Screenshot of some of the actions the participants can take.

<p>If an action is still available the button is green and the action can be performed by clicking on the button. If the action is not available anymore, it is showed by a red button with the text “expired”.</p

Average points per person in the four treatments for the five days total and each day separate. The standard deviation is between brackets.

<p>Average points per person in the four treatments for the five days total and each day separate. The standard deviation is between brackets.</p

The basic information of the four treatments.

<p>The basic information of the four treatments.</p

Activities for the different levels.

<p>Activities for the different levels.</p

Stimulating Contributions to Public Goods through Information Feedback: Some Experimental Results

<div><p>In traditional public good experiments participants receive an endowment from the experimenter that can be invested in a public good or kept in a private account. In this paper we present an experimental environment where participants can invest time during five days to contribute to a public good. Participants can make contributions to a linear public good by logging into a web application and performing virtual actions. We compared four treatments, with different group sizes and information of (relative) performance of other groups. We find that information feedback about performance of other groups has a small positive effect if we control for various attributes of the groups. Moreover, we find a significant effect of the contributions of others in the group in the previous day on the number of points earned in the current day. Our results confirm that people participate more when participants in their group participate more, and are influenced by information about the relative performance of other groups.</p></div

A multilevel mixed-effects linear regression.

<p>Regression performed with the number of points that individuals collected during each day. We distinguish five models as discussed in the main text. The independent variables are the Points participants collected the previous day, group level information of the previous day (the number of Points per person, the number of chat messages, number of Likes), and dummies for the treatment participants were in. We controlled for group effects for performing a multi-level analysis where we indicated the groups participants in. The χ² was not significant which means that there was no significant group effect on the error terms. For each variable of the regression we provide the estimated value, the standard deviation (between brackets), and the 95% confidence interval.</p

Mean likes for each day.

<p>Mean number of likes per person per day divided by the number of other persons in the (sub) group.</p

Distribution of likes.

<p>Log-Log plot of the number of likes per person for the 900 participants who are ranked in other of number of likes given.</p

Text of the nightly email.

<p>Text of the nightly email.</p

Average number of messages posted per person per day for each of the four treatments.

<p>Average number of messages posted per person per day for each of the four treatments.</p