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For example , airflow obstruction in diagnosed asthma patients showed little worsening over time in one study ( Burrows , Barbee et al ., 1991 ) , but it worsened at an excessive rate with increasing age in another study ( Peat et al ., 1987 ) . The phytotoxic effects of acute ozone exposure , that is , the episodes of relatively high concentrations of ozone for a few days , are manifest as a relatively rapid decrease in photosynthetic rates and stomatal closure in wheat ( Farage et al ., 1991 ) . Here again , formation of ductile shear zones localized late fluid flow , with the most intense alteration occurring in the ductile faults ( Dick , Meyer , et al ., 1991 ) . Focus group research on the modules involved the following tasks : to evaluate the comprehensibility of the questions , the cognitive processes of respondents , and quality and type of information that is obtained from questions ; and to revise questions and order of questions within the modules and the core questionnaire ( Willis et al ., 1991 ) . A prospective study in Indonesia ( Pariani et al ., 1991 ) showed that discontinuation can be related to contraceptive choice .