We follow the COSMIN (Consensus-Based Standards for the Selection of Health Status Measurement Instruments) standard, which is the consensus-based checklist for the preferred design characteristics and statistical methods of studies on measurement properties [17].

This research follows a test-retest design with crossover. The participants were randomly matched into 2 groups. Data for BBT and dBBT were collected at 2 measurement time points, with crossover after the first measurement point. The total data collection period was 10 days.

A total of 2 testers (raters 1 and 2) conducted all data collection. Before the study, the 2 testers performed 2 pretests.

The BBT was developed by Jean Ayres and Patricia Buehler in 1957 and modified to the current version by Patricia Buehler and Elizabeth Fuchs in 1976. Normative data for children and adults were established in 1985 [8,9].

The BBT is a widely used outcome measure to quantify upper limb motor function, especially gross manual dexterity [6]. The BBT comprises a wooden box (53.7 cm×25.4 cm×8.5 cm) that is divided into 2 compartments (25.4 cm each) by a partition and 150 blocks (cubes with 2.5 cm side length) in 1 of the 2 boxes [9]. Participants have to move the blocks one by one from 1 compartment of a box to another in 60 seconds. The BBT is timed with a stopwatch, and after 60 seconds, the transported blocks (on average 75-90 for healthy persons) are to be counted by the test administrator. A 15-second trial period is permitted at the beginning of the test.

The digital version of the BBT, the dBBT, is quite similar to the BBT but uses digital measurements. We have developed the dBBT to further standardize the measurement with the BBT by using digital functions to automatically measure the time and the achieved scores. Figure 1 shows an overview of the dBBT. The dBBT consists of the control unit and the test box with a partition. The test box is in form and dimensions oriented to the specifications of Mathiowetz et al [9]. The dBBT and the blocks were created using a 3D printer. Load cells are installed in the bottom of the 2 boxes to record the number of blocks automatically. A microcontroller in the control unit processes the sensor signals, automatically measuring the test time, and controls the user inputs through the buttons and the output through the display.

On the control unit, the start button starts the timing, and the LEDs on the partition light up green until the test time is over; then they light up red. The dBBT automatically counts the valid blocks (if 2 blocks are transported at the same time, the system counts only 1 block for the valid result) and shows the achieved score (number of blocks in 60 seconds) on the display. Also, the 15-second trial period is provided by the dBBT.

The prototype of the dBBT enables the assessment according to the standardized specifications of Mathiowetz et al [9].

Participants were occupational therapy students at the University of Applied Sciences in Vienna (Austria). The sample size calculation for evaluating correlation was calculated with G*Power Version 3.1.9.7 (Heinrich-Heine-University Düsseldorf). The calculation with the factors correlation point biserial model, 2 tails, effect size 0.5 [18,19], α error .05, and power 0.85 [20] resulted in a sample size of 26. Participants were recruited in the fall of 2022 through a presentation of the study in collaboration with a faculty member in the program. The inclusion criteria were (1) individuals without a history of neuromuscular or orthopedic dysfunction that would significantly affect dexterity and (2) 18 years or older. Handedness was identified by asking the participant which hand was used for writing. In total, 32 people participated in this study.

We used SPSS Statistics (version 28.0; IBM Corp) for data analysis. Descriptive statistics were used to describe the study population. The normality of the data was evaluated using the Shapiro-Wilk test. Concurrent validity was determined by the Pearson correlation coefficient (r) for the relationship between the conventional BBT and the dBBT at measurement point 1. The correlation was classified as follows: no or very low, r=0-0.25; low, r=0.26-0.40; moderate, r=0.41-0.69; high, r=0.70-0.89; and very high, r=0.90-1.0 [20]. The level of statistical significance was set at P≤.05.

The agreement between the BBT and dBBT was examined using the Bland-Altman analysis to check for systematic bias and estimate the limit of agreement (LOA) [20,21]. In the Bland-Altman scatter plot, the x-axis represents the mean of these measurements, and the y-axis shows the difference between the 2 paired measurements. The fixed bias was statistically evaluated using the 95% CI of the mean differences between the BBT and dBBT values. A fixed bias is present when 0 is not within the range of the CI. After ensuring that the differences are normally distributed, SD can be used for defining the LOA mean (SD 1.96) [22]. LOAs show how much the scores can vary in stable patients. A change in scores within LOAs or smaller indicates a measurement error; outside the LOAs, it can be assumed that these are statistically significant changes [20].

For assessing interrater and test-retest reliability, intraclass correlation coefficients (ICC) were used. To estimate the correlation, the following classification of correlation was used [23]: less than 0.5 poor, between 0.5-0.75 moderate, between 0.75-0.9 good, and greater than 0.9 excellent. Measurement error was determined by estimating the standard error of measurement (SEM) using the formula , where SD is the standard deviation of the means from all probands [20] of the test-retest scores and ICC from the test-retest reliability. Smallest detectable change (SDC) was calculated, based on the test-retest parameter SEM, as follows: [20]. The SDC represents an absolute measure of reliability (measurement error) and is used to assist in interpreting results and determining whether a change between repeated tests is a random variation or a true change in performance [24].

In the data set, outliers became apparent after data collection during the initial data analysis. These outliers showed up in differences in the measurement repetitions. Values with more than 20% (above the 90th percentile) difference between 2 measurements cannot be assigned to any natural variance in healthy persons. As the participants were all individuals with unrestricted hand function, a true outlier can be ruled out. A possible reason is seen as an error in the test execution or data collection. Therefore, 3 corresponding data sets from a total of 32 participants were excluded from further analysis. The sample size of the assessed data was thus 29.

The study design includes 2 measurement time points. The test procedures took place in a room specially prepared for this purpose at the University of Applied Sciences Campus Vienna. The setting and test instructions for the BBT and the dBBT corresponded to the standard set by Mathiowetz et al [9]. The test instructions were translated into German by the author. One measurement of the writing hand of each participant was performed. Participants sat on a chair in front of a table. The test box was centrally located in front of them. The box with the blocks was on the side of the hand to be tested. The instructions for the test were read out by the tester according to the standardized instructions, including a short demonstration. The participants performed a 15-second trial period before the recorded test. For the start, the participants have to position their hands on the left and right sides of the box; then the start signal is given, and the timing starts [9]. The tests were timed at the BBT with a stopwatch and at the dBBT with the implemented time measurement at the push of a button. If the participant transports several blocks at the same time, only one is counted. If a block has fallen from the table, the participant should not be distracted by it and continue with the task. If the block was already transported over the partition before it fell down, it will be counted in the result [9].

Data collection took place at 2 measurement times, with 10 days in between. This period was chosen to be small enough so that no change in hand function occurs, but at the same time large enough to minimize influences from practice or memory [18,25]. A total of 29 participants were randomized into both groups, resulting in 14 participants in group 1 and 15 in group 2. At the first measurement, group 1 was tested from tester 1 with the dBBT, and then on the same day using the conventional BBT. Group 2 was tested by tester 2 in reverse order (first the conventional BBT, and then the dBBT).

At the second measurement point, 10 days after the first measurement, a total of 15 participants took part. Both groups were tested using the dBBT. Here, both groups changed the tester: group 1 was thus tested by tester 2 and group 2 by tester 1.

This study design was chosen to allow assessing both test-retest reliability and interrater reliability as well as the validity of the dBBT compared with the BBT.

The study protocol was in accordance with the Declaration of Helsinki and was approved by the ethics committee (EK Nr 97/2022) of the University of Applied Sciences Campus Vienna. This study has been registered on the Open Science Framework [26].

The characteristics of the healthy participants who participated in this study are summarized in Table 1. The mean age of the participants was 23.5 (SD 5.2) years. The majority of the participants (n=28) were female and right-handed.

The second measurement point was completed by 15 probands. Table 2 shows the means, SDs, maximum and minimum scores, and the number of valid values of the 3 measurements with the BBT, dBBT1 (both at the first measurement time point), and dBBT2 (at the second measurement time point). The BBT shows on average a few higher scores than the dBBT1 and dBBT2. The average score ranges (blocks in 60 seconds) are 81.83 for the BBT, 76.86 for the dBBT1, and 80.71 for the dBBT2.

A Pearson correlation analysis was performed to determine if there was a correlation between the variables BBT and dBBT1 and between BBT and dBBT2.

Our examination of BBT and dBBT1 (n=29) showed that BBT had higher scores (mean 81.83, SD 6.35) than dBBT1 (mean 76.86, SD 4.98) and dBBT2 (mean 80.71, SD 7.75). There was a moderate correlation of r=0.48 between the variables BBT and dBBT1. The result of the Pearson correlation analysis showed that there was a significant relationship between BBT and dBBT1 (r₂₉=0.48, P=.008).

A dependent samples t test showed that the difference between the scores of BBT and dBBT1 was statistically significant (t₂₈=−4.96, P<.001; 95% CI −7.21 to −2.72).

The Bland-Altman plot to evaluate the agreement between BBT and dBBT1 is shown in Figure 2. The fixed bias was statistically evaluated using the 95% CI (SE 1.96) of the mean differences between the BBT and dBBT values. For BBT and dBBT1, the mean difference was 4.97 (7.11-2.82), and a fixed bias was present.

All obtained values of BBT and dBBT1 (except one) were in the range of the LOAs (16.69 to −6.59), which indicates a sufficient agreement between the 2 measurement methods.

For the calculation, the scores of the dBBT (blocks in 60 seconds) were compared at the 2 measurement points within a 10-day interval. From the whole sample of 29 healthy participants, 15 completed the second measurement. A total of 14 participants did not attend the second measurement point without giving a reason. The test-retest reliability for these 15 participants was determined by calculating the ICC (3,k) based on the 2-way mixed model (k fixed raters are defined), absolute agreement (agreement between 2 raters is of interest), and average measure [20,27]. The ICC is moderate, with an ICC of 0.72 (−0.23 to 0.93; P<.001). Because the ICC is only an expected value of the true ICC, it is appropriate to assess the degree of reliability on the basis of the 95% CI of the ICC value and not the ICC value itself [23]. The value 0 is included in the CI 95% range, indicating that the correlation is not statistically significant.

An SEM of 3.1 blocks was identified, which represented 3.88% of the mean score observed in the test-retest session.

The SDC was 8.5 blocks (10.77%); 95% of the tested population had a random variation of less than 8.5 blocks on repeated testing, and a value above would indicate a true change beyond an expected measurement error. An SDC% <10% is considered to indicate an excellent random measurement error [3]. The SDC% (10.77%) of the dBBT indicates that the dBBT is capable of supporting clinicians in assessing the significance of outcomes and interpreting treatment efficacy.

Interrater reliability was assessed with ICC (2,k), based on the 2-way mixed and consistency model [20,27]. For this purpose, the results of tester 1 and tester 2 were compared for the 15 participants who completed the dBBT at both measurement points. The calculated interrater reliability was moderate, with an ICC of 0.67 (0.02-0.89; P=.23) and was statistically significant. The result was close to the limit of high interrater reliability, which is 0.7 [18].

The aim of this study was to evaluate the concurrent validity, the test-retest reliability, and the interrater reliability of the newly developed dBBT.

Previous studies have presented various further developments of BBT assessments, such as the conventional BBT extended with additional technologies [10-13,28]. Other works have also investigated the BBT using virtual reality [14-16,29]. Compared with these BBT implementations, our new dBBT is unique because no additional technical equipment is required. It is a stand-alone solution, like the conventional BBT, and therefore does not require any additional skills from the test administrator or proband. At the same time, it offers digital functions that support the execution of the measurement (collection of time and result).

On the whole, participants moved fewer blocks with the dBBT1 (mean 76.86, SD 4.98) and the dBBT2 (mean 80.71, SD 7.75) than in the original BBT (mean 81.83, SD 6.35).

The comparison of the new dBBT with the original BBT found a moderate correlation between the BBT and dBBT (r₂₉=0.48, P=.008). These results are comparable to Everard et al [4], who reported a correlation of r=0.58 (P<.01) for healthy people who completed hand dexterity measurement with the BBT and a virtual reality version of the BBT.

The scores of dBBT1 were significantly lower than the scores of BBT measurements (t₂₈=−4.96, P<.001; 95% CI −7.21 to −2.72).

The Bland-Altman plot showed that the dBBT1 achieved, on average, 4.97 fewer blocks than the measurement with the BBT. As the value 0 is not in the 95% CI of the mean (7.11-2.82), a fixed bias is assumed. All but one of the values collected fell within the LOAs (16.69 to −6.59), indicating that the dBBT has sufficient accuracy to provide an accurate measure of hand dexterity.

The test-retest reliability, ICC (3,k), of the 2 dBBT sessions (n=15) was moderate, with an ICC of 0.72 (−0.23 to 0.93; P<.001), in healthy adults. A comparable study by Everard et al [4] reported ICC values of 0.7 to 0.9.

The SEM calculated for the dBBT was 3 blocks. SDC, useful for interpretation of real changes in hand dexterity, was 8.5 blocks (10.77%) for dBBT.

The ICC value indicates what proportion of the total variance over a range of values is due to heterogeneity among study participants [30]. In this study, only healthy participants of mainly similar age were tested. A lack of variance among the participants may result in a lower ICC value [20].

The examination of interrater reliability showed a moderate ICC of 0.67 (0.02-0.89; P=.23). In contrast, in the study by Mathiowetz et al [9], a high interrater reliability (r=0.85-0.99) was reported. However, this study is not directly comparable because the calculations were made using the Pearson correlation coefficient, which is no longer considered contemporary [17,20]. Platz et al [31] also showed high interrater reliability with an ICC>0.9.

It should be noted in this interrater reliability result that the sample has low variances, which may lead to a low ICC value [20].

The BBT is suitable for use in clinical settings. It measures the dexterity performance of the hand. The BBT is particularly recommended for progress measurements of patients with neurological disorders [32]. The BBT is mainly used to assess therapy effects, that is, a measurement is taken at the beginning of a defined period and a repetition at the end. The assessment of a possible therapy effect is solely based on the comparison of these 2 measurements. Therefore, the fact that the dBBT measures on average 5 blocks less than the original does not affect its suitability as a measurement tool. It does not affect the ability of the dBBT to assess a possible therapeutic effect.

The dBBT shows moderate results in test-retest and interrater reliability. The dBBT enables compliance with the standardized measurement protocol, according to Mathiowetz et al [9]. It automatically measures the test time, counts the transported blocks, and shows the achieved result on a display. These functions help to increase objectivity. The material (plastic) is well suited for clinical use, compared with the original, which is made of wood. The shape of the dBBT is similar to the BBT, so it is just as easy for clinicians to transport and use.

In the next step, the practicability of the dBBT will be investigated in qualitative studies in order to be able to make statements about its clinical utility. After that, studies are planned with populations that typically use the BBT, with people after stroke and people with multiple sclerosis. These steps, which follow this study, will make it possible to make statements about the generalizability of the results.

The study was conducted with healthy individuals without hand dexterity limitations. Therefore, the results need to be confirmed in future studies in patients with hand dexterity impairments.

In this study, the results of hand dexterity measurements from 2 measurement time points were collected and compared. From the authors’ point of view, the fact that the majority of the participants were female had no influence on the present results.

The sample size was calculated to be sufficient for group comparisons according to our power analysis. However, at the second measurement time point, only 15 people participated, which could affect the strength of the calculations for test-retest reliability and interrater reliability.

The homogeneity of the participant group could also have an influence on the results.

This study showed that the newly developed dBBT is a valid, reliable, and usable tool to assess manual dexterity among healthy participants. The dBBT provides automatic timing and counting to help further objectify the results of hand dexterity measurement.