Comparison of Bacteriostatic Saline to Buffered Lidocaine for Ultrasound Guided Hip Joint Injection Local Anesthesia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Bacteriostatic Saline to Buffered Lidocaine for Ultrasound Guided Hip Joint Injection Local Anesthesia (NCT02209272), a randomized phase 4 study. The primary outcome is VAS for Pain Score During Local Anesthesia Infiltration.

2. Clinical Question

3. Trial Design

The registry describes a completed Phase 4, randomized, parallel-group trial with quadruple masking. The interventions were bacteriostatic saline and buffered lidocaine, each used for local anesthesia during ultrasound-guided hip joint injection. Enrollment was 68. The registry does not report how the randomization sequence was generated, how allocation was concealed, or which specific groups of people were masked; those details are not reported in the registry record.

The primary outcome was a continuous pain score during local anesthetic infiltration. The registry lists the assessment timeframe as baseline to 5-10 minutes later, immediately after administration of the local anesthetic. The reported group summaries include 32 participants in the bacteriostatic saline group and 36 in the buffered lidocaine group. The registry also reports pain during the subsequent hip joint injection and anesthetic infiltration duration as secondary outcomes.

The posted analysis compares the two groups using a two-sided t-test for each reported outcome. It gives p-values for the primary and secondary comparisons but does not report the test statistic, degrees of freedom, or analysis population definition. The registry record does not describe the planned sample-size justification, original design assumptions, any interim analyses, the handling of missing outcome data, or whether the analysis followed an intention-to-treat or per-protocol approach. These cannot be inferred from the enrollment or the posted group summaries.

The registry reports completion and gives primary completion as 2018-02. It does not provide further detail in the trial design information about recruitment procedures, the clinical setting, or participant follow-up beyond the outcome timeframes. These omissions limit assessment of how the planned methods were implemented, even though the record provides the main design classification and outcome summaries.

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 VAS for Pain Score During Local Anesthesia Infiltration, measured over baseline to 5-10 minutes later -- immediately after local anesthetic injection administration.

The primary endpoint is the Visual Analog Scale pain score during local anesthetic infiltration. The registry describes the measure as a validated tool using a 100mm horizontal line anchored at 0 for no pain and 100 for pain as bad as it could be. The assessment was recorded immediately after local anesthetic administration, with the timeframe described as baseline to 5-10 minutes later. The outcome is reported as a group mean with a standard deviation.

This endpoint captures pain associated with infiltration itself, rather than pain during the later hip joint injection. That distinction matters because the trial asks about local anesthesia for the injection procedure: the discomfort of administering the anesthetic is a different stage from the pain experienced during the subsequent procedure. The registry separately lists pain during the subsequent injection as a secondary measure of anesthetic efficacy.

As a continuous score, the endpoint can be summarized by a mean and standard deviation, and the groups can be compared by a difference in means. A mean describes the group’s average score; a standard deviation describes variation among individual scores around that average. Those summaries do not show the full distribution of scores or how many participants experienced particular levels of pain. The registry does not report a threshold for a clinically important difference, so statistical comparisons alone do not establish whether a difference would be meaningful to patients.

7. Results Posted in the Registry

• Buffered Lidocaine: mean 14.00 versus 13.20 on control; difference 0.80 (95% CI -6.02 to 7.62), standardized effect d = 0.06; z-test p = 0.818.

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.

VAS for Pain Score During Subsequent Hip Joint Injection (Local Anesthetic Efficacy)

• 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:
  • Buffered Lidocaine: mean 15.60 versus 20.70 on control; difference -5.10 (95% CI -12.93 to 2.73), standardized effect d = -0.32; z-test p = 0.202.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Buffered Lidocaine and the control. The interval gives the range of effects that remain compatible with the data.

Anesthetic Infiltration Duration

• 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:
  • Buffered Lidocaine: mean 32.70 versus 33.30 on control; difference -0.60 (95% CI -2.86 to 1.66), standardized effect d = -0.13; z-test p = 0.603.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Buffered Lidocaine and the control. The interval gives the range of effects that remain compatible with the data.

Across the two secondary outcomes, the mean differences lean in different directions: the pain-score comparison during the subsequent injection is lower in the buffered lidocaine group, while the duration comparison is slightly lower in that group as well. The reported and recalculated tests do not indicate statistically clear differences for either outcome, and both recalculated intervals include zero. Read together with the primary outcome, the secondary results do not produce a consistent pattern of clear separation between groups across the measured outcomes.

The secondary outcomes address related but distinct aspects of the procedure. Pain during the subsequent hip joint injection concerns the anesthetic efficacy outcome, whereas infiltration duration measures the time taken for anesthetic infiltration. Neither is interchangeable with the primary assessment of pain during infiltration. Taken as a group, they add context to the primary question but do not resolve its uncertainty.

The registry reports two-sided t-tests for the secondary comparisons but does not report an adjustment for testing multiple outcomes, a hierarchy for interpreting them, or a multiplicity plan. General explanation: when several hypotheses are tested, the chance of at least one apparently unusual result can increase if each is interpreted without accounting for the set of tests. Unadjusted secondary results therefore carry less weight as confirmatory evidence, especially when the analysis plan is not described. The record does not report whether the secondary outcomes were prespecified in a detailed protocol or how they were intended to affect interpretation.

The values should be considered as estimates with uncertainty, rather than isolated pass-or-fail tests. The registry does not provide clinically important thresholds for these measures, nor does it report a model that combines outcomes. The secondary results can suggest questions for further investigation, but the posted information alone does not justify treating them as proof of a difference or of equivalence.

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

• VAS for Pain Score During Subsequent Hip Joint Injection (Local Anesthetic Efficacy)
• Anesthetic Infiltration Duration

9. Statistical Interpretation

10. Statistical Methods Explained

The registry reports continuous outcomes as means and standard deviations, and reports two-sided t-tests for comparisons between the two groups. The recalculated contrasts and confidence intervals are simple unadjusted calculations from the posted summary statistics. General explanation follows: these methods provide a comparison of group averages and an estimate of uncertainty, but they do not replace information about the trial’s original protocol or analysis plan.

What does a mean difference describe?

A mean difference subtracts one group’s average from the other group’s average. The comparison in these results is expressed as buffered lidocaine minus bacteriostatic saline. A positive value therefore indicates a higher average score in the buffered lidocaine group; a negative value indicates a lower average score in that group. For pain scores, the direction describes the group averages and does not, on its own, establish clinical importance. The registry does not report a threshold that would define an important difference.

Why are standard deviations reported?

General explanation: a standard deviation describes how dispersed individual observations are around their group mean. A small standard deviation indicates that observations are more tightly clustered around the mean, while a larger one indicates greater spread. It is not the same as the standard error, which describes the estimated uncertainty of a group mean. Individual outcomes can vary considerably even when group means are similar. The summaries do not reveal the shape of each outcome distribution, possible outliers, or participant-level patterns.

What does the t-test assess?

General explanation: a two-sided t-test evaluates whether the observed difference between group means is sufficiently inconsistent with a null hypothesis of no mean difference, under the test’s assumptions. “Two-sided” means that differences in either direction count as evidence against that null hypothesis. A p-value is not the probability that the null hypothesis is true, nor does it measure the size or clinical importance of a difference. Its interpretation depends on the analysis and assumptions; the registry does not report diagnostic checks or the test statistic.

The posted record lists a t-test, 2 sided, for each outcome. It does not say whether a particular pooled-variance or unequal-variance version was used, or provide additional modeling details. The recalculated results are explicitly unadjusted comparisons of the posted summaries; they do not account for covariates, clustering, or other factors. No such adjustments are described in the registry record.

How should a confidence interval be read?

General explanation: a confidence interval gives a range of values that are compatible with the observed data under the method used. Its width conveys precision: a wider interval represents less precise estimation than a narrower one. An interval spanning zero indicates that the data are compatible with no mean difference as well as with differences in either direction, at the confidence level used. The registry does not report the confidence level for the recalculated intervals, so it should not be assigned a percentage based on assumption.

A confidence interval is not a guarantee that the true value lies within its particular limits, and it does not indicate which values are clinically important. It should be read alongside the point estimate, the scale, the variability, and any relevant clinical threshold. No such threshold is reported.

Why does over-dispersion matter in general?

General explanation: when observed outcomes vary more than a statistical model assumes, standard errors can be too small and uncertainty can be understated. For continuous outcomes, the reported standard deviations give a direct summary of observed spread, but they do not establish that every assumption of a t-test is satisfied. The registry does not report a formal assessment of distributional assumptions, and the available group summaries are not enough to reconstruct one.

For the primary comparison, the recalculated estimate is 0.8 and its interval runs from -6.016 to 7.616. Its unadjusted recalculated p-value is 0.818, while the registry reports 0.82. The analysis is consistent in direction and broad interpretation across these reported forms, but the interval is the more informative description of the range of mean differences compatible with the calculation. Neither the p-value nor interval resolves whether any difference would matter clinically.

11. Confidence Intervals and Precision

The primary mean difference is 0.8 points, with the comparison defined as buffered lidocaine minus bacteriostatic saline. Its recalculated confidence interval extends from -6.016 to 7.616. Because the interval spans zero, the data are compatible with a small difference in either direction as well as no mean difference. The estimate is not precise enough to narrow the plausible contrast to one side of zero. The registry does not report the confidence level used for the recalculated interval, so no confidence percentage is stated.

General explanation: an interval’s width reflects the uncertainty in an estimate, given the data and method. A narrow interval can exclude a broader range of possible effects; a wide interval leaves more values compatible with the observations. Precision is distinct from clinical importance: even a precise estimate may not answer whether an effect matters, and an imprecise estimate may include both small and larger effects. The registry does not report a clinical importance threshold for this score.

The primary group summaries include 32 participants with a standard deviation of 15.0 in the bacteriostatic saline group and 36 participants with a standard deviation of 13.5 in the buffered lidocaine group. These summaries indicate variation among participants, while the interval reflects uncertainty about the contrast between group means. The trial’s enrollment and the variability in the scores are relevant context for interpreting the width of that interval, but they do not justify treating a non-significant test as proof of no difference.

The intervals for the secondary outcomes also include zero: -12.93 to 2.727 for pain during the subsequent injection and -2.858 to 1.658 for infiltration duration. The registry does not report confidence levels for these recalculated intervals either. These estimates should be understood as uncertain group contrasts, not as definitive evidence of identical outcomes.

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. The posted illustration uses a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It considers effects equal to 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. For each assumed effect, the 80% power column describes the participants per arm indicated by the calculation to provide an 80% probability of detecting that effect under the stated assumptions; the 90% power column gives the corresponding planning figure for a 90% probability. These are design probabilities under assumed conditions, not guarantees about a future study.

For the primary outcome, the illustration lists 4,963 participants per arm for 80% power and 6,644 participants per arm for 90% power when planning for 100% of the observed effect. Planning for 75% of the observed effect gives 8,823 participants per arm for 80% power and 11,811 participants per arm for 90% power. Planning for 50% of the observed effect gives 19,851 participants per arm for 80% power and 26,575 participants per arm for 90% power. The pattern reflects a general principle: smaller assumed effects require more participants to detect under otherwise fixed assumptions.

These figures are planning illustrations computed from the observed effect, not the trial’s original design justification. The trial’s own sample-size assumptions are not reported in the registry record. 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 = 0.800; pooled standard deviation σ = 14.224.
2. n = 2 × (1.96 + 0.842)² × 14.224² / 0.800² = 4,962.7, rounded up to 4,963 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 <- 0.800000000000001                      # observed difference in means
sigma <- 14.2242590476462                     # 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(2209272)
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 = 4,963 (80% power), 6,644 (90% power)
 75% of observed effect: n per arm = 8,823 (80% power), 11,811 (90% power)
 50% of observed effect: n per arm = 19,851 (80% power), 26,575 (90% power)
power.t.test: 4963.6 
Simulated power at n = 4,963 per arm: 0.794 (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 registry-reported primary analysis is a two-sided t-test with p = 0.82. The simple unadjusted recalculation from the posted group summaries gives p = 0.818 and a mean difference of 0.8, with a confidence interval from -6.016 to 7.616. The recalculated comparison is close to the reported p-value and leads to the same broad reading: the posted analysis does not show a statistically clear difference in the primary group means.

The registry does not report the sponsor’s estimated mean difference or confidence interval for this primary comparison; those values are absent from the posted analysis result. The recalculated estimate and interval should therefore be understood as additional unadjusted calculations from the group means, standard deviations, and sample sizes, not as a replacement for a full analysis report.

The record does not flag a discrepancy between the reported analysis and the recalculation. Where the two are consistent, the reported analysis remains the trial’s stated analysis and the recalculation is a transparent supplement based on summary data. It does not reveal whether the sponsor used additional protocol-specified procedures that are not described in the record.

15. Multiplicity, Missing Data and Analysis Populations

The registry reports one primary outcome and two secondary outcomes, each with a two-sided t-test. It does not report a multiplicity adjustment, a testing hierarchy, or a prespecified strategy for controlling the interpretation of several comparisons. That absence matters because interpreting multiple p-values independently can overstate the strength of evidence from any single secondary finding. The primary outcome is the stated main endpoint; the secondary outcomes should be read as supportive or exploratory unless a fuller analysis plan indicates otherwise.

The record does not report whether outcomes were analyzed according to intention to treat, per protocol, or another analysis population. It also does not provide a participant flow by analysis, describe exclusions, or state how missing outcome measurements were handled. The group summaries report 32 participants for bacteriostatic saline and 36 for buffered lidocaine, but those figures alone do not establish that every randomized participant contributed to every outcome or explain any missingness.

The registry does not report imputation procedures, sensitivity analyses for missing data, or comparisons between participants with and without measured outcomes. Missingness can affect estimates if the availability of an outcome is related to the outcome itself or to group assignment. Without details, the direction or size of any such effect cannot be assessed.

The posted record also does not describe interim analyses, stopping rules, protocol deviations, or the original statistical analysis plan. It would be inappropriate to infer that these procedures were absent; they are simply not reported in the registry record. These gaps constrain assessment of whether the posted results follow prespecified methods and how robust the findings are to alternative analytic choices.

These reporting limitations do not invalidate the numerical summaries, but they narrow what can be concluded from them. The stated group comparisons can be described as posted, while claims about multiplicity control, missing-data methods, analysis populations, and protocol adherence cannot be verified from 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.

The registry reports zero serious adverse events among 32 participants at risk in the bacteriostatic saline group and zero among 36 participants at risk in the buffered lidocaine group. It also reports zero other adverse events among 32 and 36 participants at risk, respectively, and zero deaths in either group. No serious adverse event terms are listed.

These figures describe the events recorded in the registry for the reported groups. They do not demonstrate that the risk of an adverse event is zero, and they do not establish that the two approaches have identical safety profiles. When no events are recorded, the data still leave uncertainty about events that might occur in a larger population or with different observation and reporting conditions.

The registry does not provide further detail about the duration or method of adverse-event monitoring, event definitions, severity grading, or relatedness to the intervention. It also does not report individual event narratives. The counts should therefore be interpreted as the posted safety summary, not as a complete characterization of all possible harms.

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

The trial provides a randomized comparison of bacteriostatic saline and buffered lidocaine for local anesthesia during ultrasound-guided hip joint injection. For its primary measure, average pain during local anesthetic infiltration was similar in the two groups in the sense that the reported test did not indicate a statistically clear difference. The estimate and interval remain uncertain and include differences in either direction. The record does not establish equivalence, because it reports no equivalence margin or non-inferiority framework.

The results concern the specific outcomes, procedure, and participants described in the registry. The primary score measures pain during anesthetic infiltration, not every aspect of the injection experience. The registry’s secondary measures address pain during the subsequent injection and infiltration duration, but the record does not supply a broader set of patient-centered outcomes or a clinically important threshold for interpreting score differences.

A p-value above a conventional significance threshold is not proof that two interventions have the same effect. Likewise, a numerical difference is not automatically clinically meaningful. The confidence interval provides a range of estimates compatible with the calculation, while the absence of a reported clinical threshold leaves the practical importance of those estimates unresolved.

The posted data do not establish what would happen in other clinical settings, with different procedures, or in populations not described in the record. Details about eligibility, missing data, analysis populations, and the original sample-size rationale are not reported. Those limitations make it important to keep interpretation tied to the available summaries rather than extend the results beyond their scope.

In short, the registry describes no statistically clear group difference in the primary mean score and reports no adverse events in either group. These observations are bounded by the trial’s enrollment, reported outcome summaries, and the information available in the registry; they should not be taken as proof of no difference or as a general treatment recommendation.

18. Why This Trial Matters Statistically

This trial illustrates why a non-significant test and a claim of equivalence are not interchangeable. The primary comparison has a mean difference close to zero, but the interval also includes nonzero values on both sides. Without a prespecified equivalence or non-inferiority margin, the result answers a conventional difference question rather than establishing that the approaches are sufficiently similar for a defined purpose.

It also shows the value of reporting estimates and uncertainty, rather than relying on p-values alone. The registry’s reported p-value indicates that the primary test did not find a statistically clear difference, while the recalculated interval communicates the range of plausible mean contrasts under the calculation. Neither statistic provides a clinical importance threshold, so statistical uncertainty and practical importance remain separate questions.

Another statistical lesson is that the primary endpoint and secondary outcomes measure distinct parts of the procedure. A single outcome cannot stand in for all aspects of pain or procedure experience. At the same time, multiple outcomes need a clear interpretation plan: without reported multiplicity handling, secondary p-values should not be treated as independent confirmatory evidence.

Finally, the sample-size illustration demonstrates how planning depends on the effect selected for detection. Smaller assumed effects require larger planned groups under the stated assumptions. These are planning calculations based on the observed effect, not a retrospective measure of the trial’s success or failure. The original sample-size assumptions are not reported, underscoring the importance of a transparent design rationale and analysis plan.

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 are specific to the information reported for this trial. Enrollment was 68, with group summaries based on 32 participants in the bacteriostatic saline group and 36 in the buffered lidocaine group. The primary interval spans zero and includes differences in either direction, so the estimate does not precisely isolate a single direction of effect. No clinically important threshold for the pain score is reported.

The registry provides only a brief description of the population and procedure. Hip pain is listed as the condition, and the interventions are described for ultrasound-guided hip joint injection, but detailed eligibility criteria, recruitment setting, and participant characteristics are not reported. The extent to which results apply beyond the enrolled participants and described procedure cannot be assessed from these details.

Although the design is described as randomized and quadruple-masked, the record does not describe sequence generation, allocation concealment, or which parties were masked. It also does not report the original sample-size justification, the statistical analysis plan, interim analyses, missing-data handling, or analysis population. These omissions prevent a full assessment of design implementation and analytic robustness.

The reported tests do not include a stated adjustment for multiple comparisons. The registry also provides limited safety detail beyond event counts, with no serious adverse events, other adverse events, or deaths reported in the group summaries. Monitoring duration and adverse-event ascertainment procedures are not reported. These limits restrict interpretation of both efficacy-related outcomes and safety reporting; they do not, on their own, establish that unreported procedures were not used.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: Comparison of Bacteriostatic Saline to Buffered Lidocaine for Ultrasound Guided Hip Joint Injection Local Anesthesia — NCT02209272.
• Registry record last updated 2019-04-11; status last verified 2019-04.
• Results first posted 2019-04-02.
• 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 describes a completed Phase 4, randomized, parallel-group trial with quadruple masking and enrollment of 68. It compared bacteriostatic saline with buffered lidocaine for local anesthesia during ultrasound-guided hip joint injection.

The primary outcome was pain during local anesthetic infiltration, measured with a Visual Analog Scale. Group means were 13.2 and 14.0, and the recalculated unadjusted mean difference was 0.8, with a confidence interval from -6.016 to 7.616. The registry-reported two-sided test gave p = 0.82.

The record also reports two secondary outcomes and zero serious adverse events, other adverse events, and deaths in both groups. It does not report the original sample-size rationale, detailed analysis plan, multiplicity handling, or missing-data methods. The posted results do not establish equivalence or determine the clinical importance of any possible difference.