Two-way Intraclass Correlation Coefficients Research Articles

Validating rasterstereography to evaluate thoracic kyphosis in patients with Scheuermann's disease.

Evaluate the validity of rasterstereography compared to low-dose, biplanar spine radiography for assessing thoracic kyphosis (TK) angles in Scheuermann's disease patients. This prospective study included all the Scheuermann's disease patients consulting our clinic from 2016 to 2018. Recruited patients underwent two-dimensional low-dose biplanar anteroposterior full-length spine radiography and rasterstereography on the same day. Relationships between the TK angles measured were evaluated using Pearson correlation coefficients. Agreement between radiographic and rasterstereographic TK angles was evaluated using two-way intraclass correlation coefficients (ICCs) and Bland-Altman plots. Proportional biases were assessed using the slope regression lines fitted to Bland-Altman plots. The mean demographic and radiological characteristics of the 52 patients (20 girls; 39%) included were: age 13.1 ± 2years; BMI 17.3 ± 2.8; and TK max. 50.4° ± 10°. Rasterstereographic TK angles were strongly correlated with radiographic TK angles evaluated from T2-T12 (r = 0.677) and from C7-Max (r = 0.704), with 'good' agreement (ICC > 0.75). A proportional bias was revealed in the slope regression line fitted to the Bland-Altman plot from the C7-Max radiography and the rasterstereography measurements (p = 0.034) but not from the T2-T12 and rasterstereographic TK angles (p = 0.997). Rasterstereography is a reliable means of quantifying TK angles in Scheuermann's disease patients. It could directly reduce the number of radiographic scans patients need over time, minimising their radiation exposure.

Improving alcohol health literacy and reducing alcohol consumption: recommendations for Germany

BackgroundAlthough the detrimental health effects of alcohol are well established, consumption levels are high in many high-income countries such as Germany. Improving alcohol health literacy presents an integrated approach to alcohol prevention and an important complement to alcohol policy. Our aim was to identify and prioritize measures to enhance alcohol health literacy and hence to reduce alcohol consumption, using Germany as an example.MethodsA series of recommendations for improving alcohol health literacy were derived from a review of the literature and subsequently rated by five experts. Recommendations were rated according to their likely impact on enhancing (a) alcohol health literacy and (b) reducing alcohol consumption. Inter-rater agreement was assessed using a two-way intra-class correlation coefficient (ICC).ResultsEleven recommendations were established for three areas of action: (1) education and information, (2) health care system, and (3) alcohol control policy. Education and information measures were rated high to increase alcohol health literacy but low to their impact on alcohol consumption, while this pattern was reversed for alcohol control policies. The ratings showed good agreement (ICC: 0.85–0.88).ConclusionsImproving alcohol health literacy and reducing alcohol consumption should be considered complementary and become part of a comprehensive alcohol strategy to curb the health, social, and economic burden of alcohol.

Inter- and Intra-observer Agreement of Visual Estimation, Goniometric and Radiographic Measurement of Passive Thumb Metacarpophalangeal Joint Hyperextension.

Background: Reliable methods for measuring range of motion is important for hand therapists. Currently, there is no gold standard for the measurement of thumb metacarpophalangeal joint (MCPJ) hyperextension. We hypothesised that visual and goniometric measurements of thumb MCPJ hyperextension vary greater than 10° from radiographic measurements, and between observers. Methods: Twenty-six fresh-frozen hands were measured by a senior orthopaedic resident and fellowship trained hand surgeon. Passive thumb MCPJ hyperextension was measured by visual estimation, goniometry and axis measurement on a lateral thumb radiograph. Raters were blinded to each other's and their own prior measurements. Descriptive statistics were recorded for measurement type and inter-observer agreement using a two-way intra-class correlation coefficient (ICC). Intra-observer agreement was calculated using concordance correlation coefficient (CCC). Bland-Altman plots identified trends, systemic differences or potential outliers. Results: Mean measurements for both raters were similar for visual estimation and radiographic measurements. Mean goniometric measurements were twice as high for Rater B, and closer to radiographic measurements. For both raters, mean radiographic measurements were 10° greater than the other two methods. For inter-rater agreement, measurements were within 10° most frequently with radiographic measurement, then visual estimates, and least by goniometer measurements. Rater B had better agreement comparing visual and goniometric to radiographic measurements. Conclusions: Radiographic measurement has the best inter-observer agreement and precision for evaluating passive thumb MCPJ hyperextension, especially considering adjunct corrective procedures when performing a soft-tissue basal joint arthroplasty. Rater experience improves precision, but there is still poor agreement between visual estimates and goniometer measurements compared to radiographic measurements, as the former two underestimate hyperextension by 10°. Development of a standard method of clinical measurement is needed to improve reliability.

How Many Days Of Monitoring are Necessary to Accurately Characterize Activity of Parkinson's Disease Patients?

<h3>Research Objectives</h3> To determine a reliable sampling strategy to accurately characterize physical activity in individuals with Parkinson's disease (PD). <h3>Design</h3> Observational study with individuals with PD wearing a wrist worn activity monitor for 30 days. <h3>Setting</h3> General community. <h3>Participants</h3> Individuals with mild-Moderate Parkinson's disease (N=31). <h3>Interventions</h3> Not applicable. <h3>Main Outcome Measures</h3> A step/day measurement period of various lengths (2, 3, 4, 5, 6, 7, and 14 days) were selected for consecutive and random days. Two-way intraclass correlation coefficients (ICC) were calculated for ten samples of both consecutive and random days for each participant. The ten samples were averaged for ICC for each measurement period. <h3>Results</h3> The ICC averages for consecutive days ranged from 0.59-0.75, with stability of ICC starting at a 7-day measurement period (95% CI, 0.55- 0.80). The ICC averages for random days ranged from 0.59-0.71, with stability of ICC maintained starting with a random 7-day measurement period (95% CI, 0.51- 0.77). <h3>Conclusions</h3> PD-related variability in motor behavior, and conventional methods of a four day measurement period may not accurately reflect physical activity behavior. Identifying a method to accurately characterize level of physical activity in individuals with PD over time provides those conducting short- and long-term intervention studies and trials with a robust physical activity outcome. The results of this study indicate that seven consecutive days of physical activity monitoring was the most stable measure of physical activity. For random sampling days, seven days also resulted in the greatest and most stable ICC of that sampling method. Therefore, in PD a seven-day consecutive measurement period may be the most representative of physical activity behavior in individuals with PD. <h3>Author(s) Disclosures</h3> No authors have disclosures or conflicts.

Monitoring of Palliative Care Symptoms and Concerns in Specialized Palliative Home Care Using an Electronic Version of the Integrated Palliative care Outcome Scale (Palli-MONITOR): protocol for a mixed-methods study

IntroductionOver the last decades, patient-reported outcome (PRO) measures have been developed to better understand the patient’s perspective and enable patient-centred care. In palliative care, the Integrated Palliative care Outcome Scale...

Abstract No. 454 Crowd-sourced assessment of interventional radiology technical skill: a method to guide future training of interventional radiologists

Crowd sourced assessment of surgical skill using standardized evaluation has been demonstrated in the literature to be as accurate as expert opinion. A small pilot study demonstrated translation of this task to interventional radiology (IR). Here, next steps in the development of a grading scale for IR technical skill is pursued with further evaluation of the accuracy of a crowd-sourced assessment. Three simulator performances of prostate artery catheterization and embolization performed by IR trainees were recorded. A survey was created consisting of a 13-question grading scale specific to prostate artery embolization (PAE) and a 10-question grading scale on general IR technical skills. 50 Amazon Mechanical Turk (MTurk) workers and 5 IR faculty viewed the three videos and completed the entire assessment. The MTurk grading was compared with that of the experienced IR faculty. Means and standard deviations were calculated for individual items and in aggregate across videos. To determine interrater reliability among faculty, a two-way intraclass correlation coefficient was calculated per each item. Dissimilar from multiple prior studies, the MTurk workers did not replicate expert scoring. In contradistinction, when questions were considered in aggregate, the MTurk workers rated lowest (mean, 2.71; standard deviation [SD], 1.06) the video rated highest (mean, 2.83; SD, 0.88) by the faculty, and rated highest (mean, 2.83; SD, 0.99) the video rated lowest (mean, 1.61; SD, 0.83) by the faculty. However, IR faculty were noted to demonstrate decent inter-rater reliability with interreader agreement for 15 of 23 items (65%) at a threshold of P = 0.05. Although initial data has suggested that IR technique may be successfully graded by standardized evaluation, this data suggests that the complexity and intricacy of more advanced technical evaluation may not be as well suited to crowd sourced assessment. However, the good level of inter rater reliability among faculty, most notably of the poorly skilled video, suggest standardized evaluation by experienced faculty may have merit. Further study is needed to refine and validate the evaluation form.

Comparison of automated and manual protocols for magnetic resonance imaging assessment of liver iron concentration.

ObjectiveTo compare automated and manual magnetic resonance imaging protocols for estimating liver iron concentrations at 1.5 T.Materials and MethodsMagnetic resonance imaging examination of the liver was performed in 53 patients with clinically suspected hepatic iron overload and in 21 control subjects. Liver iron concentrations were then estimated by two examiners who were blinded to the groups. The examiners employed automated T2* and T1 mapping, as well as manual T2* and signal-intensity-ratio method. We analyzed accuracy by using ROC curves. Interobserver and intraobserver agreement were analyzed by calculating two-way intraclass correlation coefficients.ResultsThe area under the ROC curve (to discriminate between patients and controls) was 0.912 for automated T2* mapping, 0.934 for the signal-intensity-ratio method, 0.908 for manual T2*, and 0.80 for T1 mapping, the last method differing significantly from the other three. The level of interobserver and intraobserver agreement was good (intraclass correlation coefficient, 0.938-0.998; p < 0.05). Correlations involving T1 mapping, although still significant, were lower.ConclusionAt 1.5 T, T2* mapping is a rapid tool that shows promise for the diagnosis of liver iron overload, whereas T1 mapping shows less accuracy. The performance of T1 mapping is poorer than is that of T2* methods.

Abstract 5684: A methodology for designing and validating computational pathology scores for immune cell clustering in tumor biopsies

Abstract Abstract: Introduction: Immune cell clustering is commonly observed in histopathology images. As the frequency and nature of immune cell clustering may represent biological phenomenon critical to response to immunotherapy, it is an import feature to measure for differentiating immune phenotypes which may predict patient response to immune modulating therapy. Computational pathology data sets and unsupervised machine learning approaches are capable of describing immune cell clustering using a variety of methods. However, it has not been clear how such measurements might be applied to generate a validated computational pathology score that truly captures the immune phenotype sought to score. This work explores a methodology for the development and analytical validation of digital pathology scores for immune cell clustering derived from the application of unsupervised learning to digital pathology data sets. Methods and Experimental Design: Computational pathology data derived with Flagship's cTA™ (Computational Tissue Analysis) platform from 12 NSCLC biopsy samples stained with a validated CD8 -Ki67 duplex IHC assay was used to create a virtual library of scores that described the clustering of CD8+ staining cells. The library was created by using different combinations of clustering methods, parameters, and scoring schemes. Scores with high distinguishability measured through a two-way intraclass correlation coefficient, inter-run precision measured through the coefficient of variation, and dynamic range were considered analytically validated. Principal component analysis and hierarchical clustering of the analytically validated scores were used to further optimize selection of the most informative subset of clustering scores from the library. Results and Conclusions: 17 clustering scores passed the validation criteria. 4 of these 17 scores appear to be relatively uncorrelated with each other and capture unique information about the spatial relationships of CD8 positive cells. A further analysis of these scores demonstrates the ability to distinguish different immune cell clustering profiles in samples that contain similar biomarker expression levels using the common scoring methods of both overall percentage of positive cells and percentage of positive cells per tissue area. This process for screening and analytically validating a virtual library of computational biomarker scores appears to hold much promise for bringing cluster-derived computational pathology scores into future clinical applications in a way that is analogous to analytical validation of traditional IHC assays in support of oncology drug development. Citation Format: Logan Cerkovnik, Karen Ryall, G David Young, Kristen Wilson, Joseph Krueger. A methodology for designing and validating computational pathology scores for immune cell clustering in tumor biopsies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5684.

Reproducibility of ultrasound-derived muscle thickness and echo-intensity for the entire quadriceps femoris muscle

IntroductionMuscle thickness (MT) and muscle echo-intensity (EI) allow the study of skeletal muscle adaptive changes with ultrasound. This study investigates the intra- and inter-session reliability and agreement of MT and EI measurements for each of the four heads of the quadriceps femoris in transverse and longitudinal scans, using two sizes for the region of interest (ROI); EI measurements only. MethodsThree B-mode images from two views were acquired from each head of quadriceps femoris from twenty participants (10 females) in two sessions, 7 days apart. EI was measured using a large and a small ROI. Reliability was examined with the mixed two-way intra-class correlation coefficient (ICC), the standard error of mean (SEM) and the smallest detectable change (SDC). Bland–Altman's plots were used to study agreement. ResultsHigh to very high inter-session ICC values were found for MT for all muscle heads, particularly for measurements from transverse scans. For EI measurement, ICC values ranged from low to high, with higher ICC values seen with the largest ROI. SDC values ranged between 0.19 and 0.53 cm for MT and between 3.73 and 18.56 arbitrary units (a.u.) for two ROIs. Good agreement existed between MT measurements made in both scans. A small bias and larger 95% limits of agreement were seen for EI measurements collected with the two ROI sizes. ConclusionUltrasound measures of MT and EI show moderate to very high reliability. The reliability and agreement of MT and EI measurements are improved in transverse scans and with larger ROIs.

An evaluation of the psychometric properties of the Indicator of Relative Need (IoRN) instrument.

BackgroundThe Indicator of Relative Need (IoRN) instrument is designed for both health and social care services to measure function and dependency in older people. To date, the tool has not undergone assessment of validity. We report two studies aimed to evaluate psychometric properties of the IoRN.MethodsThe first study recruited patients receiving social care at discharge from hospital, those rehabilitating in intermediate care, and those in a rehabilitation at home service. Participants were assessed using the IoRN by a single researcher and by the clinical team at baseline and 8 weeks. Comparator instruments (Barthel ADL, Nottingham Extended ADL and Townsend Disability Scale) were also administered. Overall change in ability was assessed with a 7 point Likert scale at 8 weeks. The second study analysed linked routinely collected, health and social care data (including IoRN scores) to assess the relationship between IoRN category and death, hospitalisation and care home admission as a test of external validity.ResultsNinety participants were included in the first study, mean age 77.9 (SD 12.0). Cronbach’s alpha for IoRN subscales was high (0.87 to 0.93); subscales showed moderate correlation with comparator tools (r = 0.43 to 0.63). Cohen’s weighted kappa showed moderate agreement between researcher and clinician IoRN category (0.49 to 0.53). Two-way intraclass correlation coefficients for IoRN subscales in participants reporting no change in ability were high (0.88 to 0.98) suggesting good stability; responsiveness coefficients in participants reporting overall change were equal to or better than comparator tools. 1712 patients were included in the second study, mean age 81.0 years (SD 7.7). Adjusted hazard ratios for death, care home admission and hospitalisation in the most dependent category compared to the least dependent IoRN category were 5.9 (95 % CI 2.0–17.0); 7.2 (95 % CI 4.4–12.0); 1.1 (95 % CI 0.5–2.6) respectively. The mean number of allocated hours of care 6 months after assessment was higher in the most dependent group compared to the least dependent group (5.6 vs 1.4 h, p = 0.005).ConclusionsFindings from these analyses support the use of the IoRN across a range of clinical environments although some limitations are highlighted.

Prostate Imaging: Evaluation of a Reusable Two-Channel Endorectal Receiver Coil for MR Imaging at 1.5 T

To prospectively compare image quality with use of a two-channel solid reusable phased-array endorectal receiver coil (SPAC) with that of the single-channel inflatable endorectal balloon coil currently in widespread use for 1.5-T magnetic resonance (MR) imaging of the prostate. Institutional review board approval and informed consent were obtained. Multiparametric prostate MR imaging at 1.5 T was performed in patients who were suspected of having cancer. Thirty consecutive patients were included (mean age, 66.1 years; range, 49-76 years). The first 15 patients were imaged by using a balloon coil and an eight-channel external array, and the remaining 15 were imaged with a SPAC alone. One patient was imaged with both techniques. Axial T2-weighted images acquired at both standard and high spatial resolution were used to compare image quality between coils. Qualitative assessments of image quality were made separately by three radiologists. Signal-to-noise ratio (SNR) profiles were determined on a pixel-by-pixel basis in a 1-cm central band in the prostate by using T1-weighted axial images at the apex, midgland, and base. Interrater reliability was determined by using a two-way intraclass correlation coefficient, qualitative scores were compared by using the Student t test for independent samples, and SNR profiles were plotted by using a Biot-Savart curve approximation. SNR of the SPAC was significantly better compared with that of the balloon coil at distances up to 3.0 cm at the apex and 3.5 cm at the base and midgland (P < .001). There was a 7% improvement in SNR at the mean maximal anteroposterior prostate dimension in this cohort and a 96% improvement at half this distance. At both standard and high spatial resolution, significant improvements in overall image quality (P = .015 and P < .001, respectively), visibility of the anterior gland (P = .009 and P < .001, respectively), and noise (P < .001 and P < .001, respectively) were seen when the SPAC was used. Interrater reliability was 0.536 (95% confidence interval: 0.461, 0.603). Both SNR and image quality were significantly improved with use of the SPAC at 1.5 T compared with use of the single-channel inflatable endorectal balloon coil.

A CONSORT Clinical Trial Reporting Compliance Audit of the Oncology Randomized Controlled Trial Literature

Introduction: The Consolidated Standards for Reporting Trials (CONSORT) checklist has been formulated to improve the reporting of randomized controlled trials (RCTs). This investigation aims to determine predictors of CONSORT checklist compliance in the oncology literature. Methods: Eight-hundred and fifty articles assessing interventions in adult breast, prostate, colorectal, and lung cancer between 1992-2010 were identified by a systematic search. Exclusion criteria included investigations reporting interim/secondary/long-term update analyses, pilot/phase 2/non-parallel design studies. After full article review, 408 RCTs were eligible for inclusion. RCT descriptive variables including number of authors/study patients, 2009 journal impact factor/journal classification, type of cancer and therapeutic intervention, publication year, primary study country, and cooperative group involvement were captured for all trials. Two qualified auditors assessed all manuscripts in order to generate average and difference CONSORT checklist scores related to the observers. Results: Mean average CONSORT score was 16.6 (SD 3, max 25) and median difference score was two (interquartile range one to three). Kappa agreement for each checklist item ranged from (0.02-0.92) with an overall two-way intra-class correlation coefficient of 0.71 (95% Cl: 0.61-0.78) for comparison of overall CONSORT score between raters. Recent year of publication, increasing author number, and higher impact factor were associated with higher average CONSORT scores (p&lt;0.0001). Conclusions: Improvements in RCT reporting have been observed over time. Further work in the assessment of the inter-observer reliability of individual CONSORT items is warranted.

A Parent-Child Dyad Approach to the Assessment of Health Status and Health-Related Quality of Life in Children with Asthma

Assessment of health state and health-related quality of life (HR-QOL) are limited by a child's age and cognitive ability. Parent-proxy reports are known to differ from children's reports. Simultaneous assessment using a parent-child dyad is an alternative approach. Our objective was to assess the validity, reliability and responsiveness of a parent-child dyad approach to utility and HR-QOL assessment of paediatric asthma health states. The setting was specialist care in a hospital-based asthma clinic. Participants were 91 girls and boys with asthma aged 8 to 17 years and 91 parents. The intervention employed was parent-child dyad administration of the Health Utilities Index (HUI) 2 and 3, the Pediatric Quality of Life Inventory™ (PedsQL™) Core and Asthma modules, and the Pediatric Asthma Quality of Life Questionnaire (PAQLQ). Questionnaires were administered by interview to children and parents separately and then together as a dyad to assess the child's health state. The dyad interview was repeated at the next clinic visit. Dyad-child agreement was measured by intra-class correlation (ICC) coefficient; Spearman correlations were used to assess convergent validity. Test-retest reliability was assessed in 28 children who remained clinically stable between visits with a two-way ICC coefficient. Responsiveness to change from baseline was assessed with Spearman coefficients in 30 children who demonstrated clinical change between visits. There was no significant agreement between parent and child for the HUI2 or HUI3 whereas agreement between dyad and child was 0.55 (95% confidence interval [CI] 0.36, 0.69) for the HUI2 and 0.74 (95% CI 0.61, 0.82) for the HUI3 overall. With respect to dyad performance characteristics, both HUI2 and HUI3 overall scores demonstrated moderate convergent validity with the generic PedsQL™ Core domains (range r = 0.30-0.52; p < 0.01). Dyad HUI2 attributes demonstrated moderate convergent validity with the generic PedsQL™ Core domains of similar constructs (range r = 0.35-0.43; p < 0.001) and weaker convergent validity with disease-specific domains (range r = 0.13-0.32). Dyad HUI3 attributes demonstrated weaker convergent validity compared with the HUI2. For the assessment of test-retest reliability, significant agreement between baseline and follow-up was observed for dyad HUI2 total (r = 0.53), dyad PedsQL™ Core summary (r = 0.70) and select dyad disease-specific domains. Significant responsiveness (r > 0.4; p < 0.05) was observed for dyad HUI2 total score change over time as correlated with dyad HUI3, dyad PedsQL™ Core summary and select disease-specific domains. The parent-child dyad approach demonstrated moderate to strong performance characteristics in generic and disease-specific questionnaires suggesting it may be a valuable alternative to relying on parent proxies for assessing children's utility and HR-QOL. Future research in additional paediatric populations, younger children and a population-based sample would be useful.

Two decades of oncology randomized controlled trials: Factors associated with CONSORT clinical trial reporting checklist compliance.

6126 Background: The Consolidated Standards for Reporting Trials (CONSORT) checklist has been formulated to improve the reporting of randomized controlled trials (RCTs). The purpose of this investigation is to determine predictors of CONSORT checklist compliance in the oncology literature over the past two decades. Methods: Eight-hundred and fifty parallel two-arm RCTs assessing oncological interventions in adult breast, prostate, colorectal, and lung cancer between 1992-2010 were identified by a systematic search of the medical literature. Exclusion criteria included investigations reporting interim/secondary/long-term update analyses, pilot/phase 2 studies and studies not employing a parallel design. After full article review, 408 articles were eligible for inclusion into the CONSORT audit database. RCT descriptive variables including number of authors/study patients, 2009 journal impact factor/journal classification, type of cancer and therapeutic intervention, publication year, primary study country, and cooperative group involvement were captured for all trials. Compliance with the CONSORT checklist guidelines were assessed by two trained auditors in order to generate average and difference CONSORT checklist scores. Results: Mean average CONSORT score was 16.6 (SD 3, max 25) and median difference score was 2 (interquartile range 1-3). Kappa agreement for each individual CONSORT checklist item ranged from (0.02-0.92) with an overall two-way intraclass correlation coefficient of 0.71 (95%CI 0.61-0.78) for comparison of overall CONSORT score between raters. Recent year of publication, increasing author number, and higher impact factor were associated with higher average CONSORT scores (p<0.0001). Recent year of publication was the only factor associated with a decrease in the CONSORT difference score. Conclusions: In this largest known reported CONSORT compliance audit in the medical literature, improvements in RCT reporting has been observed over time in the cancer literature. Further work in the assessment of the reliability of individual CONSORT items is warranted given the observed kappa agreement heterogeneity.

How Many Days Are Enough? A Study of 365 Days of Pedometer Monitoring

This study was designed to determine the number of days of pedometer monitoring necessary to achieve reliable and valid estimates of a 1-year average of step counts in adults based on either consecutive days (CD) or random days (RD) of data collection. Twenty-three participants (16 women; M age = 38 years, SD = 9.9) wore a Yamax SW 200 pedometer and recorded their step counts for 365 consecutive days. Nine measurement periods of various lengths were selected (2, 3, 4, 5, 6, 7, 14, 21, and 30 days). Each measurement period was randomly selected 10 times each for CD and RD from the larger database. For reliability and validity, two-way intraclass correlation coefficients and mean absolute percentage error (MAPE) were calculated, respectively. The year-round average was considered the criterion measure of the “true” habitual physical activity. Data were analyzed separately by CD and RD. At least 5 CD or 6 RD were necessary to achieve an ICC of .80. A minimum of 30 CD or 14 RD were necessary to achieve an MAPE lower than 10%. These findings provide researchers and practitioners with useful information to determine appropriate measurement length and the method of data selection based on a desired level of reliability and validity.

How many days of pedometer monitoring? Consecutive versus random days of data collection

PURPOSE: To determine the number of days and type of data selection (consecutive vs. random) necessary to assess reliable estimates of pedometer data based on 365 days of monitoring. METHODS: Twenty-three participants (7 men, 16 women; age = 38 ± 9.9 years; BMI = 27.7 ± 6.2 kg/m2) wore a Yamax SW 200 pedometer and recorded their step counts for 365 consecutive days. Prior to data analysis, 2% missing values were identified and replaced by the average of remaining values of the person. Nine measurement periods of various lengths were selected. These were 2, 3, 4, 5, 6, 7, 14, 21 and 30 days. Each measurement period was randomly selected 10 times each for consecutive vs. random days from the larger data base. Data were analyzed separately by consecutive and random days. For consecutive days, the starting day was randomly selected from the 365 days of data for each measurement period, and for random days, all the values were randomly selected using SPSS subcommand "select cases". The two-way intraclass correlation coefficients (ICCs) were calculated for the 10 samplings of each measurement period for both consecutive and random days. The mean and standard deviation of those 10 samplings in both cases were inspected to determine the minimal number of days necessary to obtain a reliability of ICC greater than or equal to .80. RESULTS: As the length of the measurement period increased, there was an increase in the average ICC, and a decrease in standard deviation. The average ICCs were larger within consecutive days, compared to random days. The average ICCs for consecutive days ranged from .71 for 2 days to .96 for 30 days, with an average ICCs greater than .80 at 5 days (ICC = .83 ± .04). The average ICCs for random days ranged from .65 for 2 days to .96 for 30 days, with an average ICCs greater than .80 at 6 days ( ICC = .82 ± .04). CONCLUSIONS: The ICC analysis confirmed that at least 5 consecutive days or 6 random days of data collection are necessary to achieve a minimal reliability estimate of .80 in adults' pedometer data.