Indigenous peoples of North America

Although there is considerable literature on rates of psychiatric morbidity, comparisons with the general population that use the same instruments and methodology are more limited. A recent meta-analysis covered 19 studies conducted in the Americas, all but three of which came from North America.^{Reference Kisely, Alichniewicz and Black4} Of these, ten studies were from the United States and six from Canada. For inclusion in the review, studies had to have data on similar controls. Ways of increasing comparability included checking for similarities in demographic characteristics, stratification by age or gender, and the use of standardisation and/or multivariate analyses. The focus of the review was on common mental disorders but if any of the included papers also reported on alcohol and substance use, these data were included in any meta-analysis.

Rates of alcohol and substance use were consistently higher in all the Indigenous populations surveyed, as was the prevalence of post-traumatic stress disorder (PTSD). By contrast, there were no differences in the rates of other common mental disorders when compared with the general population of similar age or gender, and using the same instruments (Fig. 1). These included the 12-month prevalence of depressive, generalised anxiety and panic disorder. Findings were similar irrespective of geographical region (Fig. 1) In five studies of depression that adjusted for further socioeconomic variables, any effect was to generally lessen the association between Indigenous status and psychiatric morbidity, not increase it.^{Reference Kisely, Alichniewicz and Black4} This applied to both 12-month prevalence and lifetime rates. By contrast, rates of PTSD remained elevated in the three studies that adjusted for similar sociodemographic variables.^{Reference Kisely, Alichniewicz and Black4}

Fig. 1 Comparing the 12-month prevalence of common mental disorders. IV, inverse variance.

There were similar findings in a further meta-analysis of studies from Australia and New Zealand, although the pattern was less clear because of fewer studies.^{Reference Black, Kisely and Alichniewicz5}

There may be a number of explanations for these findings. One might be that the instruments or diagnostic criteria used in these studies may not accurately reflect psychiatric morbidity in Indigenous populations. On the other hand, many of the studies used culturally validated forms of standardised assessment measures, and it is unclear why instruments would fail to detect disorders such as major depression, but not others such as PTSD where rates were significantly elevated.^{Reference Kisely, Alichniewicz and Black4,Reference Black, Kisely and Alichniewicz5}

Another is that risk factors for PTSD or alcohol and substance use may differ from those for depression. Possibilities include early removal from families and cultures of origin, as well as subsequent institutional and domestic abuse. In one national survey, nearly a quarter of Indigenous Australians were the victim of physical violence in the previous months, including 8.1% who had experienced physical violence on more than one occasion.⁶ In half of cases, the perpetrator was a family member. Fifty per cent had been the witness to violence and just under 40% reported a recent death of a family member or close friend.⁶ Similar factors apply to the increased rates of suicide reported in Indigenous people worldwide. Common mental health disorders may also be underpinned by different constructs. According to Krueger's three-factor model, generalised anxiety and depression represent distinctly different aspects of internalising when compared with PTSD, whereas externalising patterns are associated with alcohol and substance use disorders.

In other circumstances, Indigenous culture may be protective. For instance, Indigenous Australians and New Zealanders report less psychiatric morbidity when they form a higher proportion of the population despite other markers of social deprivation, possibly because of connection to culture and traditional lands.^{Reference Nasir, Toombs and Kondalsamy-Chennakesavan7,Reference Houkamau and Sibley8} Elsewhere, a Canadian survey found that 70% of First Nations adults living on reserves felt in balance physically, emotionally, mentally and spiritually.^{Reference Khan9} Indigenous people may therefore have higher rates of psychological distress because of factors unrelated to ethnicity, but experience lower rates of disorders because of cultural connection or density.

Two unique communities in Nova Scotia

There are also non-Indigenous minority communities with long histories of continued settlement and thus no experience of recent internal or external migration. Two are in Nova Scotia, a province on the eastern seaboard of Canada. Originally occupied by the Mi'kmaq, European settlement dates back to 1605. This rich history has led to a number of unique communities. One is the African Nova Scotian community of Preston, whose inhabitants are descended largely from refugees from the USA who settled in many areas of the province from 1813 to 1816.^{Reference Kisely, Terashima and Langille10} Another is the community of Clare, a community whose population is predominantly Acadian (French) who remained in the Province following the large-scale deportation of French settlers by British authorities between 1755 and 1764.^{Reference Langille, Rainham and Kisely11} Given the 200-year history of both communities in the province, immigration would not be a contributing factor to either psychiatric morbidity or health service use. In the case of African Nova Scotians, neither would language.

As in other parts of Canada, all Nova Scotian residents are entitled to in-patient or out-patient care that is free at the point of delivery. Patients are seen at publicly funded facilities, or by private psychiatrists and general practitioners in the community who then bill the provincial health plan. Province-wide data on health service use are therefore available for both primary care and specialist services.

In both cases, treated psychiatric morbidity was compared with other communities matched on other relevant sociodemographic factors, as well as the province as a whole. For instance, Clare is predominantly rural, so comparison Anglophone communities were selected based on similar rurality. Incidence rate ratios relative to Nova Scotia's entire population were calculated for each area and the comparison, using indirect age and gender standardisation.

For both African Nova Scotians and Acadians, there was a low level of contact with psychiatric specialists compared to the province as a whole.^{Reference Kisely, Terashima and Langille10,Reference Langille, Rainham and Kisely11} By contrast, depending on the comparison group, there were higher rates of family physician visits and hospital admissions. However, this result was attenuated when comparisons were made with groups of similar rurality.^{Reference Langille, Rainham and Kisely11}

The findings on Acadians are mirrored by studies of Francophones elsewhere in Canada as well as of international comparisons of different ethnic and language groups.^{Reference Chartier, Finlayson and Prior12,Reference Vasiliadis, Lepnurm and Tempier13} After adjusting for sociodemographic and economic factors, such as age, gender, education, income and place of residence, there was little difference in psychiatric morbidity as measured by community surveys or administrative data.^{Reference Chartier, Finlayson and Prior12,Reference Vasiliadis, Lepnurm and Tempier13} These factors rather than language per se appear to explain differences in the prevalence of disorders.^{Reference Vasiliadis, Lepnurm and Tempier13} This does not mean that these variables remain static. For instance, the role of Catholicism in defining francophone communities has diminished as they have become more secular.