'Not finding causal effect' is not 'finding no causal effect' of school closure on COVID-19.

Similarly, the untreated group may tend to include municipalities (with 100 incidents per unit before 7 days) when there is a decreasing trend.

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In this situation, if the treatment (school closure) decision-making was affected by the increasing/decreasing trend, the treated group may tend to include municipalities (with 100 incidents per unit before 7 days) when there is an increasing trend.

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ATC estimates also yielded similarly insignificant/barely significant patterns ( Figure 3 ).

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