Randomization tests: application to single-cell and other single-unit neuroscience experiments.

The application of randomization tests for statistical determination of the significance of experimental manipulations on single cells and other types of single units in neuroscience is described. Applications of standard parametric tests like analysis of variance (ANOVA) and t tests to data from single-subject experiments have been severely criticized for lack of validity and those criticisms are relevant to parametric statistical tests for data from other types of single-unit experiments. A broad class of statistical tests known as randomization tests, on the other hand, has been free of such criticism. Randomization tests have been applied to data from various types of single units in neuroscience, where their validity in the absence of random sampling makes them especially valuable. Until the advent of computers, the computational requirements of randomization tests rendered them impractical. Randomization test computer programs are now readily available. Procedures for access to a public domain program are given in the text.

Randomized single-subject experimental designs.

Books on single-subject methodology tend to focus on traditional operant research techniques and thus provide little or no discussion of random introduction of treatments and statistical tests based on such randomization, i.e. randomization tests. Those books are the principal references to which researchers must turn for a comprehensive coverage of single-subject methodology, and so many researchers are likely to be unaware of the relevance of randomization (random assignment of treatment times to treatments) and randomization tests to single-subject experimentation. That is unfortunate because randomization is necessary in order to draw valid statistical inferences about treatment effects. The role of randomization in providing control over major threats to internal validity is explained in this article, and a number of randomized single-subject designs and their applications are provided. Appropriate rank tests are specified, and sources of free software for other, more complex, statistical tests are given.

Randomization tests for restricted alternating treatments designs.

Alternating Treatments Designs (ATD) with random assignment of the treatments to the measurement times provide very powerful single-case experiments. However, complete randomization might cause too many consecutive administrations of the same treatment to occur in the design. In order to exclude these possibilities, an ATD with restricted randomization can be used. In this article we provide a general rationale for the random assignment procedure in such a Restricted Alternating Treatments Design (RATD), and derive the corresponding randomization test. A software package for randomization tests in RATD, ATD and other single-case experimental designs [Van Damme & Onghena Single-case randomization tests, version 1.1, Department of Psychology, Katholieke Universiteit Leuven, Belgium] is discussed.

The failure of antimotion sickness medication to improve reading in developmental dyslexia: results of a randomized trial.

Although there have been no randomized clinical trials of the efficacy of antimotion sickness medication treatment of developmental dyslexia, some children are treated in this way. We have performed two evaluations of such treatments. In Experiment 1, 12 children participated in a double-blind within-subject crossover design to test the acute (2-day) administration of four preparations: 10 mg methylphenidate, 12.5 mg meclizine, both methylphenidate and meclizine, or placebo. Improvements obtained with each drug were scattered across measures of reading fluency, balance and coordination, and eye movements, suggesting that a chronic trial would be justified. In Experiment 2, six children from Experiment 1 received 12.5 mg meclizine b.i.d. for 3 months and placebo for 3 months in a double-blind within-subject crossover design. Meclizine had no effect on reading, but it significantly improved ocular motor stability during steady fixation. This study thus failed to support the hypothesis that meclizine is of benefit in developmental dyslexia.

Scoring rod-and-frame tests: quantitative and qualitative considerations.

An examination of current scoring procedures on the rod-and-frame test showed that these procedures depend on unrealistic assumptions about subjects' performance on the rod-and-frame test. A more general scoring procedure with more realistic assumptions was outlined and illustrated. Like the 1974 Nyborg procedure, this one (a) corrects for constant error, an error unrelated to current concepts of field dependence, (b) is sensitive to a subject's response strategy and choice of cues, i.e., a subject's qualitative aspects of rod-and-frame test performance, and (c) discriminates consistent from inconsistent responding. However, unlike Nyborg's procedure, this one also expresses field dependence relative to maximal field dependence given a subject's response strategy and choice of cue and utilizes all available information. This procedure is useful for the investigation of qualitative and quantitative aspects of rod-and-frame test performance and individual differences in laterality bias as defined by a constant error. Since this scoring procedure relies on computer scoring, a FORTRAN program has been made available.