Standardized or simple effect size: What should be reported?

It is regarded as best practice for psychologists to report effect size when disseminating quantitative research findings. Reporting of effect size in the psychological literature is patchy – though this may be changing – and when reported it is far from clear that appropriate effect size statistics are employed. This paper considers the practice of reporting point estimates of standardized effect size and explores factors such as reliability, range restriction and differences in design that distort standardized effect size unless suitable corrections are employed. For most purposes simple (unstandardized) effect size is more robust and versatile than standardized effect size. Guidelines for deciding what effect size metric to use and how to report it are outlined. Foremost among these are: (i) a preference for simple effect size over standardized effect size, and (ii) the use of confidence intervals to indicate a plausible range of values the effect might take. Deciding on the appropriate effect size statistic to report always requires careful thought and should be influenced by the goals of the researcher, the context of the research and the potential needs of readers.     

More is more: The relationship between vocabulary size and word extension

This study experimentally tested the relationship between children’s lexicon size and their ability to learn new words within the domain of color. We manipulated the size of 25 20-month-olds’ color lexicons by training them with two, four, or six different color words over the course of eight training sessions. We subsequently tested children’s ability to extend new color words to new instances. We found that training with a broader number of color words led to increased extension of new words. The results suggest that children’s learning history predicts their ability to learn new words within domains.     

The functional properties of a time out from an avoidance schedule

Investigations are reported of some of the discriminative (cue) and reinforcing properties of stimuli (TO_av) correlated with the discontinuation of a free-operant avoidance schedule. After several unsuccessful initial attempts to demonstrate the positively reinforcing effect of TO_av, a special technique was developed. The subjects were trained by means of a free-operant avoidance procedure to press a lever and postpone electric shock; by pressing a second lever, they could produce a cue correlated with the TO_av period. The importance of a distinct cue correlated with TO_av was demonstrated in experiments in which this signal was eliminated from the procedure. The reinforcing function of the TO_av period was explored by showing its effectiveness under various schedules of reinforcement.

Other observations were made concerning the course of extinction of both TO_av-producing responses and avoidance behavior.

In further experiments in which TO_av was used as a reinforcer, the TO_av behavior was also brought under separate stimulus control. The development of the various discriminations involved in the resulting performance were described.