STRUCTURAL BREAKS AND VOLATILITY SHIFTS IN MONTHLY MALARIA CASE COUNTS AT FMC ASABA,NIGERIA: A TIME-SERIES ANALYSIS, 2010–2022

Facility-level malaria records can reveal operational changes that annual  summaries may miss. This study analysed de-identified monthly outpatient malaria counts from Federal Medical Centre (FMC) Asaba, Nigeria, January 2010–December 2022. After auditing the records, a continuous panel of 156 months was analysed; 147 months were observed and nine missing months were linearly imputed. The total series was log-transformed, decomposed by STL, tested for stationarity, and evaluated with CUSUM, BIC-selected segmented regression, Brown-Forsythe variance tests, ARCH- LM diagnostics, and subgroup break searches. Monthly total counts ranged from 107 to 1,829 (mean = 606.55). Three mean-level breaks were retained: October 2013, June 2015, and June 2019. Mean counts declined from 650.42 to 320.52 across the first three regimes, then rose to 962.23 after June 2019. Residual volatility increased after April 2021. These statistical shifts support break-sensitive facility surveillance, while not identifying causal drivers.