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The self reported annual frequencies of colds were assessed for two groups of 37 students each who were either consistent or inconsistent in the use of their hands. These data indicated that the inconsistent hand use group reported significantly more colds than their consistent hand use peers.

In this study, we measured the relationship between the consistency of hand use and three symptoms of insomnia, i.e., delayed sleep onset, frequent awakenings during sleep, and trouble returning to sleep after an awakening. For each of these insomnia-related symptoms, university students who were classified as inconsistent in the use of their hands (n = 30) were significantly more likely to report problems than their consistent hand-use peers (n = 30). These data were discussed both in relation to the literature on handedness classification and sleep problems and the emerging literature on consistency of hand use and health-related problems.

We examined relationships between consistency of hand use and falling in groups of right-handed university undergraduates who were either consistent (n = 45) or inconsistent (n = 32) in the use of their hands. A scoring procedure developed for the Briggs-Nebes Handedness Scale permitted us to classify individuals as consistent or inconsistent in the use of their hands. The inconsistent group was 2.81 times more likely to have experienced frequent falls during the last 12-mo. period and was 1.64 times more likely to rate themselves higher on proneness to falling. These data suggest that inconsistent hand use may be a sign of a developmental inconsistency in motor coordination.

In this study, we examined the relationships between the consistency of hand use, exercise, and sports-related injuries as an indirect test of the hypothesis that the consistency of hand use is a reflection of general motor coordination. As we predicted, the consistent hand-use group (n = 23) exercised more, were more likely to follow a regular exercise schedule, and reported having experienced more sports-related accidents than their inconsistent hand-use peers (n = 23).

The responses of 116 university students were used to assess a possible relation between scores on Hartmann's Boundary Questionnaire and the Briggs-Nebes Handedness Scale. Consistent with our prediction, the mean handedness score of the students with thin boundaries was significantly skewed in the direction of mixed-handedness.

In this study, we examined the relationship between the consistency of hand use and the self-reported incidence of accidents with injuries which required medical care in groups of university students (n = 23 for each group). To do this, we adopted a scoring procedure for the Briggs-Nebes Handedness Scale that permitted us to classify individuals as consistent or inconsistent in the use of their hands. We observed that the inconsistent group was 6.12 times more likely to have experienced accidents with injury that required medical care than the consistent group. These data have implications for the literature on handedness classification and accidents. Collectively, these limited data underscore the need to pay attention to the consistency of hand use in research on handedness, health, and longevity.

Response of groups of 163 right-, 22 mixed-, and 20 left-handed university students to the seven symptom subscales of a 48-item Stress-related Health Problems Scale were used to test the hypothesis that left-handedness is associated with an increased risk of stress-related health problems. Since only one of the 21 possible statistical tests computed barely reached statistical significance, there is no meaningful relationship between handedness and stress-related health problems.

In support of the argument that left-handedness is a marker for decreased survival fitness, in 1991 Coren and Halpern gave considerable weight to the results of their 1988 study in which right-handed baseball players were described as having lived about eight months longer than their left-handed peers. In their 1993 unsuccessful attempt to replicate this study, Fudin and colleagues cited certain difficulties with the sources of these data that led them to recommend a comprehensive third study which included only reliable data from the two current editions of the major sources of information on Major League baseball players, i.e., the 1993 editions of The Baseball Encyclopedia and Total Baseball. Following this suggestion, we measured the life spans of all baseball players, i.e., right-, left-, and mixed-handed players, for whom reliable data were available (N = 5441) and found that the relationship between handedness and longevity was not significant. Unlike Halpern and Coren we noted that right-handed players could be described as having lived about eight months less than their left-handed peers.

As evidence for the hypothesis on the claim of reduced longevity for left-handers, Coren in 1989 reported data which suggested that left-handers were 1.89 times more likely to report injuries which required medical attention. This left-handed group included both left- and mixed-handed individuals. To clarify the results of his study, we repeated in part Coren's study but defined handedness so that groups of right-, mixed-, and left-handed individuals were considered. In contrast to Coren's data, we found that right- and left-handers did not differ significantly in the frequency with which they reported having experienced accidents with injury and that mixed-handers reported being significantly more likely to have had an injury-accident than either right- or left-handers. These data underscore the need to consider mixed-handedness as a separate group in studies of this type.

In an attempt to clarify the relationship between self-reported birth complications and handedness, the handedness distributions of 181 college students who reported birth complications and 1320 students who reported no complications were compared. The results suggest a clear but modest shift in the birth complications group away from the dextral end of the continuum. However these data did not validate the hypothesis that left-handedness results from birth complications.

The hand preference of college students correlated significantly with the writing hand of their biological parents but not that of their stepparents. The results are consistent with a genetic theory of the origin of human handedness.

The anxiety scores of 23 left-handed, 12 mixed-handed and 35 right-handed college students were compared with the result that right-handers were significantly less anxious then both the left and the mixed-handed groups (which did not differ statistically). Since these data appear to be unique, generalizations from them was thought to be premature.

The handedness distribution of a group of 578 gifted elementary school children (I.Q. = 132) was compared to handedness distribution of 391 non-gifted children (I.Q. less than 132), with the result that the gifted group was significantly less right-handed than their non-gifted peers. These data were discussed relative to Bakan's hypothesis that left-handedness results from stressful prenatal and birth conditions. In addition attention was paid to the possibility of a non-linear relationship between intelligence and degree of right-handedness.

In this study, we attempted to maximize the likelihood of replicating Bakan's (1971, 1977a) observations that left-handedness was more probable in college students who were the progeny of "high-risk" births. To do this, the relationships between handedness and a combination of factors known to be associated with birth risk were computed. The observed relationships proved to be trivial and thus the validity of Bakan's hypothesis was questionned.

The scores of 37 right and 30 left-handed subjects on tests of fluid and crystallized intelligence were compared. Consistent with the hypothesis, it was found that the left-handers were inferior to the right-handers on the Gf task. These data are consistent with those from three earlier studies and serve to question the assertion that there are no handedness related differences in ability.

The differences in habitual sleep duration and absolute deviations in habitual sleep duration from the normative mean between 60 left-, 36 mixed- and 125 right-handed college students were tested. It was found that mixed-handers tend to sleep less and as a group show significantly greater deviations in habitual sleep durations than either left- or right-handers. The heuristic value of this relationship for future research was discussed briefly.

Recently Leviton and Kilty reported that the birth dates of left-handed girls in elementary school display a seasonal trend which peaks in November. We report here a failure to replicate this finding for 257 male and 323 female college students. Further, we have considered the likelihood that the original finding was due to sampling error rather than speculating that environmental factors associated with the season of birth are implicated in the etiology of left-handedness, as Leviton and Kilty have stated.

The relationships between a set of birth-risk factors, i.e., sex, parity, and maternal age, and handedness were computed for 600 elementary school children. None of these birth-risk variables (or relevant combinations of them) were significantly related to handedness. These data further question the validity of the hypothesis that left-handedness results from stressful prenatal and birth conditions.

Right-handed college students (N equals 160) received 10 practice trials on inverted-reversed printing with either the left or right hand followed by 10 additional trials with either the same or the other hand. Half the Ss then received 10 interpolated learning trials of inverted-but-nonreversed printing, while the other half of the Ss worked arithmetic problems. Significant retroactive inhibition occurred for Ss printing with the right hand, but not for Ss printing with the left hand.

Bakan has suggested that left-handedness is the result of left hemishperic pyramidal motor dysfunction following perinatal hypoxia. To a degree support for the validity of this hypothesis rests on Bakan's (1971, 1977a) findings that left-handed college students were more likely the progeny of birth orders designated as "high-risk" than right-handed students. Attempts by others to replicate Bakan's data have been unsuccessful. To achieve a more powerful test of this relationship than has been provided by any single study, the data from the five studies which have considered it were pooled and tested. The resulting correlation between birth order and handedness was near zero.

Groups of 15 left-, 15 mixed-, and 39 right-handers were tested with Rotter's Locus of Control Scale. Contrary to prediction, it was found that both left- and right-handers scored significantly higher, i.e., were more externally controlled, than mixed-handers. Primarily these data suggest a complex relationship between handedness and personality and they serve to reinforce the need to include mixed-handers in research on handedness.

Subjects balanced a dowel rod vertically on the left and right index finger singly and while simultaneously repeating phrases. With right-handed subjects who had no left-handed relatives, concurrent verbalization shortened right- but not left-handed balancing. Increased phonetic difficulty of the phrases produced an increased decrement on right-handed balancing, but left-handed balancing was unchanged; it also produced more verbalization errors on trials with the right hand, but not with the left. Concurrent verbalization shortened balancing duration with both hands of left-handers. Right-handers with left-handed relatives produced variable results. Concurrent humming also selectively interfered with right-handed balancing. It was concluded that the results conform to an interpretation based on intrahemispheric interference between incompatible, simultaneously produced sets of responses.

The relationship between personal and familial hand preference and mental retardation was examined. Six unimanual tasks were performed by 232 subjects within four mental retardation severity groups. Family handedness histories were obtained. Right hand preference varied inversely with severity of mental retardation. The handedness of mentally retarded groups at the different functional levels paralleled, but tended much more to the sinistral, than that of the corresponding parent groups. The parent-proband handedness correlations were largely insignificant, especially in lower functioning groups. The findings support both pathological left-handedness theory and an association between brain damage causing mental retardation and familial sinistrality.