18356
Participants completed Web - based assessments of pre - 9 / 11 mental health , acute stress 9 - 23days after 9 / 11 , the quality of social environments 1year post - 9 / 11 , economic stress 18months post - 9 / 11 , and PTS symptoms and impaired functioning 2 and 3years post - 9 / 11 .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None