Complex Contagion Features without Social Reinforcement in a Model of Social Information Flow.

Contagion models are a primary lens through which we understand the spread of information over social networks. However, simple contagion models cannot reproduce the complex features observed in real-world data, leading to research on more complicated complex contagion models. A noted feature of complex contagion is social reinforcement that individuals require multiple exposures to information before they begin to spread it themselves. Here we show that the quoter model, a model of the social flow of written information over a network, displays features of complex contagion, including the weakness of long ties and that increased density inhibits rather than promotes information flow. Interestingly, the quoter model exhibits these features despite having no explicit social reinforcement mechanism, unlike complex contagion models. Our results highlight the need to complement contagion models with an information-theoretic view of information spreading to better understand how network properties affect information flow and what are the most necessary ingredients when modeling social behavior.

Impact of COVID-19 Controls on the Use of Illicit Drugs and Alcohol in Australia.

Methamphetamine, MDMA, cocaine, cannabis, and alcohol in samples from 20 wastewater treatment plants servicing the eight state or territory capitals of Australia were analyzed, with equivalent coverage of >45% of the national population. Trends in drug consumption were calculated and assessed from samples collected from 2016 to 2020, with a focus on pre-COVID-19 (August 2016 to December 2019), versus February to June 2020, when Australia observed a nationwide lockdown. Results showed delayed but significant decreases in methamphetamine, >50% in Western Australia. In contrast, significant increases in cannabis in most jurisdictions were observed. This suggests changes in consumption may be somewhat linked to reduced supply of imported substances, with increased use of locally produced drugs. Initial decreases in cocaine and MDMA consumption were evident in many parts of the country, but pre-COVID trends were re-established after April 2020. Interestingly, weekend-weekday differences were narrowed for cocaine, MDMA, and alcohol during lockdown, which might be expected due to bars being closed and social gathering not allowed. With this study providing insight into the first four months of COVID-19 restrictions in Australia, it remains to be seen what the longer-term effect of the pandemic will be.