STATUS: ---------- Submitted for review in Journal of Open Psychology Data --- *Authors* **Heino, Matti Toivo Juhani** (University of Helsinki) **Abstract** ---------- Recent discussions on threats of group-to-individual generalisability in psychology have prompted the need for individual-level data that is of sufficient length, in order to study within-individual psychological processes. In the current study, a single participant monitored their own cognitive dynamics daily before and after a 20-minute meditation session delivered by a mobile application. Over the course of 900 days, the participant performed Stroop tests and self-reported variables regarding cognitions (e.g. mood, clarity, calm, tiredness) as well as context (e.g. sleep, fasting, coffee, self-regulation). *Keywords* N-of-1; Stroop; meditation; fasting; sleep; self-regulation *Context* The author collected their own data independently. *Collection Dates* 1.7.2014 - 22.12.2016 **Background** ---------- As most of psychology involves so-called non-ergodic processes, large-sample research cannot provide reliable information about individual-level processes [1–3]. In addition, psychological phenomena are often non-linear, and time series can display long-range correlations as well as fractal scaling [4–6]. Hence, individual-level data of sufficient length is required to study psychological processes. **Methods** ----------- **Sample** Participant, who is also the author, was a 33-year-old male doctoral student, who collected the data independently. Data is missing from ca. yearly week-long conference visits and meditation retreats, including one month-long retreat. Variables were added during the course of the study; e.g. Stroop test results are available from 718 days (performed twice daily). **Materials** Stroop test used was an online version available at www.onlinestrooptest.com. Guided meditations from www.headspace.com depicted different monthly themes (“packages”) and the instructions varied each day. Participant logged the data in a spreadsheet, which also contained a script to randomise the meditation posture (i.e. sitting, walking or standing). **Procedures** Each day, at their convenience and when a computer was available, the participant logged in the cognitive and contextual variables before performing a Stroop test. Immediately after this, they performed a 20-minute guided meditation, directly after which they re-did the Stroop test. After logging the Stroop test results in a spreadsheet, they logged in post-meditation reports of the cognitive variables as well as additional contextual variables such as whether they were suffering from after-effects of drinking alcohol, or had experienced a self-regulation failure on the current day. **Quality Control** Location of data collection was mostly at home, but occasionally elsewhere (nearly exclusively at the office); this is indicated in the data. The data also indicates when the quality of the data point has potentially been compromised, e.g. due to disturbations mid-session. Extensive qualitative diary entries concerning the setting, relevant events having taken place pre-session, as well as data collection notes, are available by request, but not shared due to privacy concerns. **Ethical issues** This study was initiated and performed by the author, who provided informed consent. Qualitative diary entries are removed from the data. **Data Collectors** MH from University of Helsinki devised the study and collected the data (including acting as the participant). **Reuse potential** This dataset can be used by researchers interested in cognitive dynamics, or the effect of sleep, (intermittent) fasting, or coffee (abstinence) on those dynamics. Methodologists may also be interested in studying long-term learning effects in the Stroop task. Due to the length of data, it is possible to explore non-linear scaling and perform fractal analyses. Data can also be used in teaching N-of-1 analysis methods, e.g. in relation to studying self-regulation. References ----------  Fisher AJ, Medaglia JD, Jeronimus BF. Lack of group-to-individual generalizability is a threat to human subjects research. PNAS 2018:201711978. https://doi.org/10.1073/pnas.1711978115.  Hamaker EL. Why researchers should think “within-person”: A paradigmatic rationale. 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