Experimentation in Psychology--Rationale, Concepts and Issues

An experiment is made up of two or more data-collection conditons that are identical in all aspects, but one. It owes its design to an inductive principle and its hypothesis to deductive logic. It is the most suited for corroborating explanatory theries , ascertaining functional relationship, or assessing the substantive effectiveness of a manipulation. Also discussed are (a) the three meanings of 'control,' (b) the issue of ecological validity, (c) the distinction between theory-corroboration and agricultural-model experiments, and (d) the distinction among the hypotheses at four levels of abstraction that are implicit in an experiment

Matching on-the-fly in Sequential Experiments for Higher Power and Efficiency

We propose a dynamic allocation procedure that increases power and efficiency when measuring an average treatment effect in sequential randomized trials. Subjects arrive iteratively and are either randomized or paired via a matching criterion to a previously randomized subject and administered the alternate treatment. We develop estimators for the average treatment effect that combine information from both the matched pairs and unmatched subjects as well as an exact test. Simulations illustrate the method's higher efficiency and power over competing allocation procedures in both controlled scenarios and historical experimental data.Comment: 20 pages, 1 algorithm, 2 figures, 8 table

Experimenting on Contextualism: Between-Subjects vs. Within-Subjects

According to contextualism, vast majority of natural-language expressions are context-sensitive. When testing whether this claim is reflected in Folk intuitions, some interesting methodological questions were raised such as: which experimental design is more appropriate for testing contextualism – the within- or the between-subject design? The main thesis of this paper is that the between-subject design should be preferred. The first experiment aims at assessing the difference between the results obtained for within-subjects measurements (where all participants assess all contexts) and between-subject measurements (where respondents evaluating different contexts are distinct groups). It is shown that the within-subject design provides data that seems to support contextualism. However, I present an alternative, invariantist interpretation of these results, therefore showing that the within-subject design does not allow to empirically distinguish between contextualism and invariantism. The second experiment further elaborates the issue of how perceiving the contrast between contexts can affect subjects’ judgments – I show that certain kinds of contexts may elicit opposite intuitions when contrasted with different contexts

Beyond statistical testing: individual differences and the contentand accuracy of mental representations of space

The article uses data from two experiments on the content and accuracy of mentalrepresentations of space by the blind and visually impaired in order expose some of theshortcomings of typical statistical testing and propose an individual differences approach to theanalysis of data. It begins with a discussion of some of the problems associated with the strictclassification and eventual comparison of individuals between groups. The individual differencesapproach is then presented and the concepts of ability and present competence are explored alongwith the importance of detailed participant description. Examples from the two experiments areused to demonstrate how null hypothesis significance testing can be complemented with effect sizeestimates, box-plots and ranking techniques. Throughout the article we are reminded of the need toadopt mutually supportive techniques to account for the heterogeneity of experience and skillsbetween participants. The article uses data from two experiments on the content and accuracy of mentalrepresentations of space by the blind and visually impaired in order expose some of theshortcomings of typical statistical testing and propose an individual differences approach to theanalysis of data. It begins with a discussion of some of the problems associated with the strictclassification and eventual comparison of individuals between groups. The individual differencesapproach is then presented and the concepts of ability and present competence are explored alongwith the importance of detailed participant description. Examples from the two experiments areused to demonstrate how null hypothesis significance testing can be complemented with effect sizeestimates, box-plots and ranking techniques. Throughout the article we are reminded of the need toadopt mutually supportive techniques to account for the heterogeneity of experience and skillsbetween participants

An Evaluation of Age Effects on Driver Comprehension of Flashing Traffic Signal Indications using Multivariate Multiple Response Analysis of Variance Models

Objective: The objective of this experiment was to identify whether drivers comprehended traffic signals differently when turning left at signalized intersections where traffic signals were in “flashing mode” operation. Method:Multivariate multiple response analysis of variance models were used to analyze the simultaneous effects of displayed color combination, age, and geographical location on signal message interpretation. Data were gathered in a laboratory environment. Results: Left-turn and through-signal color combination had a significant effect on subject comprehension. Comprehension was found to be lowest for displays flashing red only, followed by displays flashing red on the left-turn, and yellow on the through-signal, with best comprehended displays flashing yellow only. No overall significant age effects were identified, with one minor exception. No geographical region effects were identified. Signal section arrangement and the use of an arrow or circular illuminated lens had no significant effect on comprehension. Discussion: Traffic signal displays in “flashing mode” operation were previously identified as the least well-comprehended displays for drivers turning left. The present effort identified that this is mainly due to displays flashing red indications on the through-signal. Comprehension of displays flashing yellow indications on the through-signal is comparable to that of permitted left-turn indications. Impact on the Industry: There is a need to develop alternatives for signal displays flashing red indications on the through-signal because a large percentage of drivers facing such indications mistakenly think they have the right-of-way when, in fact, they do not. However, use of such displays on minor streets intersecting major streets cannot currently be avoided when signals are placed in flashing operation. Practitioners using flashing signal operations need not be concerned about signal message comprehension differences among age groups. They can use any among the analyzed alternative signals that convey a given message without impacting signal message comprehension

Ingestion of Amniotic Fluid Enhances\ud Opiate Analgesia in Rats

Placenta ingestion has recently been shown to enhance opiate-mediated analgesia produced by morphine injection, footshock, or vaginal/cervical stimulation. The enhancement of the effect of endogenous opiates (especially analgesia) may be one of the principal benefits to mammalian mothers of placentophagia at delivery. During labor and delivery, however, mothers also ingest amniotic fluid (AF) which, unlike placenta, becomes available during, or even before expulsion of the infant. The present experiments were undertaken to determine (a) whether AF ingestion, too, enhances analgesia; if so, (b) whether the effect requires ingestion of, or merely exposure to, AF; (c) whether the effect can be produced by AF delivered directly to the stomach by tube; and (d) whether the enhancement, if it exists, can be blocked by administering an opiate antagonist. Nulliparous Long-Evans rats were tested for analgesia using tail-flick latency. We found that (a) rats that ingested AF after receiving a morphine injection showed significantly more analgesia than did rats that ingested a control substance;' (b) AF ingestion, alone, did not produce analgesia; (c) ingestion of AF, rather than just smelling and seeing it, was necessary to produce analgesia enhancement; (d) AF produced enhancement\ud when oropharyngeal factors were eliminated by delivering it through an orogastric tube; and (e) treatment of the rats with naltrexone blocked the enhancement of morphine-induced analgesia that results from AF ingestion