Keywords

1 Introduction

In our everyday life, the presence of others has the effect of improving the group performance of tasks, while it may also reduce an individual’s performance. The former phenomenon is called social facilitation, and the latter is called social inhibition or social loafing [2, 4, 7].

This paper focuses on how group size affects the physical performance or psychological evaluation of the participants carrying out cooperative work in a group setting. In other words, we are interested in how different numbers of other participants facilitate or inhibit interaction during the task.

A recent study on the group size effect pointed out that the difference in the number of participants, i.e., between five-person groups and ten-person groups, affected different aspects of group discussion [1]. On the other hand, a related study reported that groups perform better than individuals and that three-person groups showed better performance than two-, four- or five-person groups in a letters-to-numbers task [3]. However, few research works have analyzed both the physical performance and the psychological of the participants conducting collaborative physical tasks.

In this paper’s task, people were instructed to assemble a piece of furniture, a bed-side table, consisting of six wooden boards and fifty-four screws and other hardware. We chose this task by referring to the TV-cart assembly task [5] and the large-structure assembly task [6]. Moreover, we analyzed the task using both behavioral and psychological indexes. To this end, we investigated whether the differences in group size in the furniture assembly task inhibit or facilitate the individual’s involvement in the task.

Our research aim is to find a simple strategy of designing relationality among people from the viewpoint of the relationship between group size and the division of labor through the assembly task.

2 Method

2.1 Predictions

  • Physical performance. We predict that five-person groups will complete the task with shorter time than individuals or two-person groups because the members of five-person groups have many hands. On the other hand, the duration of interaction with materials in five-person groups will be shorter than that in individuals or two-person groups as a result of too many people being involved in the task.

  • Psychological evaluation. We predict that the members of five-person groups will feel lower degrees of contribution, satisfaction, and familiarity than the members of two-person groups because they will engage in the task for a shorter duration of interaction with the materials than the members of two-person groups.

2.2 Participants

A total of 54 graduate and undergraduate students (mean age: 20.778 years, SD: 1.449) participated in the experiment. They were randomly assigned to individuals, two-person or five-person groups. No participant was assigned a particular role in the task. Six individuals, nine two-person, and six five-person groups took part in the furniture assembly task.

2.3 Procedure

Each group was instructed to assemble the furniture as soon as possible (Fig. 1 (left)). They had to build a bed-side table, OLTEDAL of IKEA International Group, by using six boards and eight kinds of screws and other hardware, fifty-four parts totally, with an electric screwdriver according to graphical instructions (Fig. 1 (right)).

Fig. 1.
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Completed picture of a bed-side table and portion of instructions for the task of assembling furniture by using OLTEDAL of IKEA International Group

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The characteristics of the task were: (a) it took thirty-minutes by a three-person group in a preliminary experiment, (b) it required the division of roles, i.e., carrying the boards, turning the screws with the screwdriver, checking the instructions, and (c) it was difficult to explain the graphical instructions without any caption text.

2.4 Materials

We prepared a bed-side table consisting of flat wooden boards as the target object of this furniture-assembly task. Figure 2 shows the experimental materials, consisting of 6 boards, 8 kinds of screws, fasteners, and castors (54 parts in total), an electric screwdriver, and an instruction sheet.

Fig. 2.
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Materials of the task by using OLTEDAL of IKEA International Group

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Table 1. Post-experiment questionnaire on (a) contribution, (b) satisfaction and (c) familiarity
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2.5 Parameters

  • Behavioral indexes. The experimenter calculated the following individuals or group performances as behavioral indexes.

    1. 1.

      Degree of completion. Whether participants were determined to succeed in building the bed-side table or gave up building it.

    2. 2.

      TTC (Time-to-completion). The amount of time required for the furniture assembly task to be completed.

    3. 3.

      Duration of interaction with materials. The amount of time duration of interaction with the materials, i.e., the boards, the screws, the screwdriver, and the instruction, per minute for an individual, one two-person group and one five-person group.

  • Psychological indexes. The experimenter examined the results of the following questions answered on a seven-point scale through a post-experiment questionnaire.

    1. 1.

      Degree of contribution. Four questions on the participant’s degree of contribution to the task (Table 1(a)).

    2. 2.

      Degree of satisfaction. Two questions on the participant’s degree of satisfaction with the task performance (Table 1(b)).

    3. 3.

      Degree of familiarity. Eight questions on the participant’s degree of familiarity with other participants (Table 1(c)).

3 Results

3.1 Behavioral Indexes

Table 2 and Fig. 4(a) show the results of a chi-square test of the degree of completion for six individuals, nine two-person, and six five-person groups. As a result of a chi-square test, there were significant differences among individuals, two-person, and five-person groups (\(\chi ^{2}\) (2) = 8.986, p < 0.05). The results of residual analysis suggest that five-person groups succeeded in building a bed-side table, although the individuals did not succeed.

Table 2. 2\(\,\times \,\)3 contingency table for successful or unsuccessful groups among three group sizes
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Fig. 3.
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Distribution of duration of interaction with materials: an individual (upper), a two-person group (middle), and a five-person group (lower)

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Fig. 4.
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Results of behavioral indexes: (a) ratio of successful and unsuccessful groups among three group sizes, (b) time-to-completion, and (c) duration of interaction with materials per minute

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Figure 4(b) shows the results of time-to-completion (TTC) for six individuals, nine two-person groups, and six five-person groups. As a result of ANOVA, there was a significant tendency in TTC among the three group sizes (F(2) = 3.103, p = 0.07). From multiple comparisons, there are significant tendencies between individuals and five-person groups (p = 0.073). It has been suggested that five-person groups had shorter time-to-completion than individuals.

Figure 4(c) shows the results of duration of interaction with materials for a individuals, a two-person group, and a five-person group. As a result of ANOVA, there was a significant difference among the three groups (F(2) = 27.328 p = 0.002). This result suggests that the members of the individuals and two-person groups took a longer time to interact with materials than did the five-person group. Figure 3 shows the distribution of the duration of interaction with materials throughout the task.

From these results, our predictions were partly supported.

Fig. 5.
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Results of psychological indexes: (a) degrees of contribution, (b) degrees of satisfaction, and (c) degrees of familiarity

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3.2 Psychological Indexes

Figure 5 show the results of the psychological indexes, i.e., the degrees of contribution (upper), satisfaction (middle), and familiarity (lower) for nine two-person groups and six five-person groups.

Figure 5(a) shows the results of degree of contribution. As a result of the unpaired t-test, a significant difference was found in the degree of contribution to the task between two-person and five-person groups (t = 1.900, p = 0.064). This result suggests that the members of two-person groups felt a greater need to contribute to the furniture assembly task than did the members of five-person groups.

Figure 5(b) shows the results of degree of satisfaction. As a result of the unpaired t-test, there was no significant difference in the degree of satisfaction with task performance between two-person and five-person groups (t = −0.364, p = 0.718).

Figure 5(c) shows the results of degree of familiarity. As a result of the unpaired t-test, there was no significant difference in the degree of familiarity with other participants between two-person and five-person groups (t = 0.662, p = 0.512).

From these results, our predictions were partly supported.

4 Conclusion

In this study, we examined the effect of group size among individuals, two-person, and five-person groups in the furniture assembly task. From the results of behavioral indexes, a individuals was apt to give up building a bed-side table. On the other hand, both two-person and five-person groups were apt to advance toward success. Moreover, individuals and two-person groups seemed to take a longer duration to interact with materials than did five-person groups. From the results of psychological indexes, the members of two-person groups seemed to feel they made a greater contribution to the furniture assembly task than did the members of five-person groups. Considering the effect of group size in the furniture assembly task, these results suggest that social loafing effects emerged by increasing the number of participants. In other words, our results can be understood as supporting the results from the studies of both Ingham et al. and Latane et al. [2, 4].

As future work, we will analyze the behavioral indexes of more groups to test our predictions. In addition, the same experiment with other group sizes, i.e., three-person and four-person groups, should be conducted to gather findings on the most appropriate group size for the furniture assembly task. We expect these findings to help in designing relationality among people as well as between people and artifacts through the assembly task.