TY - CONF A1 - Nakov, Preslav A1 - Da San Martino, Giovanni A1 - Elsayed, Tamer A1 - Barrón-Cedeño, Alberto A1 - Míguez, Rubén A1 - Shaar, Shaden A1 - Alam, Firoj A1 - Haouari, Fatima A1 - Hasanain, Maram A1 - Mansour, Watheq A1 - Hamdan, Bayan A1 - Sheikh Ali, Zien A1 - Babulkov, Nikolay A1 - Nikolov, Alex A1 - Koshore Shahi, Gautam A1 - Struß, Julia Maria A1 - Mandl, Thomas A1 - Kutlu, Mucahid A1 - Selim Kartal, Yavuz T1 - Overview of the CLEF–2021 CheckThat! Lab on Detecting Check-Worthy Claims, Previously Fact-Checked Claims, and Fake News T2 - Experimental IR Meets Multilinguality, Multimodality, and Interaction N2 - We describe the fourth edition of the CheckThat! Lab, part of the 2021 Conference and Labs of the Evaluation Forum (CLEF). The lab evaluates technology supporting tasks related to factuality, and covers Arabic, Bulgarian, English, Spanish, and Turkish. Task 1 asks to predict which posts in a Twitter stream are worth fact-checking, focusing on COVID-19 and politics (in all five languages). Task 2 asks to determine whether a claim in a tweet can be verified using a set of previously fact-checked claims (in Arabic and English). Task 3 asks to predict the veracity of a news article and its topical domain (in English). The evaluation is based on mean average precision or precision at rank k for the ranking tasks, and macro-F1 for the classification tasks. This was the most popular CLEF-2021 lab in terms of team registrations: 132 teams. Nearly one-third of them participated: 15, 5, and 25 teams submitted official runs for tasks 1, 2, and 3, respectively. KW - Fact-checking KW - Check-worthiness estimation KW - Desinformation KW - Fehlinformation Y1 - 2022 UR - https://opus4.kobv.de/opus4-fhpotsdam/frontdoor/index/index/docId/2602 SN - 978-3-030-85251-1 SP - 264 EP - 291 PB - Springer CY - Cham ER -