Preventive Care of Chronic Cervical Pain and Disabilities: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Preventive Care of Chronic Cervical Pain and Disabilities (NCT00566930), a randomized na study. The primary outcome is Neck Pain.

2. Clinical Question

3. Trial Design

The registry identifies this as a randomized, double-masked, factorial trial and records its status as completed. Enrollment is listed as 117. The registry identifies Université du Québec à Trois-Rivières as the sponsor. The recorded start is 2007-10 and primary completion is 2008-09. The phase is listed as not applicable.

Three arms have posted primary outcome data: control, spinal manipulation, and spinal manipulation and exercises. The number of participants recorded for the primary outcome differs across those arms. The arm descriptions do not provide further detail about the control condition, masking procedures, or how the factorial design was structured. Those details are not reported in the registry record.

The study summary describes a planned comparison of control, spinal manipulation, and an individualized home exercise program, and separately states a hypothesis about spinal manipulation combined with a home exercise program. The posted arm descriptions list spinal manipulation and spinal manipulation with exercises, but not a home-exercise-only arm. The relationship between the summary’s planned groups and the final posted arm structure is not explained in the registry record.

The primary outcome timeframe is listed as up to 10 months. The study summary refers to a hypothesis concerning outcomes over a 1 year period, so the registry does not fully reconcile that description with the primary outcome timeframe. The record’s design label does not by itself establish which treatment effects or interactions were intended to be estimated. The protocol, treatment allocation details, and 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.

Before assignment: 117 participants were initially recruited. Following the initial clinical assessment, 98 met all inclusion criteria and were assigned to one of the three groups. 19 participants were excluded because they did not met all inclusion criteria (most common reason was that their neck pain could not be diagnosed as a common non specific neck pain).

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 Neck Pain, measured over Up to 10 months.

The primary endpoint is neck pain measured in centimeters using a visual analog scale. The scale runs from 0 to 10 cm, with 0 defined as no neck pain and 10 as extreme neck pain. The registry reports a mean and standard deviation for each arm, with the outcome timeframe listed as up to 10 months.

A continuous pain score retains information about the degree of pain rather than reducing the result to categories such as pain present or absent. A mean describes the average score in an arm; a standard deviation describes how spread out scores are around that average. The mean difference compares the average score in an intervention arm with the control average. A negative estimate in these comparisons means the intervention arm’s posted average is lower than control’s average, given the order used in the registry contrast.

Pain is relevant to the study’s stated aim of reducing chronic cervical pain. The study summary also mentions functional capacity, quality of life, and general health, but the primary endpoint posted in the registry is the pain scale. Measures of fear avoidance belief, quality of life, and range of motion appear among the listed secondary outcomes. Their results are not included in the primary outcome figures described in this analysis. A threshold for a clinically important change in the pain score is not reported in the registry record, so the size of a mean difference cannot be judged against such a threshold from this record alone.

7. Results Posted in the Registry

• Spinal Manipulation: mean 3.30 versus 3.80 on control; difference -0.50 (95% CI -1.39 to 0.39), standardized effect d = -0.28; z-test p = 0.269.
• Spinal Manipulation and Exercises: mean 3.40 versus 3.80 on control; difference -0.40 (95% CI -1.30 to 0.50), standardized effect d = -0.22; z-test p = 0.385.

8. Statistical Interpretation

9. Statistical Methods Explained

Mean differences compare average scores between arms. In the posted contrasts, control is the reference group, and the estimate is the intervention-arm mean minus the control mean. A negative value therefore indicates a lower average score in the intervention arm. Because the outcome is measured in centimeters on the pain scale, the mean difference is also expressed in centimeters. This makes the contrast interpretable in the original measurement units.

What does a confidence interval convey?

A confidence interval expresses uncertainty around an estimated contrast. In general, it is a range generated by a statistical method that reflects both the estimate and its precision. A narrower interval indicates greater precision under the assumptions of that method; a wider interval indicates greater uncertainty. It is not a guarantee that the true effect lies within that particular interval, and it does not measure the probability that a treatment works.

For both posted comparisons, the confidence interval includes zero. Zero represents no mean difference between the groups in the scale’s units. The intervals also extend to negative and positive values, so the posted summaries leave uncertainty about the direction and size of the underlying contrast. The p-values are 0.269 for spinal manipulation versus control and 0.385 for spinal manipulation and exercises versus control. They are unadjusted values and should be interpreted alongside the estimates and intervals, not as measures of effect size or clinical importance.

Why do standard deviations matter?

The standard deviation describes variability among individual scores within an arm. It is not the uncertainty of the arm mean itself. Mean uncertainty also depends on the number of observations and the method used to analyze them. When individual scores vary substantially, a mean contrast may be estimated less precisely, all else being equal. The posted arm standard deviations are 1.9 for control, 1.7 for spinal manipulation, and 1.7 for spinal manipulation and exercises.

In general, over-dispersion means that observed variability is greater than a model assumes. If a statistical model underestimates variability, its standard errors may be too small and its intervals too narrow. The primary measure is continuous, and the record reports standard deviations rather than event counts. The registry does not report a model assessing over-dispersion, nor does it provide an analysis plan that would clarify model assumptions.

What do the recalculated comparisons represent?

The contrasts use posted means and standard deviations to give simple, unadjusted comparisons with control. They do not account for factors beyond those summary statistics, and they do not establish that the investigators used the same calculations in their own analysis. The registry record lists zero analyses. The recorded discrepancy indicator is false, but this does not supply an investigator analysis or additional modeling details. These recalculations should be understood as a way to examine the posted summaries, rather than as evidence of a prespecified trial analysis.

The record labels the trial factorial, which generally refers to a design that evaluates more than one intervention factor and may permit assessment of their separate and combined effects. That general label alone is not enough to identify the factors, contrasts, or model used. The posted arm descriptions show control, spinal manipulation, and spinal manipulation and exercises, while the registry does not list a home-exercise-only arm among the posted arms. No factorial interaction estimate or factor-specific analysis is reported.

What information is missing for a fuller analysis?

The registry does not report the original statistical plan, the original sample-size justification, interim analyses, analysis populations, missing-data methods, or adjustment for multiple comparisons. It also does not explain whether outcome observations were selected from one visit or combined over time. For a longitudinal outcome, the choice of visit or repeated-measures model can affect the estimate and its uncertainty. Without those details, the posted summaries cannot establish how the trial handled repeated measurements or missing observations.

General statistical interpretation also depends on how randomization, masking, and outcome measurement were implemented. The registry records randomization and double masking, but does not say which people were masked or how masking was maintained. These details are not reported in the registry record. The posted results therefore support a limited description of the observed arm means and unadjusted contrasts, not a complete reconstruction of the trial’s statistical methods.

10. Confidence Intervals and Precision

The mean difference for spinal manipulation versus control is -0.5 cm. Its 95% confidence interval runs from -1.387 to 0.387. The mean difference for spinal manipulation and exercises versus control is -0.4 cm, with a 95% confidence interval from -1.303 to 0.503. Both intervals include zero and span values on both sides of it. The point estimates alone would give an incomplete account of how uncertain these comparisons are.

In general, a confidence interval combines an estimated effect with its sampling uncertainty, conditional on the method and assumptions used. The intervals are broad enough to include no difference, as well as negative or positive mean differences. Their width cautions against treating the observed estimates as precise determinations of the size or direction of a population difference. The posted p-values, 0.269 and 0.385, are consistent with this uncertainty, but p-values do not communicate the range of plausible values as directly as confidence intervals.

The arm means and standard deviations provide useful descriptive context, but the registry does not report a sponsor analysis, analysis model, or missing-data procedure alongside them. The contrasts are unadjusted recalculations based on the posted summaries. Their intervals should be interpreted in that limited context. The record also does not report a threshold for a clinically important difference, so statistical uncertainty cannot be translated into a judgment about whether any particular value would matter to participants.

Precision is not the same as validity or clinical importance. An estimate can be precise but not clinically important, or imprecise while still leaving open potentially meaningful differences. These posted intervals show that the estimated comparisons are uncertain; they do not resolve the study’s broader question about preventive care.

11. 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 for 80% power and participants per arm for 90% power. They are based on a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each scenario uses the stated fraction of the observed effect: 100%, 75%, or 50%. The figures are planning illustrations based on the observed effect, not the trial’s own original design assumptions. The original design assumptions are not reported in the registry record.

The 80% power column gives the planned number of participants in each arm under the listed assumptions for a design intended to have an 80% chance of detecting the specified effect if that effect is real and the assumptions hold. The 90% power column gives the corresponding per-arm planning number for a design intended to have a 90% chance. These are design targets, not guarantees about a future study’s result.

The planning numbers differ by contrast and by the fraction of the observed effect being targeted. For spinal manipulation versus control, the figures range from 202 participants per arm for 100% of the observed effect at 80% power to 1,080 participants per arm for 50% of the observed effect at 90% power. For spinal manipulation and exercises versus control, they range from 317 participants per arm for 100% of the observed effect at 80% power to 1,695 participants per arm for 50% of the observed effect at 90% power. The intermediate scenarios are also listed for each comparison.

Smaller effects require more participants to detect under the same general planning approach, which is why the scenarios targeting a smaller fraction of the observed effect have larger planning figures. These values are not observed power for this completed trial; they are prospective illustrations derived from the observed estimates. The registry does not report that these assumptions were used to plan the trial.

12. 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 = -0.500; pooled standard deviation σ = 1.792.
2. n = 2 × (1.96 + 0.842)² × 1.792² / -0.500² = 201.6, rounded up to 202 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 <- -0.5                      # observed difference in means
sigma <- 1.79164728671689                     # 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(566930)
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 = 202 (80% power), 270 (90% power)
 75% of observed effect: n per arm = 359 (80% power), 480 (90% power)
 50% of observed effect: n per arm = 807 (80% power), 1,080 (90% power)
power.t.test: 202.5 
Simulated power at n = 202 per arm: 0.804 (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.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists more than one comparison of an intervention arm with control, along with secondary outcomes. When several outcomes or comparisons are examined, the chance of obtaining an apparently unusual result by chance can increase. General approaches to multiplicity include defining a primary comparison in advance, adjusting inference across a family of tests, or clearly identifying analyses as exploratory. The original multiplicity strategy is not reported in the registry record.

The posted p-values are unadjusted. No adjustment for multiple comparisons is reported, and the record lists zero analyses. The registry does not identify whether these contrasts were prespecified, whether other comparisons were planned, or how secondary outcomes were handled. The listed secondary outcomes are fear avoidance belief, quality of life, and range of motion, but results for those outcomes are not presented with the primary outcome data.

The record does not report missing-data methods or analysis populations. It is therefore unclear from the registry whether the reported arm summaries include all randomized participants, only participants with observed outcomes, or another defined group. The enrollment field records 117, while the outcome summaries have arm-specific counts. These figures should not be treated as a complete account of follow-up or missingness: the registry does not explain the relationship between enrollment and the outcome-specific records.

The record also does not report whether participants were analyzed according to randomized assignment, whether exclusions occurred, or how any incomplete repeated measurements were addressed. The outcome timeframe extends up to 10 months, but the precise visit or summary used for the posted means is not specified. These gaps limit assessment of potential bias and reproducibility. They do not establish that missing data or multiplicity affected the results; rather, the methods needed to evaluate those possibilities are not reported in the registry record.

14. 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 records zero serious adverse events in the control group, zero in the spinal manipulation group, and zero in the spinal manipulation and exercises group. The corresponding numbers at risk are 29, 36, and 33. The record does not list serious adverse event terms. Deaths are not reported in the registry record.

These entries describe what was recorded for the groups and event category in the registry. Zero reported events is not proof that an intervention is free of risk. Interpretation depends on how events were defined, collected, and followed, and on the completeness of reporting. Those methods are not reported in the registry record.

The registry also records zero other adverse events in each of the three groups, with the same group-specific numbers at risk. The record does not provide event descriptions or additional safety detail. These results should be read as registry reporting for the recorded categories, not as a comprehensive assessment of safety or as medical advice.

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

The posted primary outcome results show lower mean neck-pain scores in both intervention arms than in control: 3.3 cm for spinal manipulation and 3.4 cm for spinal manipulation and exercises, compared with 3.8 cm for control. The corresponding unadjusted mean differences are -0.5 cm and -0.4 cm. Both confidence intervals include zero, and the estimates remain uncertain. The registry data therefore describe observed differences but do not establish a clear distinction from no mean difference.

This does not settle whether either approach changes pain, whether a difference would be important to participants, or whether the combined intervention is better than spinal manipulation alone. The registry does not provide a threshold for clinical importance, a direct comparison between the two active arms, or a factorial analysis separating intervention components. The study summary also describes goals concerning function, quality of life, and general health, but the posted primary outcome is neck pain and the other results are not reported alongside these comparisons.

The trial’s completed status and randomized, double-masked labels are part of the registry record, but they do not fill gaps in the posted analysis methods. The record does not describe masking procedures, missing-data handling, the analysis population, or the original statistical plan. The estimates are unadjusted recalculations from arm summaries, rather than a reported sponsor analysis. They should not be read as definitive evidence of benefit or lack of benefit.

The appropriate conclusion is limited: the registry reports arm-level pain averages and uncertain unadjusted comparisons for the stated timeframe. It does not provide enough information to answer every question in the study summary or to judge the clinical importance of the observed contrasts. No treatment recommendation follows from these registry results.

16. Why This Trial Matters Statistically

This trial is statistically interesting because its registry label is factorial while its posted arm descriptions show control, spinal manipulation, and spinal manipulation with exercises. A factorial design can be used to study separate intervention components and their combination, but the label alone does not reveal which effects were estimated. The posted summaries do not include a home-exercise-only arm or a factorial interaction analysis, so the combined treatment’s component effects cannot be separated from these results.

The continuous pain outcome makes the results interpretable in the scale’s original centimeters. The arm means show the observed average scores, while standard deviations convey variability among scores. Mean differences, confidence intervals, and unadjusted p-values add a comparison and an indication of uncertainty. Here, both intervals include zero, illustrating why effect estimates should be considered together with their uncertainty rather than interpreted from arm means alone.

The record also illustrates the distinction between a trial’s own analysis and a simple recalculation from posted summaries. The comparisons described are unadjusted recalculations, while the registry lists zero analyses and does not provide the original analysis plan. The planning illustrations likewise depend on stated assumptions and the observed effects; they do not reveal how the completed trial was originally planned.

Finally, the record exposes the limits of registry reporting for longitudinal and safety interpretation. The primary timeframe is listed as up to 10 months, but the precise visit or summary behind the means is not specified. Adverse-event counts are recorded, but definitions and collection methods are not. These points matter because a numerical result is most useful when readers can understand how it was obtained, which participants it represents, and what uncertainty remains.

17. 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 does not explain the control condition, treatment schedules, adherence, or the details of the individualized home exercise program. It labels the trial factorial but does not describe the factors or explain how the posted arms correspond to the design. The study summary refers to a home exercise program and a combined approach, whereas the posted arm descriptions list control, spinal manipulation, and spinal manipulation with exercises. The record does not reconcile these descriptions.

The outcome timeframe is stated as up to 10 months, while the study summary refers to a hypothesis over a 1 year period. The registry does not identify the exact visit, averaging method, or repeated-measures analysis used for the posted outcome summaries. It also does not report an analysis population, missing-data handling, adjustment for multiple comparisons, or the original statistical plan.

The recorded enrollment is 117, while the primary outcome arm records have their own participant counts. The registry does not explain the relationship between enrollment and those outcome counts, so these numbers cannot establish follow-up completeness. The brief summary’s planned recruitment description is also not reconciled with the enrollment field.

The posted comparisons are unadjusted recalculations. No sponsor analysis is included, and no clinical-importance threshold is reported. Secondary outcome results are not reported with the primary contrasts. Safety entries record no events in the posted categories, but event definitions and ascertainment methods are absent. These limitations constrain what can be concluded from the registry record; they do not show that any particular bias or reporting problem occurred.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Preventive Care of Chronic Cervical Pain and Disabilities — NCT00566930.
• Registry record last updated 2012-09-28; status last verified 2012-09.
• Results first posted 2012-09-14.
• 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.

21. Record Summary

The registry record describes a completed, randomized, double-masked factorial trial sponsored by Université du Québec à Trois-Rivières. Enrollment is listed as 117. The condition is Neck Pain, and the primary outcome is mean neck pain on a 0 to 10 cm visual analog scale, with a timeframe of up to 10 months.

Posted outcome arms are control, spinal manipulation, and spinal manipulation and exercises. Their mean scores are 3.8, 3.3, and 3.4 cm, respectively. The unadjusted mean differences versus control are -0.5 cm and -0.4 cm; both confidence intervals include zero. The registry lists zero analyses and does not report the original statistical plan, missing-data methods, or a multiplicity strategy.

Serious and other adverse events are recorded as zero in each arm. The record does not report deaths or event terms. The results support a description of posted arm summaries and uncertain unadjusted comparisons, but do not resolve the broader questions about prevention, functional outcomes, or the separate effects of the combined intervention.