details are not reported in the registry record.

The record lists 20 outcome measures and 18 posted secondary outcomes. The primary endpoint is PAM score change at 12 months. The registry also lists secondary measures of A1c, diastolic and systolic blood pressure, body mass index, LDL and HDL cholesterol, triglycerides, and total cholesterol. The timing and analytic details beyond the posted outcome descriptions are 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

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: Members of the Zuni Pueblo, NM who have evidence of chronic kidney disease based on microalbuminuria of \>30 mg/g

6. Primary Endpoint

The registry lists the primary outcome as Patient Activation Measure (PAM) -13 Item Questionnaire, measured over 12 months follow-up minus baseline values.

The primary endpoint is the Patient Activation Measure (PAM), a 13-item questionnaire. The registry describes a total score ranging from 0-100, with higher scores reflecting higher levels of patient activation in health care. It also describes activation stages from 1 through 4, with 1 the lowest and 4 the highest activation level. The posted primary result concerns the change in total score from baseline to 12 months of follow-up, expressed as a mean.

Patient activation is used to describe a patient's level of engagement in managing health and interacting with health care. In this study, the endpoint is relevant to an intervention that includes education, coaching, and counseling. It measures a patient-reported activation construct rather than kidney function, progression to end-stage renal disease, or a clinical event. The registry’s stated purpose refers to delaying or reducing the rate of end-stage renal disease, but the posted primary endpoint is PAM change. The record does not report a primary kidney-progression endpoint in the results.

For interpretation, the direction of the score matters: a higher PAM score represents greater activation according to the registry description. A positive difference in change favoring coaching therefore indicates a larger mean increase, or a smaller mean decrease, in activation score than in usual care. It does not by itself establish whether any change is clinically important; a threshold for a meaningful PAM change is not reported in the registry record.

7. Results Posted in the Registry

• Education and Lifestyle Coaching: mean 9.10 versus -1.40 on control; difference 10.50 (95% CI 2.09 to 18.91), standardized effect d = 0.49; z-test p = 0.014.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

A1c

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Education and Lifestyle Coaching: mean -0.50 versus 0.10 on control; difference -0.60 (95% CI -1.15 to -0.05), standardized effect d = -0.43; z-test p = 0.034.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Education and Lifestyle Coaching than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Diastolic Blood Pressure

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Education and Lifestyle Coaching: mean -0.10 versus 0.20 on control; difference -0.30 (95% CI -5.81 to 5.21), standardized effect d = -0.02; z-test p = 0.915.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Education and Lifestyle Coaching and the control. The interval gives the range of effects that remain compatible with the data.

Systolic Blood Pressure

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Education and Lifestyle Coaching: mean 3.40 versus 5.20 on control; difference -1.80 (95% CI -9.33 to 5.73), standardized effect d = -0.09; z-test p = 0.639.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Education and Lifestyle Coaching and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists secondary measures spanning glycemic control, blood pressure, body size, and lipid measures. Numerical comparisons are detailed for A1c, diastolic blood pressure, and systolic blood pressure, while the record lists 18 posted secondary outcomes overall. The results described for those detailed measures do not form a uniform pattern: the A1c comparison is in a different direction from the two blood-pressure point estimates, and the blood-pressure estimates are imprecise. The registry does not report numerical details for every listed secondary measure in the information described.

These secondary measures provide context about other health indicators considered alongside the primary patient-activation outcome. They do not directly confirm or refute the PAM result, because they measure different constructs. Nor do they establish a change in kidney disease progression. The primary result concerns patient activation, while the secondary list includes metabolic and cardiovascular measures.

Unadjusted secondary comparisons carry less weight when many outcomes are examined. With multiple comparisons, some apparently notable findings can arise by chance even when no corresponding effect exists. The registry does not report whether a multiplicity adjustment or a prespecified hierarchy was used. Accordingly, secondary results are best treated as exploratory unless the analysis plan establishes otherwise. A complete interpretation also requires attention to the size and precision of each estimate, not p-values alone.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• A1c
• Diastolic Blood Pressure
• Systolic Blood Pressure
• Body Mass Index
• Low-density Lipoprotein LDL Cholesterol
• High-density Lipoprotein HDL Cholesterol
• Triglycerides
• Serum Total Cholesterol

9. Statistical Interpretation

10. Statistical Methods Explained

What does a mean change represent? The primary endpoint is a continuous measure, so the registry reports a group mean change in PAM score from baseline to 12 months. A mean describes the average observed change in the group; it does not describe every participant’s experience. The coaching arm’s mean change is 9.1 points, while the usual-care arm’s mean change is -1.4 points. The simple difference between those means is reported as 10.5 points.

What does the unadjusted comparison do? The recalculated comparison uses the posted group means and standard deviations to estimate the difference between groups without covariate adjustment. It is an unadjusted summary-based analysis, not a reconstruction of the sponsor’s full model. Its estimate is 10.5 points, with a 95% confidence interval from 2.093 to 18.91 and p = 0.014. These recalculations are useful for understanding the reported summaries, but they do not replace the analysis specified and conducted by the sponsor.

What is the standard deviation describing? The posted standard deviations are 26.0 points for coaching and 15.3 points for usual care. A standard deviation describes variation among participant outcomes around a group mean. It is not the uncertainty in the estimated group mean itself. The registry also reports standard errors for the two means as 3.677 and 2.208, respectively. Standard errors describe sampling uncertainty in estimates and are used in constructing inferential comparisons.

What does ANCOVA add? ANCOVA is a regression-based method that can compare groups while adjusting for covariates. The sponsor reports an ANCOVA net mean difference of 8.7 points, with a 95% confidence interval from 1.9 to 15.5 and p = 0.01. The specific covariates, model details, and exact interpretation of “net” are not reported in the registry record. The adjusted result should therefore be described as reported, without attributing the change from the unadjusted estimate to any particular covariate or modeling choice.

How should the p-value be read? A p-value measures how incompatible the observed data are with a specified null model, under the assumptions of the analysis. It is not the probability that the null hypothesis is true, nor a measure of the size or importance of the result. The unadjusted p-value is 0.014, and the sponsor’s reported p-value is 0.01. The registry’s planning illustration lists a two-sided significance level of 0.05; the original trial’s own significance level and analysis plan are not reported in the registry record.

What does the factorial designation mean? A factorial design can be used to study more than one intervention factor, often allowing assessment of separate effects and sometimes their interaction. That is general statistical background; it does not establish how this study’s design was implemented. Although the registry labels the model factorial, it does not report the additional factor, allocation structure, or an interaction analysis. The posted primary comparison is the coaching group versus usual care, and no further design interpretation should be assumed from the label alone.

Why can dispersion matter? When participant outcomes vary substantially, estimated group means and differences tend to be less precise unless the study has enough information to offset that variability. General statistical reasoning also cautions that unusually variable outcomes or departures from model assumptions can affect standard errors and confidence intervals. The PAM standard deviations differ across the posted arms, but the registry does not report diagnostic checks or an alternative variance model. The posted interval and p-value should be understood as results from the stated summary-based calculation or reported ANCOVA, rather than as proof that every model assumption was checked.

What is the distinction between raw and adjusted evidence? The recalculated mean difference is based on the group summaries alone. The ANCOVA estimate comes from the sponsor’s reported adjusted analysis. Adjusted and unadjusted estimates can differ because they answer the comparison using different modeling choices and information. The registry record does not provide the details needed to reproduce the ANCOVA. Because the discrepancy flag is false, there is no flagged conflict between the posted result and the recalculation; nonetheless, the recalculation remains an unadjusted analysis and should not be presented as the sponsor’s model.

11. Confidence Intervals and Precision

A confidence interval describes the range of estimates compatible with the observed data under the method’s assumptions. It communicates uncertainty around an estimated difference; it is not a range containing a known fixed proportion of individual participant outcomes. Nor does it mean that every value in the interval is equally plausible.

For the unadjusted primary comparison, the estimated mean difference is 10.5 points and the 95% confidence interval is 2.093 to 18.91. The interval is entirely positive, indicating that the summary-based estimate is more compatible with a positive mean difference than with no difference under the calculation’s assumptions. Its width also matters: the data do not identify a single precise value for the difference, and estimates across the interval remain compatible with the analysis.

The sponsor’s ANCOVA estimate is 8.7 points, with a 95% confidence interval from 1.9 to 15.5. This interval is also entirely positive and is narrower than the unadjusted interval. The two intervals come from different analyses, so their widths and endpoints should not be compared as if they were generated by an identical model. Details of the ANCOVA specification are not reported in the registry record.

Precision is distinct from whether an estimate is important. A confidence interval can describe statistical uncertainty, but the registry does not report a threshold for a clinically meaningful PAM difference. The interval therefore cannot, by itself, determine whether the estimated difference would be consequential to patients or health services. It also cannot establish whether a similar result would occur in another population or setting.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size illustrations are planning calculations based on the observed effect, not the trial’s original design assumptions. For these continuous outcomes, the figures are participants per arm, not a total event count. The registry’s stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning row considers detecting the stated fraction of the observed effect.

The 80% power column represents the number of participants per arm in a hypothetical study designed to have an 80% chance of detecting the specified effect under those assumptions, if that effect and the planning model were correct. The 90% power column makes the analogous planning illustration for a 90% chance. These are design probabilities under an assumed effect and model, not probabilities that the observed result is true.

Rows for 100%, 75%, and 50% of the observed effect illustrate how the projected sample requirement changes when the target difference is smaller. Smaller effects are harder to distinguish from random variation, so the planning calculations require more participants per arm. For the primary PAM comparison, the observed-effect row lists 66 participants per arm for 80% power and 88 for 90% power; the lower-effect rows list larger requirements.

The registry’s original sample-size justification, target effect, and design assumptions are not reported in the registry record. The posted illustration uses the observed effect for planning, which can be an unstable basis for future planning because the observed estimate itself is uncertain. This is not observed power: it is a prospective planning illustration, not a measure of the probability that the completed study had to detect its result.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 10.500; pooled standard deviation σ = 21.439.
2. n = 2 × (1.96 + 0.842)² × 21.439² / 10.500² = 65.4, rounded up to 66 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 10.5                      # observed difference in means
sigma <- 21.4394083212823                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(2915029)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 66 (80% power), 88 (90% power)
 75% of observed effect: n per arm = 117 (80% power), 156 (90% power)
 50% of observed effect: n per arm = 262 (80% power), 351 (90% power)
power.t.test: 66.4 
Simulated power at n = 66 per arm: 0.800 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Analyses Reported by the Sponsor

The sponsor reports an ANCOVA net mean difference of 8.7 points for the primary PAM outcome, with a 95% confidence interval from 1.9 to 15.5 and p = 0.01. The simple recalculation from the posted group means is an unadjusted mean difference of 10.5 points, with a 95% confidence interval from 2.093 to 18.91 and p = 0.014.

These estimates address the same group comparison but use different methods. The recalculation compares the posted summaries directly; ANCOVA is an adjusted model. The registry record does not specify the covariates or enough model detail to reproduce the sponsor’s result or explain the precise difference between estimates. Both estimates point in the same positive direction, and both confidence intervals exclude zero. The recalculation should therefore be treated as a transparent unadjusted check, not as a replacement for the sponsor’s analysis. The sponsor’s own analysis takes precedence when interpreting the trial’s reported primary analysis.

15. Multiplicity, Missing Data and Analysis Populations

The registry record lists 20 outcome measures and 18 posted secondary outcomes. Examining many outcomes creates a multiplicity issue: as the number of statistical comparisons increases, the chance of at least one apparently unusual result can also increase. This is a general statistical concern, not a claim that any specific posted result is false.

The multiplicity strategy is not reported in the registry record. It is not reported whether the study specified one primary comparison and a hierarchy for secondary outcomes, whether any adjustment was made, or whether secondary analyses were designated as exploratory. The posted unadjusted secondary p-values should therefore not be interpreted as if they necessarily account for the number of outcomes examined.

Missing-data procedures and analysis populations are also not reported in the registry record. The outcome summaries give arm-specific participant counts, but do not explain whether these are all randomized participants with available measurements, a defined analysis set, or another population. The record does not describe how missing baseline or follow-up measurements were handled, whether participants were analyzed according to randomized assignment, or whether any imputation or sensitivity analysis was used.

These omissions matter because missing outcomes can affect both the estimated group difference and its precision, especially if missingness differs between groups or relates to participants’ outcomes. That is a general concern; the registry does not report enough information to determine whether it applies in this study. The original statistical analysis plan, prespecified model details, and protocol for multiplicity and missing data are not reported in the registry record.

16. 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 serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: death (4.8%).

The adverse-event record lists serious events among groups labeled Educational Intervention and Usual Care - Control. It reports 63 at risk and 1 affected in the educational group, and 62 at risk and 3 affected in the usual-care group. Deaths are reported as 1 and 3, respectively. The record lists zero participants at risk and zero affected for other adverse events in both groups.

The registry identifies Death as the top serious adverse-event term, with 4.8% reported. These figures should be read as registry safety counts, not as proof that the intervention caused or prevented any event. The record does not provide event-level descriptions, timing, relatedness assessments, or enough detail to determine whether deaths are included among the serious events affected. It also does not report the causes of death. The reported counts do not by themselves establish comparative safety.

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

The primary result describes a greater average change in PAM score in the education and lifestyle coaching group than in usual care. The sponsor’s adjusted analysis reports a net mean difference of 8.7 points, with a 95% confidence interval from 1.9 to 15.5. The unadjusted recalculation also favors coaching. Since higher PAM scores represent higher patient activation, the results indicate a difference in the direction of greater activation in the coaching group under the reported analyses.

That finding is narrower than the study’s broader motivation. PAM is a patient-activation measure; it is not a direct measure of kidney function, progression to end-stage renal disease, heart disease, or mortality. The posted primary result therefore does not establish that the intervention delayed kidney disease progression or reduced clinical events. The registry’s stated aim and the endpoint that was reported should be kept distinct.

The result also does not establish that every participant experienced increased activation. Group means summarize outcomes and can conceal individual variation. The posted standard deviations indicate variability in the PAM changes. The registry does not report a threshold for a clinically meaningful difference, so statistical evidence of a positive group contrast does not, by itself, define its practical importance.

Finally, the record does not report enough detail to judge all aspects of the analysis, including the handling of missing data, analysis population, and multiplicity. The randomized designation is relevant to the study design, but a full assessment of how allocation and analysis were implemented requires information not reported in the registry record. The result is best understood as evidence about the posted PAM comparison, not as a general conclusion about all benefits or risks of home-based kidney care.

18. Why This Trial Matters Statistically

This trial raises statistical questions that are common in community-based clinical research: how to evaluate a patient-reported primary outcome, how to distinguish an unadjusted comparison from an adjusted analysis, and how to interpret a result alongside a broad set of secondary measures. The registry makes the distinction between mean change in PAM and the study’s wider interest in chronic kidney disease progression especially important. A statistically positive result on one construct should not be treated as evidence about a different clinical endpoint.

The posted results also illustrate why estimates and uncertainty should be read together. The sponsor’s ANCOVA estimate and the simple recalculation are not identical, but both point in a positive direction and have confidence intervals that exclude zero. The adjusted model is the sponsor’s analysis; the recalculation offers an unadjusted perspective from the group summaries. Knowing which method produced an estimate is essential to interpreting it.

Finally, the registry’s factorial designation, outcome count, and safety reporting highlight the importance of clear reporting. Readers need design details, analysis populations, missing-data procedures, and multiplicity plans to evaluate how robustly a result answers its intended question. Those details are not reported in the registry record. Their absence does not negate the posted estimates, but it limits the depth of statistical assessment possible from this record.

19. 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 primary endpoint is patient activation rather than a direct measure of kidney disease progression, even though the study’s rationale concerns delaying or reducing progression to end-stage renal disease. The registry does not report a threshold for a clinically meaningful PAM difference. Interpretation is therefore limited to the direction, magnitude, and statistical uncertainty of the activation-score comparison.

The trial is labeled randomized and factorial, but details of sequence generation, allocation concealment, implementation of the factorial structure, and any additional factor or interaction analysis are not reported in the registry record. The posted primary comparison is between coaching and usual care, and the role of any other design component cannot be assessed from the reported details.

The sponsor’s ANCOVA is reported without covariate or model specification. The analysis population, treatment of missing data, outcome completeness, and sensitivity analyses are not reported in the registry record. The relationship between the overall enrollment of 125 and the outcome-specific group counts is also not explained. These gaps limit independent reproduction and assessment of possible bias.

The record lists multiple outcomes but does not report a multiplicity strategy. Detailed numerical secondary comparisons are not available for all listed outcomes in the information described. Safety reporting gives summary counts but not event timing, causes, or relatedness. These limitations constrain interpretation of secondary findings and adverse events, and make it important not to extend the primary PAM result to unreported clinical outcomes.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: Home-base Kidney Care in Zuni Indians — NCT02915029.
• Registry record last updated 2019-12-04; status last verified 2019-12.
• Results first posted 2019-12-04.
• 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.

23. Record Summary

The registry record describes a completed randomized, unmasked, factorial-model study sponsored by the University of New Mexico, with an enrollment of 125. It compares education and lifestyle coaching with usual care for people with chronic kidney disease in the Zuni Indian community. The primary outcome is change in Patient Activation Measure score from baseline to 12 months.

The sponsor reports an ANCOVA net mean difference of 8.7 points, with a 95% confidence interval from 1.9 to 15.5 and p = 0.01. An unadjusted recalculation gives a mean difference of 10.5 points, with a 95% confidence interval from 2.093 to 18.91 and p = 0.014. Secondary measures include A1c, blood pressure, body mass index, and lipid measures. Details on the analysis population, missing data, multiplicity, and full factorial implementation are not reported in the registry record.