It depends how you want to define "strength". Some correlational studies point to a stronger economy being associated with more diverse countries. Other studies point to a lower degree of social trust being associated with more diverse countries.
As I said in comments, people will read these according to their prior inclination, since there's probably no way to set up true controlled experiments in such matters, i.e. studies are observational. The first link mentioned for instance that
Causality can run both ways – countries that have a higher growth rate might attract more immigrants from a variety of origins, thereby increasing the degree of diversity. Therefore heterogeneity might be the effect rather than the cause of economic growth.
But nonetheless concludes that
The most conservative estimates suggest that a one percentage point increase in the growth rate of fractionalisation (polarisation) boosts per capita output by about 0.1 percentage points in developing countries.
The second link also cautions that
Following from the fact that the vast majority of existing studies are based on observational cross-sectional
data, the detected negative relationship ethnic diversity and social trust cannot be given a causal
interpretation. [...]
And provides some historical counter-trends
However, over a longer time span and across a broader set of countries, the relationship between ethnic
diversity and generalized social trust appears very heterogeneous with no immediately obvious trend (Ortiz-
Ospina & Roser 2019). Of course, the famous decline in social trust in the United States from the 1960s
onwards—a period of increasing ethnic diversity—fits the pattern, but also lends itself to several other
explanations (Putnam 2000). Yet, other countries have experienced marked increases in trust over the last
decades. Perhaps most strikingly, Denmark, a country that has diversified at a considerable pace since 1980,
saw a dramatic increase in generalized social trust—from 47% trusting others in 1979 to 79% in 2009—in this
period.
Nevertheless its main conclusion is that:
as a baseline result, across all studies, we observe a statistically
significant negative relationship between ethnic diversity and social trust of moderate size. On average, social
trust is thus lower in more ethnically diverse contexts. That being said, the rather modest size of the
relationship also implies that apocalyptic claims regarding the severe threat of ethnic diversity for social trust
in contemporary societies are exaggerated.
Regarding the comment, the authors of another study in this area comment/claim that
Moreover, one can also speculate about the formation of political economy vicious or virtuous circles emerging from the interaction between the different dimensions of immigration policy. Given that a highly skilled and more diverse immigration is not only economically more profitable but also better accepted by public opinions, it does not take much to imagine a scenario where quantity, quality and diversity of immigration interact to generate more prosperity.
Countries such as Australia, Canada and the US would seem to illustrate the virtuous regime quite well.
The opposite scenario combines weak, unskilled and poorly diversified immigration where each aspect reinforces the other.
Most European countries seem to fall into the second category. They are stuck in a low-skilled and low-diversity immigration trap. Increasing the size of this type of immigration flows will do little to increase prosperity of the receiving countries. Increasing the diversity and the size of high skilled immigration would help.
So if this is correct, there's no uniform effect of "first-generation migrants", i.e. it depends on who they are. (Generalizing from the US context might thus be erroneous, at least on this matter.)
Yet another article discussing the efffects of (low-skilled) immigration on "market imperfections and income redistribution" concludes that the (bad) effect of low-skilled immigration is overrated:
in two-thirds of the 20 [OECD] countries analysed, both high-skilled and low-skilled natives would benefit from a small increase in immigration from current levels. The average welfare gains from immigration are 1.25% and 1.00% for high- and low-skilled natives, respectively.
According to this analysis, the non-obvious difference in effects depends not as much on the immigrants, but on the host country's unemployment level:
The introduction of job creation by firms – an important feature of our framework – generates two important effects of immigration. In particular, if firms cannot discriminate between natives and immigrants in the search process, but can pay immigrants lower wages (as is the case in the data), then the presence of immigrants drives up the average return from job creation. This encourages firms to create more jobs, some of which will be filled by natives. However, if matches with immigrants are more likely to break (as implied by their larger unemployment rate), the expected return to job creation is lower and firms will create fewer jobs. Which channel dominates depends on the relative strength of each mechanism.
(Also note that the definition of skill in an immigration system often has origin-diversity implications.)
The conclusion that low-skilled or poor natives are beneficiaries of immigration nonetheless seems controversial, at least in the US, if we consider the effects of Asian and Latino immigration on African Americans, as conventionally described:
These relatively recent changes in the national origins of immigrants have converted the United States from a largely biracial society
consisting of a sizable white majority and a small black minority (together with a very small Native American minority of less than 1
percent) into a multiracial, multiethnic society consisting of several
racial and ethnic groups. This trend became discernible in the 1950s
but began to accelerate in the 1960s. By 1998, more than a quarter of the U.S. population designated itself as either black, Latino, or Asian.
The speed with which the Latino and Asian groups have been growing has meant that the proportion of African Americans in the racial
and ethnic minority population has been declining. By 1990, blacks
were no longer a majority of this population, making up only 48
percent of racial and ethnic minorities. By 1998, their share had
fallen to 43 percent. [...]
In general, the economic implications of immigration for African
Americans appear less than benign. The fact that gains in black economic status ceased during the high-immigration 1980s and 1990s,
after notable gains following passage of antidiscrimination laws and
adoption of affirmative action policies in the 1960s and 1970s, encourages the idea that immigration has done little to generate opportunities for economic advancement for native blacks. Moreover, this
conclusion is buttressed by the compilation of research evidence indicating that immigration appears to worsen slightly the already precarious economic positions of African Americans, especially those with a
high-school education or less. Thus, the racial and ethnic diversification of the United States population over the past three decades
brought about by immigration, a trend some analysts might have
thought would bring advantages to nonwhite minorities, including
blacks, seems, at least at this point in time, not to have improved the
economic status of African Americans overall; and given recent political and legal developments limiting affirmative action (Bowen and
Bok 1998), its current prospects for improving black economic status
may be even less than in the past.
Likewise
Using data from the 1960–2000 US
censuses, we find that a 10% immigration-induced increase in the supply of workers in a particular skill
group reduced the black wage of that group by 2.5%, lowered the employment rate by 5.9 percentage
points, and increased the incarceration rate by 1.3 percentage points.
So one thing that seems clear is that one can't really discuss the "native" diversity (e.g. in relation to economic outcomes) while ignoring immigration (and its diversity), i.e. two are probably not independent.
The strength of the relationship in the US seems controversial as well.
Citing a 2017 report from the National Academy of Sciences, the Washington Post reported that “low-skilled immigration did have small effects on wages of certain subgroups of native workers: high school dropouts, teenagers, low-skilled African American workers, and low-skilled Hispanics (immigrants and native-born), especially those with poor English skills.” But the Post also notes that according to the researchers, “over a period of 10 years or more, the impact of immigration on wages of native-born workers is ‘very small,’ and not enough to account for stagnant wages within those groups.”
And since this is an IT-oriented group of sites... From the NAP review, I'll quote the part relevant to that:
The possibility of natives changing occupation or field of study has been of particular interest in the context of immigrants’ effect on innovation. Consequently, a number of papers ask whether skilled immigration causes natives to leave or fail to enter STEM fields. Orrenius and Zavodny (2015) examined whether native-born bachelor’s students pick a science or engineering major. The covariates of interest measure the concentration of immigrants in college as well as the concentration of immigrants when the natives were of high school age, and the instruments are variants of the historical settlement pattern instrument. They found that the presence of immigrants deterred some native-born women from choosing a science or engineering major; this effect was not found for native-born men. Some evidence of native response to immigrants entering STEM fields was also found by Bound et al. (2015). Using a structural model, the authors estimated that native employment in computer science would have been 7.0-13.6 percent higher in 2004 absent increased immigration after 1994; they also found wages for computer scientists would have been 2.8-3.8 percent higher. However, they found that total employment in computer science would have been 3.8-9.0 percent lower. This is consistent with the possibility that immigration increased software innovation, although this is of course hard to measure. [...]
At least as measured by patents, immigrants do innovate considerably more than natives. Using the 2003 National Survey of College Graduates (NSCG), Hunt (2011) showed that among individuals with a bachelor’s degree or higher, immigrants are twice as likely to patent as natives, while Kerr (2007) documented the rapid rise from 1975 to 2004 of U.S. patents authored by U.S. residents with Indian and Chinese first and last names: from 2 percent to 9 percent of all patents for Chinese names and from 2 percent to 6 percent of all patents for Indian names. Kerr could not distinguish first and second generation immigrants, but this growth is nevertheless fundamentally fueled by immigration.
More specifically, the Hunt (2011) study showed that 0.9 percent of natives, compared to 2.0 percent of immigrants, had been granted a patent in the previous 5 years. One measure of the quality of these patents is whether they have been licensed or commercialized; 0.6 percent of natives compared to 1.3 percent of immigrants had licensed or commercialized a patent granted in the previous 5 years. All these differences were statistically significant. She also found that, conditional on having at least one patent, immigrants and natives had similar numbers of patents. [...] Hunt also investigated the source of the immigrant advantage and found that the immigrants’ edge was due to their being much more likely to have studied science or engineering as a highest degree and to a lesser extent to their having higher education than natives. Her comparison among immigrants and natives with similar fields of study and level of education did not yield any statistically significant differences in patenting.
