IDEAS home Printed from
   My bibliography  Save this paper

A derivation of the optimal answer-copying index and some applications


  • Mauricio Romero


  • Álvaro Riascos


  • Diego Jara


Multiple choice exams are frequently used as an efficient and objective instrument to evaluate knowledge. Nevertheless, they are more vulnerable to answer-copying than tests based on open questions. Several statistical tests (known as indices) have been proposed to detect cheating but to the best of our knowledge they all lack a mathematical support that guarantees optimality in any sense. This work aims at filling this void by deriving the uniform most powerful (UMP) test assuming the response distribution is known. In practice we must estimate a behavioral model that yields a response distribution for each question. We calculate the empirical type-I and type-II error rates for several indices, that assume different behavioral models, using simulations based on real data from twelve nation wide multiple choice exams taken by 5th and 9th graders in Colombia. We find that the index with the highest power among those studied, subject to the restriction of preserving the type-I error, is the one that uses a nominal response model for item answering, conditions on the answers of the individual suspected of being the source of copy and calculates critical values via a normal approximation. This index was first studied by Wollack (1997) and later by W. Van der Linden and Sotaridona (2006) and is superior to the indices studied and developed by Wesolowsky (2000) and Frary, Tideman, and Watts (1977). Furthermore, we compare the performance of the indices on examination rooms with different levels of proctoring and find that increasing the level of proctoring can reduce copying by as much as 50% and that simple strategies such as having different students answer different portions of the test at different times canal so reduce cheating by over 50%. Finally, a Bonferroni type false discovery rate procedure is used to detect massive cheating. The application is straightforward and we believe it could be use to make entire examination rooms retake an exam under stricter surveillance conditions.

Suggested Citation

  • Mauricio Romero & Álvaro Riascos & Diego Jara, 2014. "A derivation of the optimal answer-copying index and some applications," DOCUMENTOS CEDE 012061, UNIVERSIDAD DE LOS ANDES-CEDE.
  • Handle: RePEc:col:000089:012061

    Download full text from publisher

    File URL:
    Download Restriction: no

    References listed on IDEAS

    1. George Wesolowsky, 2000. "Detecting excessive similarity in answers on multiple choice exams," Journal of Applied Statistics, Taylor & Francis Journals, vol. 27(7), pages 909-921.
    2. Diego Jara & Álvaro Riascos & Mauricio Romero, 2010. "Detección de copia en pruebas del Estado," DOCUMENTOS CEDE 007093, UNIVERSIDAD DE LOS ANDES-CEDE.
    3. Alexander Shapiro & Jos Berge, 2002. "Statistical inference of minimum rank factor analysis," Psychometrika, Springer;The Psychometric Society, vol. 67(1), pages 79-94, March.
    Full references (including those not matched with items on IDEAS)

    More about this item


    : Index; Answer Copying; False Discovery Rate; Neyman-Pearson Lemma;

    JEL classification:

    • C19 - Mathematical and Quantitative Methods - - Econometric and Statistical Methods and Methodology: General - - - Other
    • I20 - Health, Education, and Welfare - - Education - - - General

    NEP fields

    This paper has been announced in the following NEP Reports:


    Access and download statistics


    All material on this site has been provided by the respective publishers and authors. You can help correct errors and omissions. When requesting a correction, please mention this item's handle: RePEc:col:000089:012061. See general information about how to correct material in RePEc.

    For technical questions regarding this item, or to correct its authors, title, abstract, bibliographic or download information, contact: (Universidad De Los Andes-Cede). General contact details of provider: .

    If you have authored this item and are not yet registered with RePEc, we encourage you to do it here. This allows to link your profile to this item. It also allows you to accept potential citations to this item that we are uncertain about.

    If CitEc recognized a reference but did not link an item in RePEc to it, you can help with this form .

    If you know of missing items citing this one, you can help us creating those links by adding the relevant references in the same way as above, for each refering item. If you are a registered author of this item, you may also want to check the "citations" tab in your RePEc Author Service profile, as there may be some citations waiting for confirmation.

    Please note that corrections may take a couple of weeks to filter through the various RePEc services.

    IDEAS is a RePEc service hosted by the Research Division of the Federal Reserve Bank of St. Louis . RePEc uses bibliographic data supplied by the respective publishers.