The Aggressive Behavior of Individuals with Intellectual Disabilities is Not Affected by a Full Moon: A 17-Year Study 1

Studies With Intellectually Disabled Individuals

Owens and McGowan (2006) reported that the belief in a lunar effect could reinforce negative stereotypes about people with a mental disorder. Derogatory and stigmatizing terms that have been associated with a lunar effect have included lunacy, Transylvania effect, werewolf, and vampire (Kelly, et al., 1996). One group with a long history of discrimination, mistreatment, stigma, and occasional identification with the mentally ill is individuals with intellectual disability (Cos, 2014i Hewitt, 2014). Because of the stigma experienced by these individuals (who were formerly called mentally retarded), it is critical that any research that has reported a lunar effect receive close scrutiny and verification.

Of the several studies that included individuals with intellectual disabilities in residential facilities, only Hicks-Caskey and Potter (1991) reported a significant lunar effect on behavior. They analyzed 11, 200 log entries that were recorded by direct care staff during the 19 mo. prior to the study and reported that 20 adult female residents with “profound” intellectual disabilities displayed significantly more misbehaviors during the full moon day (M = 2.21 per resident, SD = 1.68) than during the balance of the month (M = 1.43 per resident, SD = 1.63; F = 4.29, p = <.01). Misbehaviors were defined as any behaviors that posed harm or potential harm to others or property, or could be “disruptive” to the daily routine of cottage life. Flynn (1991) reported several potential weaknesses of the study; e.g., the small sample of residents, the limited time period, the subjective nature of the documented behaviors, and the possible confounding of results by not taking into account weekends and holidays. Although controlling for these potential confounding effects was recently stressed by Chudler (2007I, it was initially emphasized by Kelly and Rotton (1983) in their criticism of Templer, Veleber, and Brooner (1982) who reported a lunar effect on traffic accidents. Templer, Corgiat, and Brooner (1983) reanalyzed their data and found that traffic patterns on weekends and holidays differed from other times. After they controlled for the day of the week and holidays, evidence of the lunar effect disappeared. Bell and Redelmeier (2001) and Alspach (2010) reported higher hospital mortality rates during weekends and suggested that this was due to staffing patterns being different during weekends than during weekdays.

In response to the criticisms by Flynn (1991), Hicks-Caskey and Potter (1992) reported that the mean number of misbehaviors per resident per day during weekends and holidays (M = 1.5, SD = 1.7) did not differ significantly from that during the balance of the month (M = 1.6, SD = 1.8). However, they neither separated weekend data from holiday data nor reported data for the full moons that occurred during weekends or holidays. Significantly higher rates for these days with full moons would have added support to their report of a lunar-behavior relationship. Because they did not address Flynn's other criticisms, their results warrant further investigation.

In contrast to Hicks-Caskey and Potter (1991), Gorvin and Roberts (1994) found no lunar relationship (r=−.09) when they used the more objective measure of “dates of emergency psychiatric admissions” in their study of 86 adults with intellectual disabilities who were admitted to a psychiatric hospital over a 35-mo. period. The mean number of admissions was 1.0 the day of the full moon, 3.0 per day the three days before, 3.0 per day the three days after, and 3.5 per day the rest of the month.

Vance (1996) also failed to find a lunar relationship in 131 reports of problem behaviors that were displayed by adults with intellectual disabilities. Over a 34-mo. period, “semiskilled persons” reported behaviors that were unsafe to self or others, running away, extreme noncompliance, and very unusual behaviors such as urinating or defecating on self, and eating feces. The mean number of reports during the full moon week was nearly identical to that of the other three weeks of the month (0.97 vs. 0.96 per week, respectively). Because other data were not reported, it cannot be determined whether there were more behavioral incidents on the actual full moon days than other days. Also, behaviors judged to be unsafe, very unusual, or noncompliant can be criticized as being too subjective and prone to unreliable documentation by semiskilled persons. Finally, the reliability of results is questionable, given the very small number of incidents per week.

Because the Hicks-Caskey and Potter (1991) report of a lunar effect on the behavior of individuals with an intellectual disability can have repercussions with respect to treatment and stigma, I attempted to discover whether an expanded investigation would support their results. Rates of misbehavior on many more full moon and non full moon days were compared, and the criticisms of Flynn (1991) were addressed.

Hypothesis. In a large sample of intellectually disabled individuals, over 17 years, objectively defined behavior analyzed by weekday, holiday, and monthly patterns will show no effect of full moon days.

Method

Participants and Procedure

From 1996 through 2013, the Intermediate Care Facility for Individuals with Intellectual Disabilities (ICF/IID) in a southeastern state typically housed about 120 adult men and women with intellectual disabilities. Most were nonverbal and had profound-to-severe intellectual disabilities. Over half received psychiatric medication, and about 90% had Behavior Support Plans (BSPs) written by psychologists and formally approved by a Human Rights Committee (HRC) composed of community citizens. About one-third of the BSPs allowed physical restraint for intense physical aggression that was directed at people and continued to be dangerous to them after less restrictive interventions were attempted; e.g., using verbal and mild physical prompts to redirect the individual away from the source of anger, giving space (backing off), distracting the individual's attention with an item of interest, blocking dangerous blows with arms or pillows, and asking the individual's favorite staff to try to remove the individual from the area. Physical aggression that required restraint tended to be behaviors such as hitting, kicking, head butting, and/or biting that were intense enough to require two or more direct care or professional staff to hold the individual in a standing, sitting, or prone position on a padded mat until dangerous behavior stopped. The staff was formally trained in verbal and nonverbal de-escalation methods, as well as restraint techniques, during a 2-week hiring orientation period. Refresher sessions were required annually.

Each restraint incident, as well as the less restrictive methods attempted unsuccessfully, were described on an official restraint form that was inspected daily by professional team members, administrative staff, and security officers. Such close inspection increased the likelihood that the aggression was actually toward people and intense enough to justify formal restraint. A summary of the month's restraints was presented to the Human Rights Committee in advance of its monthly meeting. The psychologist who was professionally responsible for the individual who was restrained attended the meeting to defend restraint that was questioned. Restraint reports from June 1996 through May 2013 were analyzed. This period started in the month the Human Rights Committee began to receive the reports until the psychologist responsible for them left employment.

The primary data were frequency or restraint and minutes in restraint on full moon and non-full moon days, as well as restraint-free (zero restraints) days over a period of 17 years. In their reply to Flynn (1991), Hicks-Caskey and Potter (1992) reported that there was no difference in the rate of misbehavior during weekends or holidays and the “balance of the month” over 19 months. However, they neither reported data for their five weekends with full moons nor specified which holidays were included in their analysis. The present analyses included restraint frequency for 58 weekends that had full moons, as well as nine state government paid holidays (New Year's Day, President's Day, Easter Holidays, Memorial Day, July 4th, Labor Day, Veteran's Day, Thanksgiving, and Christmas). Weekends included Saturdays and Sundays.

Results

Over the 17 years, there were 12, 220 restraints and 210 full moons. The mean daily frequency of restraint for full moon days (M = 1.99, SD = 1.8) did not differ significantly from that of non-full moon days (M = 1.97, SD = 0.7; t₂₀₈ = 0.14, p <.89, Cohen's d = 0.01), nor did the mean daily minutes of restraint for full moon days (M = 47.1, SD = 48.6) and non-full moon days (M = 45.2, SD = 20.6; t₂₀₈ = −0.87, p <.39, Cohen's d=−0.09). Contrary to a lunar effect, 24.6% of full moon days and 20.6% of non-full moon days were restraint-free. Although these rates did not differ significantly, fewer restraint-free full moon days than non-full moon days would have been expected, if there had been a full moon effect.

Significantly fewer restraint occurred during weekends with a full moon (M = 1.29, SD = 1.18) than during the Monday-Friday periods with a full moon (M = 2.20, SD = 1.89; t₁₆₆ = 4.17, p <.001, Cohen's d = 0.64). No restraints occurred during 32.5% of the weekends with a full moon versus 19.8% of the Monday-Friday periods with a full moon.

There were also significant differences among the nine holidays because of the very low rate of restraint during Thanksgiving and Christmas (χ₈² = 45.88, p <.001, φ = 0.55). Over the 17 years, the combined total number of restraints for these two holidays was only 15, and 71% were restraint-free. The 17-year restraint total for the other seven holidays was 180, with a much smaller 34% being restraint free. Rates ranged from a low total of 16 restraints for the Easter Holidays to a high of 43 for Memorial Day. Only 20% of non-holidays were restraint-free.

Discussion

Consistent with Gorvin and Roberts (1994) and Vance (1996) who also studied individuals with intellectual disabilities, no relationship between the full moon and behavior was found in the present study. This is contrary to Hicks-Caskey and Potter (1991) who reported a lunar effect with a similar population over 19 mo. and is likely related to the present study's improved time frame and behavioral measure. It included a larger residential sample, a greater number of full moons over the 17 years. Formal restraint reflected only aggressive incidents that were directed at people and were intense enough to result in physical restraint after less restrictive methods were tried.

Weekends and Holidays as Confounding Variables

Results of the current study are in agreement with Flynn (1991), who criticized Hicks-Caskey and Potter (1991) for not considering weekends or holidays as potential confounding variables. Their claim that there were no differences among these and other days (Hicks-Caskey & Potter, 1992) was neither substantiated by the behavioral data in the present study nor the routines in the residential facility. The daily routine on weekends and holidays was considerably different than other days. Monday through Friday activities focused on formal habilitation plans that were developed by a team of staff and relatives. Daily activities were scheduled from waking to bedtime and followed a regular pattern that made it easier for the individuals to learn. The weekday routine was structured, demanding, and often stressful for both individuals and staff. A typical routine in the morning included waking by 6:30 a.m. and bathing, eating breakfast by 8:00 a.m., brushing teeth, getting dressed for work day activities, and being transported to work. Return to the dormitory for lunch occurred at 11:00 and was followed by a return to work until 3:00 pm. Formal habilitation plan activities in the dormitory began shortly after the return from work and an afternoon snack. These were followed by the supper routine, scheduled evening activities, and the bedtime routine.

In sharp contrast, the weekend routine was unstructured, undemanding, and less stressful. The individuals were allowed to sleep past 9:00 am and received a late breakfast. Bathing and dressing did not have to occur at a particular time, and there was no work or transport to prepare for. Weekend activities focused on informal interests that were more enjoyable and relaxing for staff and individuals. Participation by an individual was voluntary, and favorite activities included watching movies, singing and dancing, having picnics, swimming in the campus pool, and taking trips to events in town.

Another significant way that weekends and holidays differed from other days had to do with staffing patterns. To help the regularly scheduled staff have time off approved for weekends and holidays, every dormitory had a list of temporary staff willing to provide coverage. This ensured that a mandated staff-to-individual ratio was maintained. Some of these staff persons were unfamiliar with the individuals and their weekend or holiday patterns. Their behavior was much less predictable to the individuals, and vice versa, than that of the regular staff.

The preponderance of evidence, then, disputes the reliability of the Hicks-Caskey and Potter (1991) conclusion of a lunar effect on the behavior of individuals with an intellectual disability. The results of the present study did not support the claim that weekends and holidays do not differ from other days and agreed with Flynn (1991) who stated that weekends and holidays should be considered confounding variables. Because of stigma that is associated with people who have a psychiatric or intellectual disability (Cos, 2014; Hewitt, 2014), it is imperative that studies that report a lunar effect be replicated with results that are strong enough to be of practical value. Rotton and Kelly (1985b) and Gorvin and Roberts (1994) reported that less than 1% of the variance in their studies could explain a relationship between full moon and behavior. In the current study, behavior requiring restraint was not more likely during a full moon.

Psychosocial vs Geophysical Explanations

Hicks-Caskey and Potter (1991) denied that their positive results were influenced by the staff's psychosocial belief in a full moon effect. In their opinion, if that was the case, then fewer women in their sample would have had no documented misbehaviors. However, because they did not report how many of the 20 women displayed no misbehaviors, this should only be viewed as speculation. In the present study, the rate of physical restraint during weekends and holidays with full moons was significantly lower than that of other days with full moons. This supports a psychosocial explanation, which would more easily explain behavioral differences between the full moon Monday-Friday weekdays and the full moon weekends. It would also explain the behavioral differences among the nine holidays. The fewer number of dangerous behaviors in the more relaxing social environment that is likely to be found on weekends and November-December holiday periods would be more consistent with a psychosocial explanation than a geophysical one.

Limitations and Future Research

Although the negative results in the present study are in agreement with those of others who concluded that there is no lunar effect on the behavior of individuals with intellectual disabilities, there are limitations to the current study. The sample mainly included individuals with profound-to-severe intellectual disabilities who not only lived in a highly supervised ICF/IID residential facility but also displayed aggressive behaviors that were so dangerous to others that intense physical restraint was necessary to stop these behaviors. Although studying individuals who were similar intellectually to those of Hicks-Caskey and Potter (1991) allowed a better comparison of results, individuals with profound-to-severe intellectual disabilities are neither representative of people without an intellectual disability nor even of those with milder intellectual disabilities. Durkin and Stein (1997) estimated that less than 5 per 1000 people had a profound-to-severe intellectual disability and that nearly 85% of them had additional neurological or sensory disorders. About 50% had a known genetic cause for the intellectual disability. This exceptional group might respond differently to possible geophysical and psychosocial lunar effect processes than those who have a milder intellectual disability and no obvious neurological impairment. The individuals in the present study also were likely more dangerous than those of Hicks-Caskey and Potter (1991). Their individuals displayed behaviors that were (1) harmful or “potentially” harmful to people and property and (2) “disruptive” to the daily cottage routine. Because these were combined in the data analysis, it is impossible to determine which was really dangerous or just disruptive. Still, behaviors different and less intense than those in the present study might yield different results.

It would be interesting to compare the behavior rates of individuals with profound-to-severe intellectual disabilities to those of individuals with mild intellectual disabilities during full moon days and other days. Because of their very limited understanding of language, the former individuals would likely have no understanding of possible lunar effects. However, many of the latter individuals might have language ability that is not too different from that of many who do not have an intellectual disability (Editorial Board, 1997). Some might even know about a possible full moon effect. Significant behavioral increases only in those with profound-to-severe intellectual disabilities would support a geophysical effect, while significant behavioral increases only in those with mild intellectual disabilities would support a psychosocial explanation.

Another limitation of the present study is the objective quality of the dependent variable. Analyzed were restraint forms that detailed episodes of intense aggression that continued after less intrusive methods than physical restraint were unsuccessful in stopping the aggression. The professional review of each restraint form, as well as the possible interview of staff that did the restraint, increased the likelihood that the aggression really was intense. Judgment was still used by staff in deciding if the aggression was dangerous enough to justify physical restraint. The behavioral definition in the present study was less subjective than definitions in Hicks-Caskey and Potter (1991), which included behaviors that were “disruptive” and posed “potential harm.” Future studies of behaviors that are defined even more objectively would be an improvement. Inter-rater reliability checks would provide even more confidence in the objectivity. Examples of behaviors that might allow less judgment by the observer are biting others, throwing a hard object at a person, defecating in a place other than a toilet, refusing to eat any food at a meal, refusing to get out of bed in the morning within 10 min. of being asked, and masturbating in a place other than in a bedroom or bathroom stall. The number of reports that document injuries that result in medical attention by a nurse or physician might also provide a reliable objective measure.

Another limitation is that the staff in the large southeastern ICF/IID residential facility of the present study might not be representative of staff caring for a similar population who live in large ICF/IID residential facilities in other regions of the U.S. They might also differ from staff and relatives who care for similar individuals who reside in community settings. Because the staff in the present study's ICF/IID residential facility cares for individuals who tend to be more difficult behaviorally than those who typically reside in less restrictive settings, they might be more prone to blaming the full moon when behaviors escalate. Vance (1995) suggested that staff who supervised individuals who displayed dangerous behavior tended to believe in a lunar effect, to maintain a sense of control and reduce anxiety related to behavioral “outbursts” that were often unpredictable.

A study that investigates how a belief in a lunar effect influences the behavior of staff of a large residential ICF/IID or staff of community group homes for individuals with intellectual disabilities has yet to be conducted. For one example, the staff might simply be asked if the full moon seems to have an effect on the behavior of some of the individuals they care for. Or, questions could come from a more complex objective instrument, such as the nine-item Belief in Lunar Effects (BILE) developed by Rotton and Kelly (1985a). Objective dependent variables might include the amount of leave and tardiness on days with and without full moons. Formal injury reports on staff and individuals might also be analyzed. Similar studies might also be conducted with caretakers who are parents or relatives.

Future Research With the Current Restraint Data

Data from this study might be able to further test the Hicks-Caskey and Potter (1991) lunar effect result, as well as the psychosocial versus geophysical explanations. For example, a comparison of behavior rates when full moons are at perigee, when they are at apogee, and when they appear at other days would be interesting. Lunar perigee is when the moon is closest to the earth every monthly lunar cycle, and lunar apogee is when the moon is farthest from the earth. It can be as close to the earth as 225, 744 mi. and as far away as 251, 966 mi. (World Almanac Books, 2007). Although Kelly, et al. (1996), Dowling (2005), and Chudler (2007) have reported that there has been very little scientific support for the belief that the moon's distance from earth might affect behavior, possibly because of gravitational forces, studies have been few. None have included adults who have intellectual disabilities. The Hicks-Caskey and Potter conclusions about a lunar effect and a geophysical process would be supported if the rate of dangerous behavior was significantly higher than other days when the full moon was at perigee, or significantly lower when the full moon was at apogee. If the full moon perigee and apogee rates during the Monday-Friday period were different from weekend rates, it would likely be due to a psychosocial than a geophysical process.

Final Remarks

In spite of largely negative or weak results over the years, the myth that a full moon has a physical effect on behavior has continued. Chudler (2007) suggested that negative lunar effect results do not interest the media. Consequently, the public has been denied access to the abundant research that does not support a lunar effect. Educating staff during the orientation period about the lack of scientific evidence for a full moon effect, as well as the harmful stigma related repercussions, might be helpful.

This study focused on the Hicks-Caskey and Potter (1991) report of a lunar effect on the behavior of individuals with intellectual disabilities. A lunar effect was not found, consistent with other researchers who studied a similar population. Chudler (2007) noted that although the negative results that have been reported in many studies do not prove that there is no lunar effect, reports of positive results should be based on reliable scientific methodology. Because of the stigma that has been experienced by individuals with intellectual disabilities, the conclusion of a full moon effect, with its negative connotations, requires strong experimental support. When the present study addressed several weaknesses of Hicks-Caskey and Potter revealed by Flynn (1991), such experimental support for a lunar effect was lacking. Much further reliable scientific confirmation of a lunar effect on the behavior of this population must occur before there can be confidence in such a finding.