This study assessed in utero exposed adolescents' and their mothers' reports on the adolescents' emotional/behavioral problems. The most noteworthy findings were that in contrast to previous studies of in utero exposed children:
The level of problems reported by the adolescents and their mothers was low.
The level of problems reported by the mothers was generally lower than that reported by the adolescents.
The current study, with a CBCL mean Total Problems score of 11.8, is in accordance with previous Nordic studies, which also reported low CBCL mean Total Problems scores in comparison with studies in other countries . A Swedish study that examined 1308 school children aged 6-16 years old with the CBCL found a mean Total Problems score of 14.2 . A Norwegian study of 1170 children aged 4-16  found a CBCL mean Total Problems score of 15.4. For the subgroup aged 12-16, the mean Total Problems score was 13.6 . In the current study rates of self-reported behavior problems (YSR) were generally higher for the adolescents, with a mean Total Problems score of 31.1, but within the normal range and lower than those reported in another Norwegian study .
The mothers' ratings reported low levels of problems and better psychological functioning than the adolescents reported themselves. Many researchers have reported significant discrepancies between youth-reported and parent-reported psychopathology in adolescents . In studies of nonclinical samples, youths report higher severity ratings than their parents . Our findings are consistent with previous studies comparing parent reports and youth self reports of adolescents' emotional and behavioral problems.
Investigations have documented Chernobyl-related psychological problems in prenatally exposed children in the former Soviet Union [2–4, 22]. The causes of these observed psychological problems are uncertain. The radiation release may have a direct, physiological impact on the developing fetal brain, and/or it may affect the fetus in terms of stress on the mother caused by the perceived danger of exposure to Chernobyl radiation. Other stressful consequences of the accident may also continue to affect the child later on. It is difficult to separate the potential impact of these variables.
In the former Soviet Union, the accident had a tremendous impact on the areas surrounding Chernobyl, both in terms of radiation exposure and psychosocial consequences interfering with people's lives. However, some investigations did not document a rise in psychological and behavioral problems in children exposed in utero or as infants in these areas [5, 6]. In one study , evacuees and non-evacuees obtained high scores on the CBCL problem scale but there were few significant differences between groups. Among the significant differences were maternal ratings of somatic complaints. Evacuee mothers rated their children's well-being as significantly worse, especially on somatic symptoms on CBCL . The most important risk factors for these ratings were somatization and Chernobyl-related stress experienced by the mother. Another study revealed no significant differences between groups related to level of radiation exposure, but mothers who were pregnant at the time of the accident rated their children as significantly more hyperactive . Interestingly, in the Taormina study , evacuee mothers were almost three times more likely to report their children as having memory problems.
In the current data mothers rated their children as having fewer problems than the adolescents themselves reported. This pattern is typical in nonclinical groups. This could indicate that the mothers included in the current study were less worried than the mothers in previous investigations of radiation exposed individuals.
People have a strong tendency to worry about their future health once they know they have been exposed to radiation, even when the dose they have received is negligible . The amount of radiation discharged from the accident at Three Mile Island in the United States was less than one-millionth of the release from the Chernobyl accident, but the Three Mile Island accident seriously affected the mental health of the general population . Why does this not seem to apply to prenatally exposed Norwegians and their mothers?
The passage of time may affect the psychological reactions. Five years after the nuclear accident at Three Mile Island, the mental health of women who were living close to the site and were pregnant at the time of the accident was similar to that of women from the same area who became pregnant after the accident. Maternal ratings of the two groups of children when they were five years old were also similar . In a study of in utero exposed children from the former Soviet Union, Korol and Shibata  found the prevalence of neurotic disorders to be significantly higher in the in utero exposed group from 1989-1997, but the difference diminished in effect from 1999-2003. These findings suggest that the psychological effects change over time. Differences in the timing of investigations may be one explanation of inconsistent findings across studies. The low levels of problems reported in the current study may be explained by the two decades that separated the accident and the investigation.
In a survey study  estimating Chernobyl-related anxiety among Norwegians in the first two months following the accident, the anxiety and stress produced by the accident only reached clinical levels for about 1% of the respondents. Studies that have investigated the effects of toxicological disasters provide evidence of a significant increase in the number of legal abortions , but there was no rise in legal abortions in Norway in the year following the Chernobyl accident . These findings suggest that even though the accident and its consequences in Norway were well known, Norwegians were less worried about the potential impact of exposure to Chernobyl fallout.
Johnson and Galea  have described risk factors associated with mental health problems after disasters. Among these are: direct exposure to the disaster; the degree of exposure to and direct threat from the disaster; participation in rescue and cleanup; media exposure; indirect consequences of the disaster (such as relocation or residential problems and community destruction); proximity to the disaster; being in the disaster-affected area at the time of the disaster; alcohol-related problems since the disaster; events since the disaster; negative life events; demographics; low-medium socioeconomic status or education level; social factors; limited post-disaster help; perceived similarity to victims; and perceived risk.
The risk factors mentioned above were higher for the exposed population from the former Soviet Union than for the Norwegian population living in exposed areas, with the most obvious difference being proximity to the disaster. The exposed population in the former Soviet Union experienced a lack of information, disorderly evacuation, conflicts over housing and benefits, and inadequate medical care . Because of the collapse of the former Soviet Union, there were dramatic changes in the socioeconomic environment as well . This can explain the fact that even though researchers did not document differences between evacuees and controls in Kiev, CBCL problem scores were generally high for both groups [5, 7].
The Norwegian authorities provided systematic measures of ionizing radiation, adequate information about the potential dangers, restrictions on certain kinds of polluted foods, readily available health care and economic compensation for farmers in affected areas. There was no evacuation as a result of the accident. As in the rest of Norway, the participants in this study came from families that enjoyed a high living standard and social security. Higher social class, usually measured by education and income, is associated with better mental health outcomes after accidents . It is likely that these factors have served as a protective buffer against the potentially harmful psychological effects of the accident on Norwegians. The perception of physical and psychological distance from the accident has probably had a protective effect as well.
There are limitations to the present study that need to be emphasized. First, the fact that there were no available accurate measures of radiation exposure to each individual. Second, this study investigated a small population within a limited age range, which meant that the sample size was small. It would have been useful to have a sample that represented all in utero exposed adolescents in the population and a suitable comparison group. Unfortunately, there is a lack of Norwegian data regarding the age group we are studying, and no national norms. On the basis of previous studies, one would expect to find low Norwegian problem scores.
Third, the number of nonresponders in the present study is high. Studies have shown that bias is likely to be introduced through nonresponse by the exclusion of participants who report higher levels of problems . When we look at the demographic characteristics of the nonresponders, including a screening of psychological disorders (MINI SCID), no significant differences were found on these measures. Even though we may assume that the nonresponders would report slightly more problems, it is unlikely that they would be significantly different regarding emotional and behavioral problems. However, the lack of data in the current study makes generalization difficult.
Cultural differences in the levels of problems and in response style can make cross-cultural comparisons between studies difficult. A finding across cultures is higher problem scores in children from lower socioeconomic status (SES), particularly on Externalizing scores . There are significant differences in SES between citizens from Norway and the former Soviet Union. Furthermore, the finding that adolescents usually report more problems than parents  seems to be particularly pronounced in Norway and Sweden, with very low scores on the CBCL and higher scores on the YSR .
Differences in SES and culture could potentially explain the discrepancy between the findings of the current and previous investigations in the former Soviet Union. However, because problem scores in previous studies were more highly rated by mothers in the prenatally exposed groups than mothers in the control groups, we do not think SES and cultural differences in response style fully explain the observed differences between the current and previous Chernobyl studies.
A major strength of this study was the access to demographic characteristics of the nonresponders, including a screening of psychological disorders (MINI SCID). In addition, participants included in this study were drawn from areas that enjoyed a high standard of living. In contrast to other studies, poverty did not affect the results.