Tag Archives: migration

Push and pull?

Having been confronted with the “pull” doctrine now many times, I went for further literature. The best summary that I have found is by the European Asylum Support Office 2016

On the conceptual level, there are serious limitations with the commonly used (yet often critiqued) push and pull framework as an explanatory tool for migration decision-making processes … it makes strong assumptions about the way individuals respond to stimuli; it presumes that an individual can make cost/benefit decisions based on full information, in markets tending to a general equilibrium, far from the complex reality of human mobility. As such, the model fails to explain why, for instance, people respond differently to the same ‘push’ and ‘pull’ forces, and why emigration and immigration occur simultaneously in the same area.

There seem to be many more limitations than currently assumed.

factors explaining migration 1) often originate in the household/community/country of origin (e.g. unemployment, gender discrimination, conflict), while factors influencing migration 2) are more likely to be destination-specific (e.g. presence of co-ethnic community members, perception of the country as having a permissive asylum regime, language similarities) or process- specific (e.g. a smuggler has chosen a destination).

Another key issue, is the high death toll that is of course known to refugees.

Studying migration flows across the Mediterranean, particularly along two routes (the western and central Mediterranean routes), Altai Consulting found that social, political, and economic instability inspired migration flows but that individuals fleeing greater threats to their personal security were willing to traverse more dangerous and uncertain migration routes.

So we are dealing with

  • Socio-economic factors
  • Political factors
  • Demographic factors
  • Historical, cultural and geographic factors
  • Environmental factors
  • Migration policy factors
  • Economic factors in the asylum destination choice
  • Summary of convergence/divergence trends

The report shows the relevance of migrant networks in facilitating asylum migration movements and influencing migrants’ destination choices. Going back even to an earlier report of migration direction in Science, I can’t find any evidence for any pull effect.

Guy J. Abel and Nikola Sander. Quantifying Global International Migration Flows. Science 2014; 343:6178


Aug 4, 2023

There is a new time series study in Sci Rep by Alejandra Rodríguez Sánchez aggregating counts of arrivals, pushbacks, and deaths adjusting for various known drivers of irregular migration via the Central Mediterranean Route


A comparison of the observed and predicted counterfactual time-series in the post-intervention periods suggest that pushback policies did affect the migration flow, but that the search-and-rescue periods did not yield a discernible difference between the observed and the predicted counterfactual number of crossing attempts.

So there is push but no pull.

Does a healthy worker effect explain the allergy protection” at Bavarian farms?

Unfortunately most studies in the farming environment do not report the prevalence of parental history. Neither did they report the effect size of parental  genetic risk in the farming population. This is, however, a critical issue as the so called healthy worker effect (HEW) may be a rather trivial explanation of the results.

Specifically, it is a sampling bias: the kind of subjects that voluntarily enroll in a clinical trial and actually follow the experimental regimen are not representative of the general population. They can be expected, on average, to be healthier as they are concerned for their health [or as ill people already dropped out]

At least Braun-Fahrländer 1999 reported that allergic parents were seen much less at farms.  Consecutively history of allergy at farms is no more a risk factor as it is otherwise reduced compared to the general population – no diseased parent, no increased risk.  So lets see if there are  any further studies in adults?

I know of three studies (plus a review Le Moual N 2008).

Leynaert 2001 showed only a slightly reduced prevalence of “allergy” (39.1% vs 41.5%, NS). Her table 4 is most interesting. The association started only after year 1960 which points towards severe misclassification as far as the analysis is not stratified by year of birth.

Remes 2002 showed a dose dependent effect decline between farming (36.2%) and controls (31.6%, P=0.075),

Perkin 2006 also found some significant lower prevalence in farmers 47.3% versus 57.7%, P<0.001. HWE is therefore likely.

I found further six studies (Thelin 1994, Braback 2006, Chenard 2007, Thaon 2011, Elholm 2013 and Spierenburg 2015) that examined in detail a possible relationship of HWE, allergy and farming. Unfortunately the examination period in five of these studies is too short to make any conclusion while Braback 2006 seems to be the only reliable study.

Source: Braback 2006

From this study, we can safely conclude, that there is a significant HWE.


Addendum 22 Nov 2019

It seems that I missed some papers on HWE and farming.

Timm 2019 is a hard to understand cluttered 3 generation study of unclear asthma  type. Point estimates of parental asthma on farm upbringing are not really a measure of HWE – shuffling exposure and outcome distorts temporality. In contrast to the interpretation of the authors, I see a clear effect if both parents are born on a farm and one parent has asthma. The RR drops here to 0.33 that their child will be raised on a farm.

Vogelzang 1999: 400 pig farmers, X-sectional point estimates, not a  real HWE study, although HWE offered as explanation.

Health-based selection of nonasthmatics for pig farming, which tends to mask a work-related hazard for asthma, is offered as an explanation for these results.

Eduard 2015: compares asthma prevalence of 313 Danish farm children to their 518 sibs (which is identical) but useless, as affected parents would basically dropout all children.

There is even a second comparison of Norwegian farmers with a clear effect. Instead of comparing the early retired farmers with their respective age cohort they invented a c complicated quantile logitic regression in 4 year intervals. Detailed model parameter and significance levels are missing.

At least the conclusion was

A healthy survivor selection was observed in Norwegian farmers, but it was too small to fully explain the reduced risk of asthma observed in this population. A strong selection effect was observed among farmers who had changed production type

will be continued…