Suicide Seasonality: Complex Demodulation as a Novel Approach in Epidemiologic Analysis

Abstract

BackgroundSeasonality of suicides is well-known and nearly ubiquitous, but recent evidence showed inconsistent patterns of decreasing or increasing seasonality in different countries. Furthermore, strength of seasonality was hypothesized to be associated with suicide prevalence. This study aimed at pointing out methodological difficulties in examining changes in suicide seasonality.Methododology/Principal FindingsThe present study examines the hypothesis of decreasing seasonality with a superior method that allows continuous modeling of seasonality. Suicides in Austria (1970–2008, N = 67,741) were analyzed with complex demodulation, a local (point-in-time specific) version of harmonic analysis. This avoids the need to arbitrarily split the time series, as is common practice in the field of suicide seasonality research, and facilitates incorporating the association with suicide prevalence. Regression models were used to assess time trends and association of amplitude and absolute suicide numbers. Results showed that strength of seasonality was associated with absolute suicide numbers, and that strength of seasonality was stable during the study period when this association was taken into account.Conclusion/SignificanceContinuous modeling of suicide seasonality with complex demodulation avoids spurious findings that can result when time series are segmented and analyzed piecewise or when the association with suicide prevalence is disregarded.

Chris Cornell, the Black Hole Sun, and the Seasonality of Suicide

“…Goodwin and Jamison [7] reviewed 61 studies in the northern hemisphere and found a striking May peak in suicides and a less common, smaller bimodal October peak. Since the review of Goodwin and Jamison [7], there have been dozens of additional studies that have replicated consistent late spring peaks in suicide in nearly all of the largest datasets, including in the northern hemisphere (in those studies that reported both a monthly peak and a total n for suicides), the USA (May; n = 649,843, the present study), Japan (April; n = 501,950 [29]), Sweden (May; n = 161,182 [30]), Italy (May; n = 141,180 [31]), Finland (May; n = 96,159 [30]), England (January; n = 92,909 [32]), Austria (May; n = 67,741 [33]), Mexico (May; n = 64,298 [34]), Spain (July; n = 42,905 [35]), Denmark (May; n = 37,987 [36]), Switzerland (May/June; n = 37,518 [37]), Norway (May; n = 20,156 [38]), China (May; n = 14,450 [39]), and Ireland (April; n = 7,899 [40]). In the southern hemisphere, reciprocal spring peaks have been found in Australia (November; n = 57,936 [41]), South Africa (October; n = 16,389 [42]), and São Paulo, Brazil (November; n = 6,916 [43]).…”

“…Statistically significant increases in the amplitude of the seasonal suicide rhythm have also been found in Ireland (1980–2000) [40] and Australia (1970–1999) [41]. By contrast, the amplitude of the seasonal suicide rhythm did not change significantly in either Austria (1970–2008) [33] or China (1991–2009) [39], whereas in Norway (1969–2007) [38] and possibly Slovenia (1971–2002) [45] the amplitude decreased significantly. Clearly, the factors that contribute to these disparate temporal variations in the amplitude of the seasonal suicide risk factor are of great interest [8].…”

The Mexican Cycle of Suicide: A National Analysis of Seasonality, 2000-2013

“…This analytical technique can improve the characterization of the seasonality of suicide as well as increase knowledge about the processes leading up to it and the potential influences of temporary exogenous changes. While this technique has been used in other countries to analyze suicides [ 25 ], this is the first investigation of this type in Mexico. Therefore, the aim of the present analysis is to explore the seasonal behavior of suicide in Mexico using spectral decompensation and extensively characterize all the cases occurring at the national level between the years 2000 and 2013.…”

Einfluss von natürlichen Lithiumsalzvorkommen auf die Suizidmortalität in Chile 2000–2009: Eine geographische Analyse

“…Es scheint plausibel, dass die niedrigere saisonale Variabilität der Suizidmortalität im Norden Chiles auch dem bekannten stimmungsstabilisierenden und antisuizidalen Effekt von Lithium geschuldet sein könnte [16]. Allerdings muss in Betracht gezogen werden, dass die Amplituden suizidaler Saisonalität in Regionen mit niedrigen Suizidraten aus statistischen Gründen eher gering sind -wie schon in der Literatur beschrieben [34].…”