Physical Activity and Leisure-time Study (PALS): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Physical Activity and Leisure-time Study (PALS) (NCT01342471), a randomized phase 1 study. The primary outcome is Physical Activity (Steps/Day).

2. Clinical Question

The study addresses whether a familiar sedentary activity can be paired with movement, and compares that approach with a scheduled walking program. The primary endpoint is physical activity measured as steps per day. Secondary outcomes include total energy intake, TV-related energy intake, weight and TV viewing time. These measures capture different aspects of activity and behavior; they should not be treated as interchangeable outcomes.

The registry record identifies the trial as randomized and single-masked, with a parallel-group model. It does not describe who was masked, how allocation was generated or concealed, or which groups were eligible to participate. Those details are not reported in the registry record, so the question can be described from the listed interventions and outcomes, but the exact implementation and target population cannot be characterized further.

3. Trial Design

The Physical Activity and Leisure-time Study (PALS), registered as NCT01342471, is recorded as a randomized, single-masked, parallel-group trial. Its listed phase is PHASE1. The registry record gives enrollment as 58 and identifies the University of Tennessee as sponsor. The study is marked completed, with a start date of 2010-09 and primary completion in 2011-06.

The two behavioral interventions were TV commercial stepping and a 30-minute walking program. In the stepping arm, participants were instructed to move during commercial breaks while watching at least 90 minutes of television programming on at least 5 days per week. In the walking arm, participants were instructed to walk briskly for at least 30 minutes per day, at least 5 days per week, using bouts of at least 10 minutes. The registry record permits either one longer walking bout or multiple qualifying bouts.

The primary outcome is the change in pedometer-measured steps per day between 0 and 6 months. The posted arm summaries list 29 participants in each group. The registry record does not report the randomization procedure, allocation concealment, the identity of the masked parties, adherence to the assigned activities, or whether the outcome assessors were masked. The description of the stepping arm is incomplete in the registry record, so further details of that intervention should not be inferred.

The record lists four secondary outcomes: total energy intake, TV-related energy intake, weight and TV viewing time. Results are posted for total energy intake, TV-related energy intake and weight; a numerical result for TV viewing time is not reported in the registry record. The record does not include reported statistical analyses. The comparisons discussed in the posted results are unadjusted recalculations from the arm summaries, rather than analyses described by the trial investigators.

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 Physical Activity (Steps/Day), measured over 0 and 6 months.

The primary endpoint is physical activity measured as steps per day by pedometer. The registry record defines the outcome as the change in steps per day between 0 and 6 months. A step count offers a quantitative way to represent ambulatory activity, and comparing mean changes between the randomized arms asks whether the average change differed between the two assigned activity approaches.

The posted arm values are 2,956 steps/day for the 30-minute walking group and 2,994 steps/day for the TV commercial stepping group. The estimated mean difference, expressed as TV commercial stepping minus 30-minute walking, is 38 steps/day. The 95% confidence interval is -361.9 to 437.9 steps/day. Because this interval spans zero, the posted summaries are compatible with a range of possible differences in either direction. The unadjusted p-value is 0.852.

These values describe a between-group contrast in mean change, not the number of steps taken during every day of the study or a measure of whether an individual met a guideline. The registry record does not report the pedometer protocol, the number of days measured, how missing measurements were handled, or whether the posted arm values represent all randomized participants. Those measurement and analysis details are not reported in the registry record.

7. Results Posted in the Registry

• TV Commercial Stepping: mean 2,994 versus 2,956 on control; difference 38.00 (95% CI -361.94 to 437.94), standardized effect d = 0.05; z-test p = 0.852.

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.

Total Energy Intake

• 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:
  • TV Commercial Stepping: mean -347.90 versus -354.20 on control; difference 6.30 (95% CI -89.70 to 102.30), standardized effect d = 0.03; z-test p = 0.898.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between TV Commercial Stepping and the control. The interval gives the range of effects that remain compatible with the data.

TV Related Energy Intake

• 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:
  • TV Commercial Stepping: mean -282.60 versus -516.60 on control; difference 234.00 (95% CI 164.97 to 303.03), standardized effect d = 1.74; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for TV Commercial Stepping than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Weight

• 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:
  • TV Commercial Stepping: mean -0.70 versus -0.40 on control; difference -0.30 (95% CI -0.37 to -0.23), standardized effect d = -2.12; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for TV Commercial Stepping than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary outcomes cover distinct aspects of behavior and health: total energy intake, TV-related energy intake, weight and TV viewing time. The posted numerical results are for the first three. A numerical result for TV viewing time is not reported in the registry record. The results do not form one uniform pattern: some recalculated contrasts are more clearly separated from zero than the primary steps/day contrast, while the total energy intake estimate is comparatively uncertain.

These outcomes can complement the primary endpoint by describing whether differences in activity are accompanied by differences in related behaviors or measurements. They do not directly validate the primary result, because energy intake, weight and viewing time are different constructs from pedometer-measured steps. Nor does a result on one secondary endpoint establish a corresponding effect on the others.

The secondary comparisons are unadjusted recalculations from posted group summaries, and the registry record lists no reported analyses. It also does not report a multiplicity plan, such as which secondary outcomes were confirmatory or how repeated statistical testing was handled. When multiple outcomes are examined, some apparently notable results can arise by chance even when each individual calculation uses a conventional threshold. This general concern makes secondary findings less definitive without a prespecified testing strategy.

The appropriate reading is therefore an overall pattern rather than a collection of isolated claims: the primary endpoint has substantial uncertainty, while some secondary contrasts appear more distinct in the posted unadjusted calculations. The record does not establish whether those secondary outcomes were prioritized, whether their analyses were planned in advance, or whether all measured outcomes were reported. They are useful for describing the posted dataset, but carry less evidential weight than a prespecified, fully reported primary analysis.

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

• Total Energy Intake
• TV Related Energy Intake
• Weight
• TV Viewing Time

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous, and the registry identifies its parameter as a mean with standard deviation. A mean describes the average outcome in a group; a standard deviation describes how variable individual measurements are around that average. For this trial, the outcome is change in pedometer-measured steps per day from 0 to 6 months. The posted group values are means of that change, not baseline step counts.

What does the mean difference represent?

The comparison is expressed as TV commercial stepping minus 30-minute walking. A positive estimate means the posted mean change is higher in the stepping arm; a negative estimate means it is lower. The primary estimate is 38 steps/day. This is a contrast between group averages. It does not say that every participant changed by that amount, and it does not describe the distribution of individual responses.

The recalculated comparison is a simple unadjusted comparison of the posted summary statistics. It does not include a covariate adjustment, repeated-measures model or other adjustment unless such information appears in the registry record; no reported analysis is listed there. The posted results also do not identify an investigator-reported test for the primary comparison. Accordingly, the recalculated estimate and p-value should be understood as descriptive statistical reconstructions from the posted group summaries, not as a substitute for a trial analysis that is absent from the record.

How should the confidence interval be read?

A confidence interval describes the range of effect estimates reasonably compatible with the data under the statistical method used. It communicates uncertainty about the estimated mean difference, rather than a range containing a stated proportion of individual participants. For the primary contrast, the 95% confidence interval is -361.9 to 437.9 steps/day. Its inclusion of zero means that no difference is among the values compatible with the interval. The interval also includes differences in either direction, illustrating why the point estimate should not be interpreted in isolation.

The interval is calculated from the posted summary data using the unadjusted comparison. It does not incorporate details that are not reported, such as any clustering, baseline adjustment, or handling of missing outcomes. The registry record does not report those methods, so the interval cannot be assumed to reflect an analysis that used them.

What does the p-value add?

The unadjusted p-value for the primary contrast is 0.852. A p-value measures how compatible the observed result is with a statistical model in which the true mean difference is zero. It is not the probability that the null hypothesis is true, nor does it measure the probability that the result is due to chance. Interpreting it alongside the estimate and confidence interval is more informative than using a threshold alone.

For the secondary TV-related energy intake and weight contrasts, the recalculated unadjusted p-values are <0.001. The total energy intake comparison has an unadjusted p-value of 0.898. Since multiple outcomes are listed and the registry record does not report a multiplicity plan, these p-values should not be read as confirmatory findings. The secondary analyses are also not reported analyses in the registry record.

Why can variation affect precision?

Standard deviations describe variation within arms. Greater variation makes it harder to estimate a group mean precisely from a given amount of information, because observed participants may differ more from one another. The posted standard deviations for steps/day are 604.0 in the walking arm and 918.0 in the stepping arm. The larger spread in the stepping arm contributes to uncertainty in the comparison; however, the confidence interval reflects the combined uncertainty in the two group means and the estimated contrast.

Over-dispersion is a general concern when the variability in data is greater than a statistical model assumes. If present and not accounted for, uncertainty estimates can be too small. The registry record does not report a model-based analysis or an over-dispersion assessment. The posted outcome is continuous, so a count-data model should not be presumed from the fact that steps are counted.

The posted recalculations use the posted group means, standard deviations and group sizes as summarized in the registry record. They are unadjusted and should be interpreted within that limitation. No discrepancy between the posted comparison and the recalculated result is flagged in the registry record. Information about missing data, analysis populations, protocol deviations and the original statistical plan is not reported in the registry record.

11. Confidence Intervals and Precision

Precision is reflected by the confidence interval around an estimated contrast. For the primary outcome, the estimated difference is 38 steps/day, and its 95% confidence interval runs from -361.9 to 437.9 steps/day. This interval is wide enough to include a difference favoring either group, as well as zero. The estimate therefore gives a direction and central value, but the interval shows that the magnitude and direction are not pinned down closely.

The interval is not a prediction of the range of changes for individual participants. It describes uncertainty about the mean difference between arms under the unadjusted calculation. It should be read together with the group summaries and the limits of the available reporting, including the absence of a reported analysis plan and missing-data methods.

For the secondary comparisons, the TV-related energy intake interval is 165.0 to 303.0 kcals/day, while the total energy intake interval is -89.7 to 102.3 kcals/day. The weight comparison has an estimated difference of -0.3 kg; the posted interval bounds have more than 3 decimal places and are not reproduced. The secondary estimates have different units and should not be compared by their raw magnitudes. Their uncertainty and the multiplicity of outcomes also matter when judging how much weight to place on them.

Confidence intervals are not guarantees that a true effect lies within the stated limits. They are statistical summaries conditional on the method and data used. Because no investigator-reported analysis is listed, the intervals presented for the recalculated contrasts should be viewed as unadjusted estimates based on the posted summaries.

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 for the continuous outcomes in this trial. The record's assumption statement distinguishes these from time-to-event calculations, which would report total events; no time-to-event outcome is listed. The original trial's own sample-size assumptions are not reported in the registry record.

The planning illustration uses a two-sided significance level of 0.05, equal allocation between the two arms and a normal approximation. It takes the observed effect as a reference and considers the stated fraction of that effect as the effect to detect. For the primary steps/day comparison, planning for 100% of the observed effect gives 6,564 participants per arm for 80% power and 8,787 participants per arm for 90% power. The rows for smaller fractions of the observed effect require larger per-arm sample sizes.

In plain language, 80% power means that, if the assumed effect and planning model were correct, a study of the indicated size would have an 80% chance of detecting an effect at the specified significance level. The 90% power column describes a higher target chance under the same assumptions. These are design-planning quantities, not a probability that the observed finding is true or a measure of the result's importance.

Smaller effects are harder to distinguish from random variation, so detecting them requires more participants under otherwise unchanged assumptions. The displayed curves and figures should be read as illustrations based on the observed effect, not as a reconstruction of the trial's original design. This is not observed power.

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 = 38.000; pooled standard deviation σ = 777.026.
2. n = 2 × (1.96 + 0.842)² × 777.026² / 38.000² = 6,563.6, rounded up to 6,564 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 <- 38                      # observed difference in means
sigma <- 777.026383078464                     # 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(1342471)
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 = 6,564 (80% power), 8,787 (90% power)
 75% of observed effect: n per arm = 11,669 (80% power), 15,621 (90% power)
 50% of observed effect: n per arm = 26,255 (80% power), 35,148 (90% power)
power.t.test: 6564.6 
Simulated power at n = 6,564 per arm: 0.799 (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. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome and four secondary outcomes. It does not report how the investigators planned to control the chance of false-positive findings across multiple outcomes or comparisons. No multiplicity adjustment, hierarchy of hypotheses, or designation of confirmatory and exploratory secondary tests is reported in the registry record. This matters because evaluating several outcomes can increase the chance that at least one result appears notable by chance. The unadjusted secondary p-values should therefore be interpreted cautiously and not as a set of independent confirmations.

Missing-data handling is not reported in the registry record. The record does not explain whether participants with unavailable follow-up measurements were excluded, whether any values were imputed, or whether the analysis used all randomized participants. The posted summaries list 29 participants in each arm, but that alone does not establish the analysis population or show whether all randomized participants contributed outcome data.

The analysis population is also not described. The registry record does not state whether results were analyzed according to randomized assignment, according to intervention received, or under another rule. It does not report exclusions, protocol deviations or adherence. Thus, the results cannot be classified as intention-to-treat or per-protocol on the basis of the record.

The record lists zero reported analyses and does not describe a statistical analysis plan. Details such as covariate adjustment, baseline handling, model choice, sensitivity analyses and interim analyses are not reported in the registry record. No claim about those procedures should be inferred from the posted summary statistics. These reporting gaps do not change the arithmetic of the unadjusted recalculations, but they limit how completely the study's intended analysis and the robustness of its findings can be assessed.

15. 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 lists 0 serious adverse events among 29 participants at risk in the 30-minute walking group and 0 among 29 at risk in the TV commercial stepping group. It also lists 0 other adverse events among 29 at risk in each group. These entries mean that no events in those categories are recorded in the posted safety summaries for the listed groups.

A zero count does not establish that an intervention is free of risk. Safety reporting depends on how events were defined, collected and recorded, and the registry record does not describe those procedures. The absence of a reported event in this record should not be interpreted as proof that no events occurred outside the recorded categories or observation period.

Deaths are listed as null for both groups, so death counts are not reported in the registry record. The record also lists no serious adverse event terms. These are descriptions of what is recorded, not broader conclusions about safety.

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

The primary posted comparison is an unadjusted estimated difference of 38 steps/day in mean change between the TV commercial stepping and 30-minute walking groups. Its 95% confidence interval, -361.9 to 437.9 steps/day, includes zero and spans differences in either direction. The data therefore leave considerable uncertainty about the size and direction of the average between-group contrast.

This result does not show that the two approaches are equivalent. Equivalence requires a prespecified margin and an analysis designed to evaluate whether the plausible difference is small enough to fall within that margin. Such a margin or analysis is not reported in the registry record. A non-significant p-value likewise does not prove there is no difference; it means the unadjusted result does not provide strong evidence against a zero-difference model under the calculation used.

The secondary results describe other measurements, but they do not establish a consistent overall effect across all outcomes. Because the registry record does not report the analysis plan or multiplicity handling, the secondary calculations are best treated as exploratory. A numerical result for TV viewing time is not reported in the registry record.

The randomized design is relevant to comparing assigned groups, but the record does not provide enough detail to evaluate implementation, adherence, masking procedures, missing data or the analysis population. It also does not report enough information to determine how representative the participants were. The findings therefore cannot be extended automatically to other populations or settings.

In short, the posted summaries provide an estimate of the difference in mean step-count change and an indication of its uncertainty. They do not establish an individual-level response, explain why any differences occurred, demonstrate equivalence, or support medical advice. The result should be understood as a limited statistical description of this completed trial's registry record.

17. Why This Trial Matters Statistically

This trial illustrates why an effect estimate and its uncertainty should be read together. The primary point estimate is close to zero in comparison with the range of values in its confidence interval, and the interval crosses zero. Reporting only the estimate or only the p-value would obscure how little precision the posted primary comparison provides.

It also illustrates the distinction between a randomized trial and a fully documented analysis. Randomization describes the assignment design, but the registry record does not report important analysis details such as missing-data handling, analysis population or covariate adjustment. These omissions limit the ability to assess how the posted summaries relate to the trial's original statistical plan.

The range of secondary outcomes is another statistical lesson. Measures of energy intake, weight and TV viewing time address related but distinct questions. When multiple outcomes are available and no multiplicity strategy is reported, a striking result among them should not be treated as definitive solely because its unadjusted p-value is small. Prespecification and transparent reporting help readers distinguish confirmatory questions from exploratory patterns.

Finally, planning calculations based on observed effects are not a description of the trial's design rationale. The planning illustrations show how sample-size requirements depend on the effect size chosen and desired power, under stated assumptions. They do not reconstruct what the investigators expected before the study began. Keeping those concepts separate helps prevent retrospective calculations from being mistaken for original design evidence.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record leaves important aspects of the trial and its analysis unspecified. It does not report eligibility criteria, participant characteristics, randomization methods, allocation concealment or which parties were masked. These omissions restrict assessment of who the findings apply to and how assignment and measurement were implemented.

The intervention description for TV commercial stepping is incomplete in the registry record. The record also does not report adherence, actual activity exposure, contamination between groups or other details needed to determine how closely participants followed their assigned instructions. No conclusions about compliance should be inferred from the outcome summaries.

For the primary outcome, the record does not describe the pedometer protocol, the timing or duration of measurement, or how the change score was calculated beyond the stated interval from 0 to 6 months. It does not report missing-data procedures, the analysis population, adjustments, sensitivity analyses or a statistical analysis plan. The posted comparisons are unadjusted recalculations from group summaries, rather than reported investigator analyses.

The record lists four secondary outcomes but provides numerical results for only three. It does not report a multiplicity strategy or clarify which secondary tests were prespecified. This makes the secondary pattern harder to interpret as confirmatory evidence. Safety entries are also limited to the recorded event counts; event definitions and collection procedures are not described, and death counts are not reported.

Finally, the primary confidence interval is broad and includes differences favoring either arm. The posted primary result is therefore imprecise. These limitations do not invalidate the recorded summaries, but they constrain the strength and scope of conclusions that can be drawn from them.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Physical Activity and Leisure-time Study (PALS) — NCT01342471.
• Registry record last updated 2012-11-09; status last verified 2012-10.
• Results first posted 2012-11-09.
• 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.

22. Record Summary

NCT01342471, the Physical Activity and Leisure-time Study (PALS), is listed as a completed, randomized, single-masked, parallel-group trial with phase PHASE1. The University of Tennessee is identified as sponsor. The registry record gives enrollment as 58, a start date of 2010-09 and primary completion in 2011-06.

The trial compared TV commercial stepping with a 30-minute walking program. Its primary outcome was change in pedometer-measured steps per day from 0 to 6 months. The posted unadjusted mean difference was 38 steps/day, with a 95% confidence interval from -361.9 to 437.9 steps/day and an unadjusted p-value of 0.852.

Secondary outcomes listed in the record were total energy intake, TV-related energy intake, weight and TV viewing time. Numerical results are posted for the first three; a numerical result for TV viewing time is not reported in the registry record. No investigator-reported analyses are listed, and several design and analysis details are not reported in the registry record.