When assessing the quality of a machine, people might consider the machine’s outputs—how well it serves its function. Alternatively, people might also consider the efficiency of the machine. We investigated this possibility in two experiments (N = 392). In each experiment, participants saw pairs of machines, one with simple inside parts and one with more complex inside parts. Machines either had the same output or unknown outputs, and people judged which of the two machines was better. When the machines had the same output, participants in both experiments judged that machines with simpler inside parts were better than ones with more complex insides. However, when machines’ functions were unknown, people predominantly judged that machines with complex insides were better. Together, our work shows that people consider both parts and functions of machines when inferring quality.

People expect that others will be biased by sunk costs in their decisions. However, previous work has shown that children do not hold this same expectation. In our work, we examined whether children make other inferences about sunk costs. Specifically, we wondered whether they would anticipate that sunk costs lead others to experience negative emotions, like sadness. In two experiments, we showed children aged five to seven years (N = 168) agents who expended high- or low-costs to obtain objects that were subsequently lost or broken. We found that from around age five, children predicted that an agent will be sadder if they invested greater effort to obtain an object. We show that this expectation is not based on a simple tendency to attribute greater emotions to agents who overcame larger obstacles. Our work shows that children are not entirely insensitive to sunk costs, as previous work may have suggested.

Children are often drawn to novelty, but these preferences may depend on their goals. In two experiments (N = 302), we show that children have differing preferences for novelty when seeking information compared to when they are asked to prioritize other goals. In Experiment 1, 4-7-year-olds wanted to have typical items (e.g., a four-legged chair) and learn about atypical items (e.g., a ten-legged chair). In Experiment 2, 4-6- year-olds wanted to learn about foreign characters, but liked foreign and local characters equally. We propose that children prefer to learn about novel instances for the promise of new information, which is evident in at least two domains (artifacts and people). However, this preference diminishes when children are asked about who they like, and it reverses to a familiarity preference when choosing between artifacts to acquire. In sum, our findings suggest that children’s preferences for novelty versus familiarity are sensitive to different goals.

People tend to avoid wasting resources, but little is known about when this emerges in development. Though young children are often wasteful with food and other items, previous work suggests that children consider waste in other judgments. Here, we examined if children anticipate that others should minimize waste. In two experiments (total N = 195), children chose which of two foods someone should eat (Experiment 1; 3-7-year-olds) or two papers someone should make a snowflake with (Experiment 2; 5-year-olds). One of the options would result in minimal waste (i.e., a small food/paper) while the other would result in greater waste (i.e., a large food/paper). Children did not anticipate that others would choose smaller foods, however, at around five years they predicted that others would choose smaller paper. These findings contribute to our knowledge of the development of waste aversion and may extend our understanding of waste aversion as a form of efficiency.

Facebook sends users friend suggestions when they have friends in common with others. However, how do people actually consider mutual friendships when inferring whether two individuals are friends? We examined how people (N=352) rely on numerical factors when judging whether individuals are friends based on their mutual connections. Participants saw two target individuals and their friends within a group, and judged if the targets were friends with each other. Experiment 1 manipulated the number of mutual friends and the number of friends each target had. Experiment 2 manipulated the proportion of these two factors. People were more likely to infer friendships when I) targets had more mutual friends; II) targets had fewer friends each; and III) there was a high proportion of mutual friends, which are all factors that impact the likelihood of targets’ friendship. In sum, people consider relevant numerical information about mutual friends when making friendship judgments.

People use incomplete social network information to infer relationships. For example, if two individuals have many mutual friends, people infer they are friends with each other. We examined whether these inferences depend on domain-specific knowledge about social relationships, or instead depend on domain general-reasoning about statistics and proportions. In two experiments, participants (N=526) either saw partial information about social networks, like friendships between people, or about non-social networks, like wired connections between electrical parts. They then judged if two entities in each network were directly connected to each other. The entities varied in the number of connections and the proportion of mutual connections. People made similar judgments across social and non-social networks: with greater proportion of mutual connections, the two entities were judged as more likely to be connected to each other. In sum, inferences about networks might primarily depend on reasoning about statistics and proportions.

Adults expect others' choices will be biased by investments of effort, time, or money. However, children do not similarly consider past investments when anticipating others' actions. We examined whether prompting children about effort and emotion impacts their predictions about sunk costs. Children aged 5 to 7 years (N = 180) saw scenarios where a character collected two identical objects, one easy to obtain and the other difficult. Before children were asked which of the two objects the character will keep (sunk cost prediction), they were either asked an effort, sadness, or a control prompt. Children in the effort and sadness prompts selected the high-cost objects, suggesting they expected the character to be biased by sunk costs. However, similar to previous findings, children in the control prompt condition selected objects at chance-level. These findings suggest that if prompted, young children can anticipate others will be biased by sunk costs.