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Biomedical subjects

C W Melzer

Publications and source records attributed to C W Melzer.

8 recordsLinked to original sources
PubMed1987

A reappraisal of the use of the phi-coefficient in multiple choice examinations.

The phi-coefficient of an item in a multiple choice question (MCQ) examination is often used to determine whether that item is suitable for re-use in future examinations. In order to be of value in this regard, the coefficient must be shown to be an objective and consistent index of the discriminating power of an MCQ item. The behaviour of the phi-coefficient (phi) was investigated in two one-from-five MCQ and two true/false examinations. It is shown that the magnitude of the phi-coefficient for the items in any examination is a function not only of the discriminating power of the items, but also of the magnitude of the countermark for incorrect responses, of the proportion of 'don't know' responses in the examination, and of how the 'don't know' responses are handled in the analysis. It is further shown that the reproducibility of the phi, when calculated for any pair of randomly selected portions of a class of students, is very poor. We conclude that the error of estimation of the phi is of the same order of magnitude as the phi's normal operative range.

Anatomy↗
PubMed1984

Tay-Sachs disease and the persistence of lethal autosomal recessive genes in human populations.

Several lethal autosomal recessive genes have stable carrier frequencies of about 1:20-30 in certain communities, while being exceedingly rare in other, biologically equally successful communities sharing the same environment. It is shown that this situation could persist indefinitely, without invoking the concepts of heterozygote advantage or epistasis, if the parents of affected offspring replace such children with additional sibs. We believe that this could be an important biological mechanism which ensures the maintenance of genetic diversity in the face of natural selection.

Attitude↗
PubMed1983

Penalties in multiple-choice and true-false questions.

In multiple-choice and true-false (T-F) questions a student expresses his ignorance by leaving questions unanswered, guessing randomly, answering according to some predetermined formula, or, in T-F tests, by marking all those which are unknown as 'true' or all as 'false'. Each of these no-knowledge strategies should, on average, yield the same score. It is shown that partial knowledge is awarded part-marks in multiple-choice question and T-F tests, since the chance of guessing correctly is greater when students possess some knowledge than when they guess randomly. There is a constant relationship between the score obtained by the informed guesser and the minimum, maximum and random-guessing scores, this relationship being independent of the scoring system. Modifications of the scoring system (i.e. of the magnitude of the penalty for incorrect responses) affect only the reward for unanswered questions: in the absence of a penalty the reward for unanswered questions equals the minimum score--a score which is unattainable by random guessing; with a large penalty the reward for unanswered questions approaches the maximum score obtainable.

Educational Measurement↗
PubMed1981

The incorrect response in multiple-choice examinations.

There are three causes for incorrect responses in multiple-choice question (MCQ) and true-false (T-F) tests: (i) guessing as a result of total ignorance; (ii) guessing as a result of partial knowledge; and (iii) so-called 'anti-knowledge', which we define as the recording of an incorrect response in the firm belief that it is the correct one. Anti-knowledge responses may have many causes: ambiguity about the words or implied meaning of a question, differences of scientific prejudice or opinion, or because of misconceptions. Whatever the cause, however, anti-knowledge always gives rise to a score which is less than the score obtained through random guessing. This is a major failing of the MCQ type of examination, and there is nothing that can be done about the scoring system to alleviate the problem. Essentially the type of question which might give rise to anti-knowledge responses has to be eliminated from the examination, thus ensuring that partial knowledge is always rewarded by a score equal to or greater than (but never less than) the score for random guessing.

Education, Medical↗
PubMed1976

Misconceptions and miscarriages in multiple choice questions.

A modification of the standard format of multiple choice question (MCQ) examinations, recently introduced in certain medical schools in this country, is decribed. The scheme allows for the variation of marks allocated to different in the paper, depending upon the relevance, importance and degree of difficulty of each question. However, the manner in which this new system is being implemented in some cases transgresses some fundamental principles of MCQ examinations. The consequence of this is that the average mark for the class is unintentionally low, with the good students separated from the main body of the class by a disproportionate number of marks. In addition, the examination lends itself to abuse by the enterprising student who is familar with the system of mark allocation.

Education, Medical, Undergraduate↗
PubMed1975

Down's syndrome with additional XYY aneuploidy.

A further case of Down's syndrome with additional XYY aneuploidy is reported. The child has been followed for 5 years. It has not been possible to recognise any phenotypical feature which distinguishes the patient from others with Down's syndrome.

Aneuploidy↗