External Control Group Research Articles

Menstrual function in workers exposed to toluene.

Rates of menstrual disorders were studied in 231 female production workers with high exposure to toluene (mean 88 (range 50-150 ppm) in a factory manufacturing audio speakers and compared with a control group of 58 female production workers in other departments in the same factory who had little or no exposure to toluene (0-25 ppm). An external community control group of 187 working class women under routine care at public maternal and child health centres were also studied. Detailed menstrual and reproductive histories were obtained by personal interview using a structured questionnaire. The rates for dysfunctional uterine bleeding (cycle irregularity and prolonged or heavy menstrual bleeding) were similar in all groups. Dysmenorrhoea seemed to occur more often in the women highly exposed to toluene compared with women at maternal and child health centres, but not compared with factory controls with low exposure to toluene. There was no evidence that dysfunctional uterine bleeding was likely to result from exposure to toluene. It is uncertain whether dysmenorrhoea was associated specifically with exposure to toluene, as other behavioural and work related factors may also result in dysmenorrhoea.

Distribution of 3H‐proline within transseptal fibers of the rat following release of orthodontic forces

Maxillary right first molar teeth of rats were tipped mesially with an orthodontic appliance for 2 weeks (experimental group), 3H-proline was injected, and orthodontic forces were removed 6 hr later (time 0). The contralateral molar teeth of treated (internal control group) and age- and weight-matched untreated animals (external control group) were also studied. Diastemata were created between the molar teeth by the orthodontic appliance, and transseptal fibers between first and second (P less than 0.001) and second and third molars (P less than 0.005) were significantly lengthened as compared to external and internal controls at time 0. Diastemata between molar teeth were closed 5 days after removal of orthodontic force. Transseptal fibers adjacent to the source of the orthodontic force (mesial region) had the highest mean number of 3H-proline-labeled proteins at time 0 and at all times following removal of the force (P less than 0.001), and had the highest rate of labeled protein removal (P less than 0.001). Half-lives for removal of 3H-proline-labeled transseptal fiber proteins were significantly greater in mesial and distal regions and significantly less in middle regions of experimentals than in corresponding regions of external controls (P less than 0.001). These data suggest the following: 1) transseptal fibers adjust their length by rapid remodeling in regions experiencing a tensile force; 2) collagenous protein turnover within the middle third of the transseptal fibers is more rapid subsequent to release of orthodontic force than during normal physiologic drift, suggesting that this region adapts rapidly to changes in adjacent tooth position and that these fibers do not play a significant role in relapse of orthodontically relocated teeth; and 3) significant differences in turnover rates of 3H-proline-labeled transseptal ligament proteins of external and internal control quadrants suggest that tooth movement produces both local and systemic effects on collagenous protein metabolism.

Activation of tri-substituted nitrosoureas by amidases. An SCE study in V79-E cells

Severe airways obstruction and bronchiolitis obliterans have been reported in microwave popcorn production workers and attributed to inhalation of flavoring agents. We investigated whether exposure to flavoring agents is associated with airways inflammation in popcorn production workersFifty-nine workers with high exposures and 22 patients with low exposures to flavoring vapors completed a questionnaire, spirometry, and sputum induction. Sputum cell counts were categorized as “high” if greater than (and “low” if less than or equal to) the median cell counts of a healthy external control group (n = 24). We compared high-and low-exposure groups as well as all workers with control subjectsNeutrophil concentrations in nonsmoking workers were significantly higher than those of the healthy nonsmoking control group (p < 0.05). The smoking-adjusted odds ratio for high neutrophil count (> 1.63 × 105/mL) was 3.8 (95% confidence interval, 1.3 to 11.5) in the high-exposure group compared with the low-exposure group. Sputum interleukin-8 and eosinophil cationic protein levels were higher in high-exposure workers than in low-exposure workers (p < 0.05). For the worker group, mean values of FEV1percentage of predicted and FEV1/FVC percentage of predicted were > 95%. There were no relationships between sputum characteristics and the presence of airways obstructionHigh exposure to popcorn flavoring agents is associated with neutrophilic airway inflammation in popcorn production workers. These data provide further evidence that popcorn production workers face a significant occupational hazard through exposure to flavoring agents

A prospective study on the lack of development of antisperm antibodies in women undergoing intrauterine insemination

To test the hypothesis that intrauterine insemination with washed spermatozoa induces antisperm antibody formation, we measured serum antisperm antibody levels by the Immunobead technique in a population of women receiving exogenous gonadotropins. Antibody levels were measured before therapy (baseline) and then serially during subsequent stimulation cycles, for a maximum of six cycles. Twenty-eight patients underwent intrauterine insemination; each patient served as her own control. An additional 25 patients were treated with exogenous gonadotropins but did not undergo intrauterine insemination; they served as external controls. Antisperm antibody levels in women who underwent concomitant intrauterine insemination were compared with levels in those who did not. Of the 53 enrolled patients, 18 completed six treatment cycles, and 35 achieved pregnancy before six cycles. Forty-five patients (85%) had less than 10% Immunobead binding, six (11%) had binding between 10% and 25% (mean 16%, range 14% to 20%), and two had binding greater than 25% (28% and 42%, respectively). Mean binding was similar (less than 10%) in the intrauterine insemination and external control groups. Eighteen patients conceived in the intrauterine insemination group and seventeen in the control group. Of patients who conceived, all but one had less than 10% Immunobead binding at the time of conception (mean 1.6 months). In patients who did not conceive, there was no difference in Immunobead binding between control and intrauterine insemination groups after 6 months of therapy. Our data do not support the hypothesis that serum antisperm antibody levels, as detected by Immunobead binding, will increase in menotropin-stimulated women undergoing intrauterine insemination over a prolonged treatment period.

Chronic exposure of primates to 60-Hz electric and magnetic fields: III. Neurophysiologic effects.

The neurophysiologic effects of combined 60-Hz electric (E) and magnetic (B) fields, of magnitudes comparable to those produced by high-voltage powerlines, were investigated in 10 monkeys (Macaca nemestrina). Six animals (experimental group) were each exposed to three different levels of E and B fields: 3 kV/m and 0.1 G, 10 kV/m and 0.3 G, and 30 kV/m and 0.9 G. Field exposures were preceded and followed by sham exposures, during which factors of field generation were present (e.g., heat, vibration, noise, etc.) without E and B fields. Each of the five segments (i.e., the three exposure segments and the initial and final sham exposure segments) lasted 3 weeks. Animals were exposed for 18 h/day (fields on at 1600 h, off at 1000 h). Four other animals (external control group) were given sham exposure for the entire 15-week period. Auditory, visual, and somatosensory evoked potentials were recorded twice a week, during the daily 6-h field-off period. E- and B-field exposure had no effect on the early or mid-latency evoked potential components, suggesting that exposure at these levels has no effect on peripheral or central sensory afferent pathways. However, there was a statistically significant decrease in the amplitudes of late components of the somatosensory evoked potential during the 10kV/m and 0.3 G, and 30 kV/m and 0.9 G exposure levels. This result is possibly related to the opiate antagonist effect of electromagnetic field exposure reported by others.

Choice of control population in studies of adverse reproductive effects of occupational exposures and its effect on risk estimates.

Cohort studies of adverse reproductive effects of occupational exposures that compare the outcome of exposed pregnancies with non-exposed pregnancies among the same group of mothers (internal controls) and among a different group of mothers (external controls) have been reviewed. Confounding of the hypothesised associations by parental characteristics, the outcome of previous pregnancies, and other exposures is not adequately assessed in these studies. The risk of an adverse outcome appears to be consistently higher among the external control group of pregnancies than among the internal controls. If the differences between the two control groups are real, comparisons based on external controls underestimate the relative or attributable risk. Alternative explanation for this phenomenon are discussed. A likely explanation is a misclassification of exposure or a high prevalence of risk factors other than the exposure of interest among the external controls. Non-exposed pregnancies among exposed mothers may be used for comparison in preference to pregnancies among non-exposed mothers.

An epidemiological study on the effect of N, N'-methylene-bis-(2-amino-1,3,4-thiadiazole) (MATDA) on outcomes of pregnancy.

A retrospective cohort study on the effect of the suspected teratogenic pesticide N, N'-methylene-bis-(2-amino-1,3,4-thiadiazole) (MATDA) on outcomes of pregnancy was conducted. The exposed group (6,173 pregnancies) was composed of childbearing women who, during their gestation, consumed rice harvested from a field where MATDA had been applied. The control I group (10,145) came from an adjacent county where MATDA had never been used; the control II group (3,326) consisted of women who had been pregnant previous to the introduction of this pesticide in the same region as the exposed group. The validity of the survey was verified by comparability and data-checking studies. After adjustment for the calendar year, maternal age, and pregnancy order, no significant differences were found in rates of spontaneous abortion, fetal death and stillbirth, birth defects, as well as in sex ratio and birth weight between the study groups. The same result was found in the comparison of individual categories of malformation. The rates of the birth defects were 23.84, 21.49, and 22.78 per 1,000 live births for the exposed, internal, and external control groups, respectively. No dose-response relationship was revealed. The results were consistent with previous reports and indicated the difference between animal experiments and human exposures. Although MATDA is teratogenic in animals, it is clear that the pesticide does not adversely effect outcomes of pregnancy in humans as currently applied.

Length and circumference measurements in one-joint and multijoint muscles in rabbits after immobilization.

In this article, we compared changes in the length and circumference of the soleus and the plantaris muscles in rabbits. The rabbits were assigned to a nonimmobilized external control group (n = 4), an experimental shortened-position group (n = 10), or an experimental lengthened-position group (n = 9). One hind limb of each animal in the experimental groups was immobilized in a cast for four weeks to put the muscles in either a shortened or lengthened position. The contralateral limb served as an internal control for the animals in the experimental groups. After the immobilization period, the limbs were fixed in situ, the muscles were dissected, and length and circumference measurements were taken. In both experimental conditions, the immobilized soleus muscles were shorter than their contralateral counterparts (p less than .05); the length of the plantaris muscles did not change. The immobilized muscles had decreased circumference values regardless of the immobilization angle. When compared with the control condition, the shortened soleus muscles had a greater decrease in circumference than did the plantaris muscles. More connective tissue was observed in the muscle bellies of the soleus after immobilization than in the plantaris. Similar significant changes (p less than .05) were found in the nonimmobilized limbs of the animals in the experimental groups. Specifically, the soleus muscles demonstrated length and circumference changes, whereas the plantaris muscles showed changes only in circumference. These findings suggest that when a weight-bearing limb is immobilized, adaptations in gross muscle length and circumference are to be expected in the involved and uninvolved limbs. An assessment of similar adaptations in humans should be a part of the evaluation during recovery.

Prevalence of chest symptoms in nonexposed blue-collar workers.

Epidemiological investigations of lung disease induced by occupational exposures often require prevalence estimates for various respiratory symptoms in subjects without the exposure in question. A standard respiratory questionnaire was administered to carefully selected, nonexposed blue-collar workers (n = 1,372), and linear logistic prediction equations were developed for nine symptoms. For each smoking status, equations were fit employing race, sex, age, height, weight, and education as independent variables. These results can be used as descriptive statistics, as prediction equations from an external control group, and as a guide for selecting risk factors for adjustment of symptom prevalences in other population studies.

Some Effects of a Job Enrichment Program: A Field Experiment.

This field experiment utilized internal and external control groups to assess effects of a job enrichment program. The results generally supported the Job Diagnostic Model concerning core job dimensions and satisfaction measures but also provided indications of a negative Hawthorne Effect and that positive effects on productivity are short-lived. Job enrichment programs are currently or have been or will be employed by literally scores of organizations and millions of dollars expanded annually for such programs (Hamner & Organ, 1978)--all on the premise that job redesign or enrichment programs will enhance employee job attitudes and performance (cf., Hackman & Oldham, 1976). One prominent approach to understanding job enrichment is the job characteristics model developed by Hackman and his colleagues (c.f., Hackman & Lawler, 1971; Pierce & Dunham, 1978; Hackman & Oldham, 1975). Their approach has led to the identification of five core job dimensions--skill variety, task identity, task significance, autonomy, and feedback from the job--which they consider necessary for enrichment. Their data suggest that people who work in jobs that incorporate the five core job dimensions will experience job enrichment and, as a consequence, express greater satisfaction and also produce more and higher quality work. And, there is considerable evidence, provided by others (e.g., Cummings, Molloy, & Glen, 1977; Pierce & Dunham, 1976) which support Hackman and his colleagues' findings, but largely with respect to the predictions about increased satisfaction. Relationships between job enrichment and performance, on the other hand, have been found to be somewhat less encouraging (Pierce & Dunham, 1976 & 1978).

Occupational exposure to hexachlorocyclohexane. II. Health conditions of chronically exposed workers.

Sixty male workers in a lindane (gamma-hexachlorocyclohexane)-producing factory were examined with regard to health in comparison with an external control group of 20 clerks. Case history, physical examination, neurologic status, and ECG revealed no significant differences between groups. However, the following significant differences in clinical-chemical blood tests were ascertained: higher polymorphonuclear leukocyte count, lower lymphocyte count, higher reticulocyte count, lower prothrombin (Quick's) test, and lower blood concentrations of creatinine and uric acid. No significant differences were observed in total red and white blood cell as well as platelet counts, hemoglobin content, the other counts of differential blood picture, gamma-GT, GOT, GPT, LDH, cholinesterase, triglycerides, cholesterol, and urea. In spite of a pronounced exposure to the alpha-, beta-, and gamma-isomers of hexachlorocyclohexane, no signs of severe impairment of health were observed; only small deviations in some laboratory tests were found having no pathologic significance. However, biological monitoring and health supervision of HCH-exposed workers should be carried out.

Social facilitation

Video-recording procedures have been used in previous research as a motivational manipulation. The present study investigated the permanent recording o f behavior as a manipulation o f evaluation apprehension and its effects upon behavioral performance and upon autonomic arousal. Twenty-four subjects (12 males, 12 females) were randomly assigned to one o f four conditions formed by completely crossing two levels o f audience status (peer or authority) with two levels o f behavioral record (nonpermanent or permanent). Another 24 subjects were assigned to an external control group to the 2 X 2 design. Subjects'performance on a hidden-word task and their arousal level (as assessed by the Palmar Sweat Index) were measured. Analyses o f variance results showed a significant performance (p<.05) and a significant arousal (p<.05) difference between the behavioral record conditions as predicted. The control group was also found to be significantly (p < .05) different f rom the experimental groups on the behavioral performance measure. The results were related to previous research findings and interpreted within the context o f the evaluation apprehension notion presented within social facilitation research.

Cognitive and affective response as a function of relative hemispheric involement.

We sought to determine the cognitive and affective reaction to a communicative stimulus as a function of relative hemispheric involvement, and to examine by inference the internal composition of these processes. Right-handed men were asked to evaluate the sound quality of a taped radio broadcast. Each subject (n = 10) subsequently heard either a personally relevant or irrelevant advocacy that was either proattitudinal or counter-attitudinal. An additional ten right-handed men heard a neutral and obscure news story and constituted an external control group. After listening to the tape, subjects rated their agreement with the advocacy and listed their thoughts. EEG activity was recorded from the left (P3) and right (P4) parietal lobes, was integrated through an 8–13 Hz band-pass filter, and transformed to yield a ratio score of the differences between alpha activity in the right and left hemispheres over the sum of the alpha activity in the right and left hemispheres (P4 − P3)/(P4 + P3). Subjects then were ...

A comparison of the effects of external control and self-control on the modification and maintenance of weight.

In an experimental study of weight reduction, 62 obese men and women were administered a pretreatment questionnaire and randomly assigned to three experimental treatment groups: (a) an external control group with a nonrefundable contingency; (6) a self-control group with a refundable contingency; and (c) a self-control group with a nonrefundable contingency. The results indicated that the self-control and external-control treatments were equally effective in producing reduction in weight. However, both self-control interventions were more effective than the external-control intervention in promoting maintenance of weight loss.

NEUROLOGICAL STUDIES IN FAMILIES WITH LEBER'S OPTIC ATROPHY

In this study 289 individuals from 5 pedigrees with Leber's optic atrophy (L. O. A.) were examined neurologically and the symptoms observed were expressed by numerical values, according to an arbitrary number scale; 34 of the 289 were patients suffering from the optic atrophy. Of these 34 patients with L. O. A., 24 were found to have minor neurological abnormalities, a finding which was corroborated by an analysis of previously published reports. A gradual decline in the percentage of individuals with abnormalities was observed in different groups in the following order: Leber patients–brothers of Leber patients–sisters of Leber patients–group of individuals connected through females to the pedigrees (“female line” group)–external control group–group of individuals connected through males to the pedigrees (“male line” group or internal control group). Three of the pedigrees were included in the study because in each of them a patient with a severe neurological disorder was present, diagnosed as spastic paraplegia (1) and multiple sclerosis (2). Evidence is presented that the association, mostly in females, of Leber's optic atrophy and a multiple sclerosis-like neurological disorder cannot be coincidental. Leber's optic atrophy seems to be an affection of the central nervous system not necessarily restricted to the optic nerves.

Internal versus external control and ethnic group membership: a cross-cultural comparison.

Internal versus external control and ethnic group membership: a cross-cultural comparison.