Study of Low Level Laser Therapy to Treat Chronic Heel Pain Arising From Plantar Fasciitis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of Low Level Laser Therapy to Treat Chronic Heel Pain Arising From Plantar Fasciitis (NCT01835743), a randomized na study. The primary outcome is Number of Participants Who Attained a Change of -30% or Greater in the VAS Score.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, triple-masked, parallel-group study comparing the Erchonia HPS Laser with a placebo laser. It lists the study as completed and records enrollment of 69. The listed start was 2012-02, and the primary completion was 2012-05. The study is listed as phase NA, which is consistent with the record being for a device rather than a drug-phase trial.

The active and placebo devices were described as matching in appearance and operation, with the placebo not emitting therapeutic light. The record does not identify which groups of people were included in the triple masking, nor does it give further details of how masking was maintained or assessed. The allocation ratio and the randomization procedure are not reported in the registry record.

The primary endpoint was a participant count: the number meeting a threshold for change in the VAS pain score from baseline to 5 weeks. The registry record also lists change in heel-pain VAS score as a secondary outcome. For this continuous outcome, group means and standard deviations are posted, as well as a comparison of group means.

Arm-level results are reported for 37 participants in the Erchonia HPS Laser group and 32 in the Placebo Laser group. These are the posted group denominators; the record does not explain whether any randomized participants were excluded from the outcome analyses or how missing outcome measurements were handled. The protocol, full eligibility criteria, and the trial's original statistical analysis plan 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.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants Who Attained a Change of -30% or Greater in the VAS Score, measured over baseline and 5 weeks.

The primary endpoint counts participants whose heel-pain VAS score changed by -30% or greater between baseline and 5 weeks. Participants rated pain during the first few steps of the day on a 0-100 mm scale, with higher scores representing more pain. The assessment at 5 weeks was 2 weeks after the end of procedure administration, according to the registry record.

The endpoint expresses improvement as a threshold-based participant count rather than as the average size of score change. The record says that a negative percentage change indicates a decrease in pain, whereas a positive change indicates worsening; it regards a change of -30% or greater as meeting the study's success criterion. The resulting count can be compared between randomized groups to assess how often participants reached that defined threshold.

A threshold outcome is straightforward to interpret as a count of participants meeting a stated criterion, but it does not show the full range of individual score changes. Participants just short of the threshold and participants with little or no improvement are grouped together as not meeting it, while the extent of change among those who meet it is not captured by the count alone. The registry record also reports a continuous VAS change outcome, which provides a complementary summary of the amount of change in scores.

7. Results Posted in the Registry

• Erchonia HPS Laser: 62.2% (23/37) versus 12.5% (4/32) on control; risk difference 49.7 percentage points (95% CI 30.3 to 69.0), risk ratio 4.97 (1.92–12.87); unadjusted two-proportion z-test p = <0.001.

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.

Change in Heel Pain Score on the Visual Analog Scale (VAS)

• 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:
  • Erchonia HPS Laser: mean -29.47 versus -5.38 on control; difference -24.09 (95% CI -33.85 to -14.33), standardized effect d = -1.13; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Erchonia HPS Laser than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The registry record lists one secondary outcome: change in heel-pain score on the VAS from baseline to 5 weeks. The posted direction of the group means aligns with the primary threshold comparison: the Erchonia HPS Laser group had a more negative mean change than the Placebo Laser group. This offers a continuous-outcome perspective on the same general symptom domain, rather than an assessment of a separate clinical domain.

The two outcomes complement one another. The primary result describes the number meeting a defined improvement threshold; the secondary result summarizes average score change. Similar direction across a threshold-based and a continuous summary can make the pattern easier to interpret, but it does not make the secondary result an independent replication. Both are recorded within the same trial and reflect the same broad outcome area and follow-up period.

Secondary findings usually carry less weight than a prespecified primary result because they may be among several analyses considered, and repeated testing can increase the chance of finding an apparently strong result by chance. The registry record does not report whether multiplicity adjustment was used, whether the secondary analysis was prespecified, or how the primary and secondary outcomes were prioritized in the analysis plan. The secondary p-value is reported without a documented adjustment in the registry record, so it should be interpreted as unadjusted rather than as a multiplicity-controlled confirmatory result.

The record lists two outcome measures and two analyses, while one secondary outcome is posted. It does not explain the relationship between the number of analyses and the number of listed outcomes. The available secondary information therefore supports a description of the recorded pattern, but not a broader claim about all possible outcomes or analyses.

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

• Change in Heel Pain Score on the Visual Analog Scale (VAS)

9. Statistical Interpretation

10. Statistical Methods Explained

The primary result is a comparison of a binary outcome: each participant either met the VAS-change threshold or did not. The group results are therefore counts of participants meeting the criterion within the posted group denominators. A difference in proportions describes the absolute gap between the groups' observed rates. It keeps the comparison on the scale of percentage-point change in the underlying proportions, although the recalculated estimate is not repeated because its posted precision exceeds the permitted display precision.

What does Fisher Exact test assess?

The sponsor reports Fisher Exact for the primary comparison. This method evaluates the evidence of association between randomized group and the binary outcome using the observed counts. It is often used for count data, particularly when the distribution of counts may not be well approximated by large-sample methods. The registry record reports the sponsor's p-value but does not provide a test statistic, a confidence interval for that analysis, or further details about the exact test implementation.

A p-value describes how unusual data at least as discrepant as those observed would be under the test's null model. It is not the probability that the groups are truly identical, and it is not a measure of the size of the difference. The sponsor's test and the recalculated comparison use the posted group counts, but their reported p-value thresholds differ. Because the record does not report a discrepancy between these analyses, the sponsor's stated result remains the primary analysis to cite.

What does the continuous-outcome comparison add?

The secondary outcome records change in VAS score as a continuous measure. The group means describe average change, while the standard deviations describe how dispersed participant scores were around each group's mean. A mean difference compares those averages, with a negative estimate indicating a more negative mean change in the Erchonia HPS Laser group under the posted direction of subtraction. The recalculated interval for the mean difference extends from -33.85 to -14.33.

The sponsor reports a two-sided t-test for this outcome. A t-test assesses whether the observed difference in group means is compatible with a null model of no mean difference, using the variability and sample information in the analysis. The posted recalculation uses summary statistics and is explicitly unadjusted. It cannot account for participant-level features or covariates not represented in the summary results. No adjusted model is reported in the registry record.

Why distinguish unadjusted recalculations from sponsor analyses?

A recalculation from group-level counts or means is useful for checking and interpreting the posted comparison using simple statistical methods. It is not a substitute for the trial's complete analysis. Group summaries cannot reveal all details that could matter in an analysis, such as the treatment of missing observations, the precise analysis population, or any prespecified adjustment. The registry record does not report those details. The recalculations are therefore best read as simple, unadjusted comparisons alongside the sponsor's reported tests.

The primary endpoint uses a threshold, while the secondary outcome summarizes continuous score change. These methods answer related but different questions. The threshold count asks how many participants passed the chosen criterion; the mean-change analysis asks how the average score changed between groups. Agreement in direction across these outcomes is informative, but neither analysis replaces the other. The secondary outcome is also subject to the limitations of secondary analyses, including the possibility of multiple outcome testing.

The registry record does not report whether an interim analysis was performed, whether the analyses were prespecified, or the statistical methods planned before the data were examined. Those omissions should not be filled by assumptions about common trial practices. The reported design features and analyses can be described, while the absent methodological details remain not reported in the registry record.

11. Confidence Intervals and Precision

Precision concerns how much uncertainty surrounds an estimated group difference. A confidence interval gives a range of values compatible with the observed data under the interval method's assumptions. It is not a guarantee that the true value lies within the particular interval, and its interpretation depends on the method and confidence level used. The confidence level for the recalculated intervals is not reported in the registry record.

For the continuous VAS comparison, the recalculated mean difference is -24.09, with an interval from -33.85 to -14.33. The interval is entirely on the negative side of zero, consistent with the observed lower mean change in the Erchonia HPS Laser group. Its endpoints still allow a range of possible magnitudes; the point estimate alone should not be treated as exact. This interval reflects sampling uncertainty under the recalculation, not uncertainty about every source of bias or measurement error.

The primary binary comparison also has a recalculated interval, but its endpoints are reported with more than three decimal places and are not reproduced. The registry record does not report a confidence interval for the sponsor's Fisher Exact analysis. The sponsor's p-value and the recalculated interval answer related but distinct questions: the p-value summarizes evidence against a null model, while an interval communicates a range of effect sizes compatible with the data and method.

Interval width depends on the observed data and the method used. A narrower interval generally conveys greater statistical precision, while a wider interval indicates more uncertainty about the magnitude. Precision is not the same as freedom from bias, and a statistically precise estimate can still be affected by missing data, outcome measurement, or analysis choices. The registry record does not provide enough information to evaluate all of those factors.

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 planning figures are participants per arm, not total events. They are illustrations based on the observed effect in this trial, rather than the original design assumptions. The record'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 scenario uses the stated fraction of the observed effect as the effect to detect. The trial's own original design assumptions are not reported in the registry record.

For the primary binary outcome, the posted illustrations list participants per arm for 80% power and participants per arm for 90% power at 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. The corresponding 80% power figures are 14, 24, and 47 participants per arm; the 90% power figures are 18, 31, and 62 participants per arm. For the continuous VAS outcome, the corresponding figures are 13, 22, and 49 participants per arm for 80% power, and 17, 30, and 66 participants per arm for 90% power.

In general terms, 80% power means that a study designed under the stated assumptions would have an 80% chance of detecting the specified effect at the stated significance level if that effect were the true effect. The 90% column applies the same idea with a higher target probability of detection. These are design-planning concepts, not guarantees about a particular future study. Smaller effects require more participants to detect under otherwise unchanged assumptions, which is why the planning figures rise as the effect fraction falls.

These values are not observed power. They are planning illustrations computed from the observed effects, and the observed effects may not represent the effects that a future study would encounter. They do not establish that the completed trial was planned using these assumptions, nor do they replace a design calculation based on an independently justified target effect.

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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.125; treatment proportion p₁ = 0.622; average p̄ = 0.373.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6840 = 1.3407.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5870 = 0.4940.
4. n = (1.3407 + 0.4940)² / (0.4966)² = 13.6, rounded up to 14 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
p0 <- 0.125                          # control proportion
p1 <- 0.621621621621622                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(1835743)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 14 (80% power), 18 (90% power)
 75% of observed effect: n per arm = 24 (80% power), 31 (90% power)
 50% of observed effect: n per arm = 47 (80% power), 62 (90% power)
power.prop.test: 13.6 
Simulated power at n = 14 per arm: 0.822 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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's reported primary analysis is Fisher Exact, with a p-value recorded below the threshold displayed in the registry record. The simple unadjusted recalculation from the posted counts gives p <0.001. The sponsor's own analysis takes precedence over a recalculation from summary statistics. The discrepancy indicator is false, so the registry record does not flag a conflict requiring a separate reconciliation.

The sponsor's report does not include an effect estimate or confidence interval for the primary test. The recalculation supplies a simple comparison based on the posted counts, but it should not be mistaken for the sponsor's full analysis or for an adjusted analysis. The registry record does not say whether the sponsor's test used any additional features beyond the method named.

For the continuous secondary outcome, the sponsor reports a two-sided t-test with p < 0.001, while the simple unadjusted recalculation gives p <0.001. These are related analyses of the posted group means, but the sponsor's analysis is the reported trial analysis. The recalculated mean difference and interval are useful for describing magnitude and uncertainty, subject to the limits of using summary statistics. Neither p-value should be read as the probability that a treatment effect is true.

15. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when several outcomes, time points, subgroups, or statistical tests are examined. Without an adjustment or a prespecified testing strategy, the chance of at least one small p-value can rise as more comparisons are made. This general concern does not show that a particular reported result is false; it means the analysis plan and the number of tests matter when assessing confirmatory evidence.

The registry record lists a primary outcome and a secondary VAS outcome, but it does not report a multiplicity adjustment or a hierarchical testing procedure. It also does not report whether additional outcomes, subgroup analyses, or exploratory tests were conducted. The number of outcome measures and analyses recorded in the registry does not, by itself, establish the complete set of analyses performed. The strength of evidence from the secondary analysis should therefore be read with that uncertainty in mind.

Missing-data handling is also not reported in the registry record. The posted denominators identify the group sizes used for the reported outcomes, but the record does not state whether all participants had outcome data, how missing scores were handled, or whether any imputation was used. It does not describe reasons for missingness or whether missingness differed by group. Without those details, the effect of missing outcome data on the estimates cannot be assessed from the registry summary alone.

The analysis population is not defined in the registry record. It is not stated whether results follow an intention-to-treat approach, a per-protocol approach, or another population definition. The record also does not report protocol deviations or exclusions from analysis. These are material details because the population analyzed can affect how a randomized comparison is interpreted.

The original statistical analysis plan, interim analyses, and the protocol's sample-size justification are not reported in the registry record. No assumptions about those matters can be inferred from the posted p-values or planning illustrations. The absence of these details does not negate the recorded results, but it limits assessment of whether the analyses were fully prespecified and how robustly they addressed multiple testing and incomplete data.

16. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry record reports zero serious adverse events among 37 participants at risk in the Erchonia HPS Laser group and zero among 32 participants at risk in the Placebo Laser group. It also reports zero other adverse events in each group, with the same respective at-risk counts. These figures mean that no events in those categories were recorded in the posted results for the reported groups.

Zero reported events should not be taken as proof that an event cannot occur. The figures describe what was recorded in this trial, and the ability to detect uncommon events depends on the amount and duration of observation. The adverse-event reporting timeframe is not reported in the registry record. The record lists no serious adverse-event terms. Death counts are not reported in the registry record.

These data are descriptive and do not establish comparative safety beyond the events and observation captured in the record. They should be interpreted alongside the trial's size, follow-up, and reporting limitations, rather than as a complete characterization of potential harms.

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

The posted results show that more participants in the Erchonia HPS Laser group than in the Placebo Laser group met the primary VAS-change threshold at 5 weeks. The continuous VAS summary also shows a more negative mean change in the active-device group. The sponsor's reported tests and the simple recalculations indicate statistical evidence of between-group differences under their respective analyses.

Those findings describe outcomes in this randomized study; they do not establish that the result will be the same in other populations, settings, or follow-up periods. The record does not report longer-term outcomes. It also does not provide enough information to assess missing data, analysis population, baseline comparability, or whether multiplicity was addressed. These limitations affect how broadly and confidently the estimates can be applied.

The primary endpoint is a trial-defined threshold on a self-rated pain scale. Meeting that threshold does not capture the full range of individual changes, and the group average does not imply that every participant changed by the average amount. The continuous and threshold outcomes provide different summaries of pain-score change and should be read as such.

The results do not establish the mechanism behind any observed difference, nor do the registry summaries by themselves establish the balance of benefits and harms over time. No serious or other adverse events were recorded in the posted group summaries, but that is not equivalent to proving that no adverse events can occur. The record supports a careful description of the observed outcomes and their statistical uncertainty, not medical advice or a universal conclusion about treatment.

18. Why This Trial Matters Statistically

This trial provides an example of how a randomized, placebo-controlled comparison can be reported using both a binary primary outcome and a continuous secondary outcome. The primary endpoint turns score change into a threshold-based count, while the secondary outcome preserves information about average change. Considering both makes clear that outcome definition affects the statistical question being asked.

The posted results also illustrate why effect estimates and uncertainty matter alongside p-values. A p-value can indicate evidence against a null model, but it does not communicate the magnitude or range of plausible effects. For the continuous outcome, the recalculated mean difference and interval add information about magnitude and precision. For the primary count outcome, the group counts offer a direct description of how often the criterion was met.

The distinction between a sponsor-reported analysis and an unadjusted recalculation is useful for critical reading. A calculation based on summary data can help contextualize the result, but it does not recover details absent from a registry summary or replace the analysis reported by the sponsor. The record's unreported analysis-population, missing-data, and multiplicity details underscore the value of transparent protocols and statistical plans.

Finally, the planning illustrations show how assumptions about the effect to detect shape sample-size requirements. They are separate from the trial's original design justification, which is not reported in the registry record. Treating such calculations as planning aids rather than evidence of observed power helps keep design concepts distinct from results.

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.

Several limitations specific to this trial can be identified from the registry record. The primary outcome is based on a percentage-change threshold in a self-rated VAS score. The record defines the direction of change and the success threshold, but does not provide information on the validation of this threshold for this study or on how participants were instructed to complete the scale beyond the stated rating prompt.

Follow-up for the reported primary and secondary outcomes is at baseline and 5 weeks, with the 5-week assessment occurring 2 weeks after procedure administration ended. Longer-term outcome results are not reported in the registry record, so the posted results do not describe persistence of change over a longer period. The record also does not report details about treatment administration beyond the device descriptions.

The trial is described as triple-masked, but the record does not specify who was masked or provide information about the success of masking. It gives no detailed account of random sequence generation, allocation concealment, baseline group characteristics, or eligibility criteria. These omissions constrain evaluation of how the randomized design was implemented and how closely the groups were comparable at baseline.

For the outcome analyses, missing-data procedures, analysis-population definitions, protocol deviations, and adjustment for multiplicity are not reported in the registry record. It is also not clear whether the continuous outcome was prespecified as secondary or whether other analyses were conducted. These uncertainties should remain explicit rather than being resolved by assumptions about typical trial practice.

The posted adverse-event summary records no serious or other adverse events in either group, but does not report the adverse-event observation period or death counts. Therefore, the safety summary is limited to those recorded categories and figures. The record does not provide details sufficient to assess uncommon or delayed events.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: Study of Low Level Laser Therapy to Treat Chronic Heel Pain Arising From Plantar Fasciitis — NCT01835743.
• Registry record last updated 2014-06-03; status last verified 2014-05.
• Results first posted 2014-06-03.
• 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

NCT01835743 is a completed randomized, triple-masked, parallel-group, placebo-controlled device study of the Erchonia HPS Laser for chronic heel pain arising from plantar fasciitis. The registry record lists enrollment of 69 and study dates from 2012-02 to primary completion in 2012-05. The comparator was a placebo laser described as matching the active device in appearance and operation without therapeutic light.

The primary outcome counted participants attaining a change of -30% or greater in heel-pain VAS score between baseline and 5 weeks. The posted counts were 23 of 37 in the Erchonia HPS Laser group and 4 of 32 in the placebo group. The secondary outcome was change in VAS score; its posted group means favored a more negative change in the active-device group. Sponsor analyses reported Fisher Exact for the primary result and a two-sided t-test for the secondary result.

Important details, including the original statistical plan, analysis population, missing-data handling, multiplicity approach, and longer-term outcomes, are not reported in the registry record. The results are therefore best read as the recorded comparisons at the stated follow-up, with those reporting limitations in view.