nonsystematic

/ˌnɑnsɪstəˈmætɪk/
adjective
  1. Not done or organized according to a fixed plan or method; lacking a consistent system.
    • The researcher's nonsystematic data collection made the results unreliable.
    • His nonsystematic approach to cleaning meant he often missed the same spots.
    • She preferred a nonsystematic way of learning, jumping from topic to topic.