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# Project Overview This project is hosted on the [Many Lab][1]. Through this network, we recruited a total of 12 labs from all over the world, including Germany, the USA, the UK, Poland, Sri Lanka, Russia, and Serbia. Originally, we had included only one study. Because more sites than expected participate, we have split the sites in data collection for two studies. The description of the original study can be found [here][2], and a description of the follow up study can be found in the '[follow-up][3]' section. #### 1. What is the project? In these two studies we investigate the relationship between co-sleeping and sugar and fat intake in Study 1, and with self-control and self-esteem in Study 2. Part of this project is a preregistered, confirmatory test of the effect that we have previously detected. Thus, in these two follow up studies, we try to confirm this effect, then try to find out what accounts for these sex differences, and, finally, try to find out consequences of co-sleeping on self-control and self-esteem, which could be indicative of attachment-like, exploratory behaviors. In both studies however we first build the model and explore the dataset by splitting the sample, after which we confirm in the other half of the sample. In our first, pilot, study we found that co-sleeping (versus alone sleeping) led to decreased glucose intake the following day (but this only worked for males). The study is conducted across labs, to 1) increase the sample size and 2) investigate its generalizability across contexts and cultures. In both the first and the second study we will do so by means of a set of questionnaires, which will consist of a list on demographics, sleeping practices, Attachment Style, a subscale of the Center for Epidemiologic Studies Depression Scale (CES-D), a subscale of the Multidimensional Assessment of Interoceptive Awareness Scale ([MAIA][4]), the Communal Strength Scale (CSS; [Mills et al., 2004][5]), a Social Network Index (SNI; [Cohen et al., 1997][6]) (only used in the first study), and a questionnaire on sugar intake and fat consumption. A full overview of the questionnaires used in study 1 can be found [here][7]. In our second study, we will replace the Social Network Index questionnaire by a set of questions on exercise, one on self-control ([Tangney, Baumeister & Boone, 2004)][8] and and a question on self-esteem [Robins, Hendin & Trzesniewski, 2001][9]. A full overview of the questions of the second study can be found [here][10]. #### 2. What is expected from each collaborator? Each collaborating lab must, ater having been in contact with Lotje Hogerzeil, and having been assigned to either Study 1 or 2: • Translate, backtranslate survey materials and check the original and backtranslation for loyalty of meaning for non-English sites. The document to be translated for the first study can be found [here][11]. The document for the second study can be found [here][12]. • Recruit at least 120 participants (150 being the ideal). This number is based on a G*power calculation with α=0.05, power of .80, effect size of .21 (based on the interaction effect between co-sleeping and gender of our previous study), which brought us to a minimum of 196 participants * for the entire sample *. This number should be overshot slightly, as we do not know how many co-sleepers will be among them; thus, we aimed for 250 participants at least for the entire sample. We required collaborating labs to recruit at least half of this number. Given the current amount of labs, we will easily overshoot this number in both studies. • Check the local temperature of the day the participant took part, based on the participant's IP address, based on a reliable local weather base. • If a participant pool isn't used, identify a payment system (funding is not provided by the project). • Since the survey can be taken at home by participants via an emailed link, no lab space or computers will be needed. • An e-mail Lotje Hogerzeil ( and Hans IJzerman ( in case an IRB submission is needed, and also when it is not needed. Without an email that explains IRB rules to the project team, the project cannot be started. #### 3. What will collaborators get out of this? The lead authors (Lotje Hogerzeil, Nicole Legate, and Hans IJzerman) will write up the paper, but will obviously send around drafts for comments/revisions. Author order in publication will be: lead author (Lotje Hogerzeil), second author (Nicole Legate), and then collaborating researchers (ordered alphabetically). Hans IJzerman will be listed as final author. If collaborators fail to hit the 125-person minimum, but still provide usable data, then they will still be on the paper, but will be demoted in the authorship order. If they provide no usable data, then they will be dropped from the paper. #### 4. How do I join this project? E-mail Lotje Hogerzeil ( to join this project. Before committing, review the Project Timeline to make sure that you will be able to meet the project goals. [1]: "Many Lab" [2]: [3]: [4]: [5]: [6]: [7]: [8]: [9]: [10]: [11]: [12]:
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