A new sample-size planning approach for person-specific VAR(1) studies: Predictive accuracy analysis.

Researchers increasingly study short-term dynamic processes that evolve within single individuals using N = 1 studies. The processes of interest are typically captured by fitting a VAR(1) model to the resulting data. A crucial question is how to perform sample-size planning and thus decide on the number of measurement occasions that are needed. The most popular approach is to perform a power analysis, which focuses on detecting the effects of interest. We argue that performing sample-size planning based on out-of-sample predictive accuracy yields additional important information regarding potential overfitting of the model. Predictive accuracy quantifies how well the estimated VAR(1) model will allow predicting unseen data from the same individual. We propose a new simulation-based sample-size planning method called predictive accuracy analysis (PAA), and an associated Shiny app. This approach makes use of a novel predictive accuracy metric that accounts for the multivariate nature of the prediction problem. We showcase how the values of the different VAR(1) model parameters impact power and predictive accuracy-based sample-size recommendations using simulated data sets and real data applications. The range of recommended sample sizes is smaller for predictive accuracy analysis than for power analysis.

Perceived responsiveness in suicidal ideation: An experience sampling study in psychiatric patients.

INTRODUCTION: Perceived responsiveness, or the extent to which one feels understood, validated and cared for by close others, plays a crucial role in people's well-being. Can this interpersonal process also protect people at risk? We assessed whether fluctuations in suicidal ideation were associated with fluctuations in the degree of perceived responsiveness that psychiatric patients (admitted in the context of suicide or indicating suicidal ideation) experienced in daily interactions immediately after discharge. METHODS: Fifty-seven patients reported on suicidal ideation (5 times a day) and perceived responsiveness (daily) for four consecutive weeks. The effects of established risk factors-thwarted belongingness, perceived burdensomeness, and hopelessness-were assessed as well. RESULTS: The more patients felt that close others had been responsive to them, the less suicidal ideation they reported. At low levels of thwarted belongingness, perceived burdensomeness, or hopelessness, perceived responsiveness seemed to play a protective role, negatively co-occurring with suicidal ideation. When thwarted belongingness, perceived burdensomeness, and hopelessness were high, perceived responsiveness did not have an effect. CONCLUSION: Perceived responsiveness could be a protective factor for suicidal ideation for people at risk only when they are experiencing low levels of negative perceptions. When experiencing highly negative perceptions, however, perceived responsiveness seems to matter less.