Educational Research - the Ethics and Aesthetics of Statistics

7 To Frame the Unframable: Quantifying Irregular Migrants’ Presence 99
related to estimating irregular migrants has not prevented policy makers from focusing
on this area. Paying lip service to unreliable figures is having far-reaching
consequences. Before approaching this issue, I will consider, what is said in these
reports and the conclusions that have been drawn from the findings.
7.2 Techniques for Estimating Irregular Migration Numbers
A lot of creativity is put into action to estimate numbers of irregular migrants. The
list of different techniques that can be used is long and varied. Without going too
deeply into the particularities of different techniques and the problems each presents
us with, an overview of methods is outlined here. Then attention is given to some
examples of the most widespread methods and how they are applied.
In general, there is a consensus on the classification of various techniques. Recent
reports of the Clandestino Project (Kraler & Vogel, 2008; Vogel & Kovacheva,
2008; Picum, 2009) and the Home Office (Woodbridge, 2005; Pinkerton et al.,
2004) all start from the distinction between ‘stocks’ and ‘flows’, in the line of earlier
research (among others Delauney & Tapinos, 1998; Pinkerton, McLaughlan,
& Salt, 2004; Jandl, 2004). This fundamental distinction is made in analogy with
data on legal migration and refers to different statistical concepts: stocks (e.g. of
irregular residents or migrant workers) refer to a number of people that are present
in a country at a particular point in time, while flows (e.g. of illegal entrants or
migrants ‘overstaying’) refer to movements during a certain period. Flow estimates
thus refer to the number of migrants crossing the border during a period
in time. Estimations are mainly based on border apprehension data or entry-exit
statistics. Given the volatile nature of migration flows, the scarcity of reliable indicators
and the dearth of appropriate methods for estimating flows, most efforts have
so far concentrated on estimating stocks rather than flows. Methods for estimating
stocks of irregular migrants can be divided into direct and indirect approaches.
Direct measurement is based on data that ‘captures’ the subject of research directly.
Numbers of irregular migrants taken from administrative statistics based on refusals,
infractions or regularisations are multiplied to estimate the total number in the population.
Indirect estimates do not rely on such data. They mainly start from general
data on the population to estimate irregular migrant numbers (e.g. by expecting
similar proportions of irregular migrants or calculating residues in official registers).
Direct estimation approaches can be further classified into multiplier methods
(among which simple multiplier models, capture-recapture models and models
using a comparison of administrative registers and random effect mixed modelling),
methods of self-identification and snowball sampling methods. Among the indirect
approaches, residual methods, demographic methods, subjective estimations
or indicator methods, econometric methods on the size and structure of shadow
economies, comparisons of immigration and emigration statistics, flow-stock methods
and methods based on indirect inferences can be distinguished. It is not the aim
here to provide an extensive discussion of all the methods mentioned above (for