Sample

The Nigerian Survey of Mental Health and Well-Being (NSMHW), fielded between February 2002 and May 2003, was designed to study the prevalence, impact and antecedents of mental health disorders in a representative sample of adult Nigerians, aged 18 years and over. The study was conducted in 21 out of Nigeria's 36 states (collectively representing 57% of the national population). Interviews were carried out in Yoruba, Hausa, Igbo and Efik languages.

A full description of the methods, including quality control measures, have been provided in earlier publications ^{Reference Gureje, Lasebikan, Kola and Makanjuola17,Reference Gureje and Lasebikan18} and only a brief summary is presented here. Four-stage probability sampling was employed with the final stage being the selection of one person per household for interview. The selected individual had to be 18 years or over and fluent in one of the languages of the study.

The overall response rate was 79.3%. The survey was administered in two parts. The part I interview was administered to all respondents (sample size 6752) and consisted of core diagnoses. Part II was administered to respondents who met lifetime criteria for disorders from the part I interview and a probability subsample of other respondents. Part II consisted of assessment of risk factors, consequences and correlates of disorders. The total part II sample was 2143. This report is based on data from this part II subsample; which was composed of about 51% women with more than 50% aged less than 35 years. Table 1 presents the age and gender distribution. Ethical approval was obtained from the University of Ibadan/University College Hospital, Ibadan, joint ethical review board.

Table 1

Demographic distribution of the part II sample of the Nigerian Survey of Mental Health and Well-Being

	Unweighted, %	Weighted, %	Census, %
Age, years
18-24	27.8	27.0	27.0
25-29	15.6	15.2	15.2
30-34	10.2	13.1	13.1
35-39	8.9	10.4	10.4
40-44	8.5	8.0	8.0
45-49	6.7	6.0	6.0
50-54	4.8	5.8	5.8
55-59	3.0	4.8	4.8
60-64	5.2	3.7	3.7
65-69	2.6	2.7	2.7
70-74	3.0	1.8	1.8
≥ 75	3.7	1.7	1.7
Gender
Male	56.2	49.0	49.0
Female	43.8	51.0	51.0

Measures

Statistical analysis

To take account of the stratified multistage sampling procedure and the associated clustering, weights were derived and applied to the rates presented in this report. The weights were adjusted for the differential probabilities of selection and to match the sample to the total Nigerian population with regard to sociodemographic and geographical data. They also adjusted for the oversampling of part I respondents with core disorders.

The associations between childhood adversities and lifetime DSM–IV disorders were estimated in discrete-time survival models with person-year as the unit of analysis pooled across different DSM–IV disorders controlling for age-at-interview and gender. Six separate bivariate models were estimated, one for each adversity. The multivariate additive model included a separate dummy variable predictor for each of the six adversity groups in a single prediction equation. Odds ratios (OR) and 95% confidence intervals (CI) are presented. The level of significance was set at 0.05, two-tailed.

Prevalence of childhood adversities

The estimates of adverse childhood experiences are shown in Table 2. Over 40% of the 2143 respondents had experienced an adversity and 31.2% had experienced two or more adversities. The prevalence ranged from 1.2% for family violence and parental criminal behaviour to 20.9% for the category of parental divorce or other parental loss. Among individuals who reported any single category of adversity, the probability of being exposed to any additional category ranged from 43.5 to 63.2%. The chances of multiple adverse childhood experiences were higher among individuals reporting neglect or abuse and those whose parents had a mental health or substance use disorder.

Table 2

Prevalence of adverse childhood experiences

Category	Weighted n	Prevalence of adversity % (s.e.)	Experiencing 2 or more adversities % (s.e.)	Number of adversities among those with 2 or more adversities, mean (s.e.)
Death of parent	410	19.1 (1.1)	45.0 (3.6)	2.2 (0.0)
Other parental loss	448	20.9 (1.0)	43.5 (2.8)	2.3 (0.1)
Parent mental health or substance use disorder	73	3.4 (0.4)	61.7 (7.3)	2.5 (0.1)
Family violence/criminal behaviour	27	1.2 (0.3)	53.8 (12.6)	2.5 (0.2)
Neglect or abuse	256	11.9 (0.7)	63.2 (4.8)	2.3 (0.1)
Other adversity	150	7.0 (0.9)	54.1 (5.4)	2.3 (0.1)
Any adversity	990	46.2 (1.1)	31.2 (2.2)	2.2 (0.0)

Associations between childhood adversities and mental health disorders

Table 3 shows the estimated effects of adverse childhood experiences on the lifetime risk of DSM–IV disorders. In the bivariate model there was an 11-fold increased risk for meeting the diagnostic criteria for a lifetime DSM–IV disorder in those whose parents had a mental health or substance use disorder; this risk remained substantial even in multivariate additive model analyses (OR = 9.81, 95% CI 2.14–45.09). This increased risk was however no longer significant in the multivariate interactive survival model where the number of childhood adversities experienced by the respondent was taken into consideration.

Table 3

Estimated effects of adverse childhood experiences on lifetime risk of DSM–IV disorders in bivariate, multivariate additive and interactive survival models

Effect	Bivariate modela OR (95% CI)	Multivariate additive model,a OR (95% CI)	Interactive survival modelb OR (95% CI)
Death of parent	2.0 (0.4-9.7)	1.8 (0.4-8.6)	2.4 (0.4-13.1)
Other parental loss	0.7 (0.2-2.7)	0.5 (0.1-2.3)	1.0 (0.2-6.40)
Parental mental health or substance use disorder	10.9 (1.9-63.0)*	9.8 (2.1-45.1)*	5.4 (0.8-35.5)
Family violence	0.7 (0.3-1.7)	0.6 (0.2-1.8)	0.4 (0.1-1.7)
Neglect/abuse	3.0 (0.8-11.7)	2.5 (0.8-7.4)	1.5 (0.5-5.0)
Other adversity	0.3 (0.1-0.6)	0.3 (0.1-0.6)	0.5 (0.2-1.4)

Table 4 shows the estimated effects of the number and types of adverse childhood experiences on the lifetime risk for developing mood, anxiety and substance use disorders. Even though anxiety disorders were not significantly related to any of the specific categories of adverse childhood experiences, there was nevertheless a 12-fold risk of developing them among individuals who had experienced three or more childhood family adversities compared with those with no such experience. The risk for having substance use disorders was increased in those who grew up in families where they were exposed to violence and those who were neglected or abused, whereas parental psychopathology was associated with a significantly increased risk for developing mood disorders. Loss events did not predict the occurrence of any of the DSM–IV disorders examined in this study.

Table 4

Estimated effects of types and numbers of adverse childhood experiences (ACE) on the lifetime risk of three classes of DSM–IV disorders^a

	Mood disorders OR (95% CI)	Anxiety disorders OR (95% CI)	Substance use disorders OR (95% CI)
Parent death	2.2 (0.5-10.5)	0.5 (0.3-1.2)	0.9 (0.4-1.9)
Other parent loss	0.9 (0.2-4.9)	1.1 (0.3-3.6)	1.0 (0.5-1.9)
Parent mental or substance use disorder	6.3 (1.2-32.9)*	1.7 (0.6-4.9)	1.8 (0.4-7.7)
Family violence/criminal behaviour	0.7 (0.1-3.5)	0.7 (0.2-2.0)	5.6 (2.5-12.9)*
Neglect/abuse	1.4 (0.4-4.6)	1.6 (0.9-3.1)	3.4 (2.2-5.4)*
Other adversity	0.4 (0.1-1.2)	1.1 (0.4-2.8)	1.2 (0.6-2.5)
Experience 2 or more ACE v. 0	3.6 (0.3-49.3)	0.9 (0.2-4.6)	1.5 (0.3-7.6)
Experience 3 or more ACE v. 0	1.6 (0.0-90.8)	11.4 (1.8-73.6)*	0.53 (0.1-4.2)

Age at which adverse childhood experience begin to have effect in predicting onset of a DSM–IV disorder

Table 5 shows the results of a survival analysis to predict the age at onset of DSM–IV disorders. Even though not significant, the effect of a childhood experience of neglect/abuse on the onset of DSM–IV disorders was more prominent between the ages of 4 and 12 years and thereafter began to wane. The reverse was the case for the effects of parental loss and parental psychopathology; the effects were not significant between the ages of 4 and 12 years but became so when respondents reached 25 years of age.

Table 5

Age at which the adverse childhood experience (ACE) begins to have an effect in predicting DSM–IV disorder onset^a

	4-12 years age group OR (95% CI)	13-24 years age group OR (95% CI)	25+ years age group OR (95% CI)
Parent death	1.6 (0.3-8.7)	1.8 (0.3-11.4)	4.9 (1.0-24.1)*
Other parent loss	1.4 (0.2-8.2)	0.70 (0.1-5.4)	0.6 (0.1-2.2)
Parent mental health or substance use disorder	4.0 (0.7-23.4)	3.8 (0.6-26.5)	13.9 (2.0-96.0)*
Family violence/criminal behaviour	0.1 (0.0-0.5)	0.6 (0.1-3.7)	0.2 (0.0-1.8)
Neglect/abuse	2.1 (0.5-7.5)	1.6 (0.5-5.0)	0.6 (0.3-1.2)
Other adversity	0.5 (0.2-1.6)	0.4 (0.1-1.5)	0.4 (0.1-2.1)
Experience 2 or more ACE v. 0	1.9 (0.1-33.4)	3.7 (0.2-61.8)	10.0 (0.8-126.7)
Experience 3 or more ACE v. 0	3.4 (0.1-247.1)	3.5 (0.0-555.3)	< 0.001 (< 0.001-0.011)

Main findings

To our knowledge, this is the first study of family-related adverse childhood experiences in relation to multiple psychiatric outcomes in adulthood from Sub-Saharan Africa. The results we present indicate that a substantial number of people enter adulthood with significant adverse experiences in their past. Almost half of the respondents in this survey reported exposure to at least one adverse childhood experience occurring within the family context and about a third had been exposed to multiple adverse childhood experiences. These rates are much lower than those from the US National Comorbidity Survey, in which at least one adverse childhood experience was reported by 74.3% of the respondents and multiple experiences reported by more than half of the sample. ^{Reference Kessler, Davis and Kendler9} This difference in rates can partly be accounted for by differences in the adversities considered. The present study focused on experiences occurring within the family context, whereas the US National Comorbidity Survey reported a broader range of adversities. Our results are comparable to a prevalence of 52.1% reported by Felliti et al ^{Reference Felitti, Anda, Nordenberg, Williamson, Spitz and Edwards3} in the Adverse Childhood Experiences Study, where broadly similar categories of experiences were examined. Differences in estimates of adverse childhood experiences between studies may of course reflect not just the range of adversities explored but also the likelihood of the occurrence of specific adverse experiences. It is conceivable that social factors, including those relating to the structure of family in African and non-African settings, will have a bearing on the occurrence of adverse childhood experiences and that cultural expectations may determine which events individuals exposed to them would consider as being adverse. The traditional extended family system may help in protecting children from certain adverse experiences. For example, the occurrence of physical abuse and violence are probably less when people live together in large families, also divorce rates are low in traditional African settings. Although there is speculation that the rates of adverse experiences and traumatic events could be higher in children from low- and middle-income countries, ^{Reference Connor and Butterfield26} there is as yet no empirical data to support this claim. In accordance with the few previous studies that have examined a wide range of adverse events, exposure to one such experience was found to increase the likelihood of experiencing another. ^{Reference Felitti, Anda, Nordenberg, Williamson, Spitz and Edwards3,Reference Anda, Croft, Felitti, Nordenberg, Giles and Williamson7,Reference Chapman, Whitfield, Felitti, Dube, Edwards and Anda8,Reference Dube, Anda, Felitti, Edwards and Croft27}

In this study, when the effects of adverse childhood experiences on developing any DSM–IV psychiatric disorder was considered, most associations were null in the bivariate and multivariate models and all were null in survival models where the presence of comorbidities and clustering of adversities were accounted for. There are a number of possible explanations for this observation. First, it is likely that the power to detect significant bivariate associations remained low in our data even after grouping together the adverse childhood experiences. In particular, the numbers of respondents who met diagnostic criteria in the various DSM–IV disorder categories were small. ^{Reference Gureje, Lasebikan, Kola and Makanjuola17} Second, attenuation of association on multivariate modelling may reflect a common observation that the association of adverse childhood experiences to adult psychiatric disorders is likely due to the additive effect of experiencing multiple adverse experiences. Thus, in the US National Comorbidity Survey, whereas 67% of the odds ratios following bivariate analysis were statistically significant, only 32 and 15% were significant on multivariate and survival analysis in which adjustment was made for comorbidities and overlap among adversities respectively. ^{Reference Kessler, Davis and Kendler9} Mullen et al ^{Reference Mullen, Martin, Anderson, Romans and Herbison28} noted a considerable overlap in the occurrence of sexual abuse and family dysfunction and the difficulty in ascertaining whether child sexual abuse can actually act as an independent predictor of adult psychopathology. Third, considering that only a limited number of adverse experiences were assessed in this study, the possibility that other experiences not accounted for here might also be in operation cannot be ruled out. There might be other adversities specific to this culture and related to child-rearing practices or circumstances peculiar to children growing up in impoverished households which were not included in the study instrument.

Parental psychopathology stood out as significantly increasing the likelihood of developing a DSM–IV disorder in bivariate analysis and this association held even in the multivariate additive model, but there was attenuation when clustering of this adversity with other adversities was taken into account. The association between parental psychopathology and mental health disorders has been demonstrated in some earlier studies. For example, Pirkola et al ^{Reference Pirkola, Isometsa, Aro, Kestila, Hamalainen and Veijola11} reported that paternal psychopathology was associated with male depressive disorders and maternal mental health disorders with female depressive disorders, whereas maternal alcohol problems were associated with alcohol use disorders in both genders. Also, in the US National Comorbidity Survey, Kessler et al ^{Reference Kessler, Davis and Kendler9} reported that parental psychopathology, especially maternal psychopathology, was a risk factor for a broad range of adult mental health disorders. In that study too, as in the current one, there was a substantial attenuation of this association when other adverse childhood experiences were controlled for.

Although biological propensities cannot be ruled out in the association of parental psychiatric disorders with mental health disorders in adulthood of their offspring, the fact that the effects were ameliorated when other adverse childhood experiences were controlled for suggests that the presence of psychiatric disorders in parents probably increases the individual's likelihood to experience other adverse childhood experiences; which in turn makes the onset of mental health disorders in adulthood more likely. Up to 62% of respondents reporting parental mental health or substance use disorders reported at least one other adverse experience. Substance use disorders were more likely to occur among individuals who had experienced family violence and neglect or abuse in their childhood. These are the adversities that most likely result in low parental involvement in the upbringing of their children. Some other authors have proposed that children from such home environments probably have increased access to alcohol and increased opportunity to drink, thus placing them at an increased risk of earlier age at onset of drinking and increased likelihood of subsequently developing an alcohol use disorder in adulthood. ^{Reference Kim, Viner-Brown and Garcia29,Reference Rothman, Edwards, Heeren and Hingson30} Interestingly, loss of parents from death, separation or divorce was not linked to adult psychiatric disorders in this sample. This is at variance with earlier reports that loss events, especially parental separation/divorce, is a strong predictor of adult mental health disorders. ^{Reference Oakley Browne, Joyce, Wells, Bushnell and Hornblow31,Reference Noorikhajavi, Afghah, Dadkhah, Holakoyie and Motamedi32} Children in this culture are probably protected from the adverse consequences of parental death or separation by the availability of surrogates within the extended family network who take over the care-giving roles and responsibilities of the parents when such losses occur. It is striking that although parental death did not show a significant relationship to adult mental health disorders in the entire group, there was a significant association for disorders with onset at age 25 years and over. Although this is in agreement with previous suggestions that the impact of major childhood adversities persist well into adult life, possibly by producing a scarring effect that persists beyond the immediate period of the adversity, ^{Reference Chapman, Whitfield, Felitti, Dube, Edwards and Anda8} it probably also supports our impression that children with such losses are protected from the possible consequences early in life but the protection becomes attenuated in adulthood thus exposing the vulnerability of the victim.

Limitations

Our results are to be considered in the context of the study's limitations. Our assessment of the sexual abuse component of the abuse/neglect category did not include questions that enable us to state explicitly whether the report of sexual abuse was perpetrated by a family member and also excluded those who reported one or two episodes of sexual abuse. Previous studies suggest that extrafamilial sexual abuse can be distinguished from intrafamilial sexual abuse by the observation that the former is more likely to occur as a single episode whereas the latter is more often multiple in its occurrence. ^{Reference Dube and Hebert24,Reference Garba, Lampe, Borsos, Balla, Poka and Olan25} However, it is unclear whether this assumption applies in the environment in which our study was conducted. History of adverse childhood experience was obtained by retrospective recall. This is unavoidable and similar to the approach of other studies. Recalling events that might date back several decades is open to limitations of human memory and can be prone to errors. There is however evidence that retrospective recall of major childhood experience has validity. ^{Reference Hardt and Rutter33} The possibility nevertheless remains that current mental status may colour the reporting of past experience. However, the fact that no specific or unique association was found with mood disorders, which may be expected to more likely lead to a biased recall of negative experiences, would suggest that the associations reported here are probably not likely to have been differentially affected by the current mental status of the respondents.

Another important consideration is the fact that some index of psychopathology may have been missed. It is possible that the study instrument (CIDI 3.0) only captures some but not all the important variance that is germane to our interest because the concepts and phrases used to describe mental syndromes may differ in our cultural setting from those developed for use in Western cultures. Earlier reports form the World Mental Health surveys have reported lower rates of mental health disorders in low- and middle-income countries compared with high-income countries. ^{Reference Demyttenaere, Bruffaerts, Posada-Villa, Gasquet, Kovess and Lepine34} Factors accounting for the disparities in the rates of DSM–IV disorders in cross-national studies should be a focus for future surveys. There is evidence that the same instrument may perform differently in different age groups even in the same culture, ^{Reference Gureje, Kola and Afolabi35} and that estimates obtained using semi-structured clinician-administered interviews may be substantially different from those obtained using lay-administered fully structured interviews. ^{Reference Phillips, Zhang, Shi, Song, Ding and Pang36} Cultural distinctions are also known to occur in the perception and interpretation of adverse experiences and in the expression of response to the events.

Implications and future research

Our results highlight the fact that children growing up in a society that is still largely traditional and in which the extended family system remains the rule are also prone to experiencing adversities that are common in societies with a more nuclear family system. Along with problems associated with poverty there is also evidence of various forms of neglect and abuse. These adversities are not likely to be without consequences. Even though our study has found only a limited number of positive associations between adverse childhood experiences and adult mental health disorders, we believe that children who survive the difficulties of growing up in a society where more than 150 out of every 1000 children fail to reach the age of five may nevertheless be left with the scars of abuse, poverty and neglect that put them at elevated risk of mental health disorders in adulthood. Future studies should broaden the range of adversities explored, examine a more broadly defined spectrum of psychiatric problems and combine the use of emic ascertainment procedures with the decidedly etic approaches that current interview schedules and classificatory systems permit.