Data collector
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characteristics effect means that gender, age, ethnicity, language patterns etc. might affect the data
features collected by her/him while data collector bias refers to unconsciously distorting the data
(Frankel & Wallen, 2006). Testing effect means pre-test use in a research might contribute to the
difference between pre-and post test results due to previous practice in pre-test. History effect includes
occurrence of one or more unexpected events that are effective on the responses of the participants
during the study. As another threat, maturation effect refers to difference in responses on dependent
variable of a study due to only passing of time while attitudes of subjects include perceptions of the
participants about the study is an important factor to explain results of a study. In regression effect,
existence of extremely low and high scores in pre-testing might be closer to mean in post-testing,
hence explaining the results is confounded by these scores. As the final one, implementation threat
refers to treating experimental or implementation group in a way that gives advantage to experimental
group, so the difference between the groups might be due to additional applications and attention
(McMillian &Schumacher, 2006 p.135-138).