L ONGITUDINAL A NALYSIS

The analyses of the previous section show a continuous decline of union density in Switzerland between 1999 and 2011. Exploiting the longitudinal nature of our data, in this section we investigate the reasons behind this decline. In which ways can the union den-sity of a country vary from a year to another? We defined union density as the ratio between the number of wage-earners that are union members and the total number of wage-earners in a given year. Unions can act on the value of this indicator through two mechanisms. The variations from one year to another are influ-enced by the number of new union members and by the number of individuals that do not leave the membership status. In other words, unions’ strategies act on union density through the recruit-ment of new members and through the retention of those already members. The decline of union density we observe is either the product of a non-high enough contingent of new members or the consequence of a decreased duration of membership or a cumu-lative effect of both trends.

The study of Daniel Oesch (2012) is the only one investigating the issue for the Swiss case. Comparing the explanatory power of the number of outflows and the number of inflows in 70 union locals between 2006 and 2008, he shows that net changes in union membership are primarily determined by the number of inflows rather by the number of outflows. The success of a union is more

influenced by its capacity to attract new members rather than by the retention of old ones. The author argues that the result can be explained by the fact that the outflows are mostly related to events, such as job change, that are independent of unions’ efforts. On the contrary, the inflows are heavily determined by unions’ recruit-ment strategies and these are the fundarecruit-mental force that explains the differences in terms of net changes in the number of union members across unions. The results also show that the evolutions of the labor market context do not represent a key determinant of the membership trends in a union.

In our case, we analyze the effect of inflows and outflows on the diminishing union density level for the whole population of Swiss union members. How can we operationalize these two mechanisms? A straightforward measure of the recruitment ca-pacity of unions may be represented by the number of wage-earn-ers that become union membwage-earn-ers in a given year. On the other hand, the retention capacity of unions may be represented by the mean duration of union membership of individuals that become members. But how do we compute the mean duration of mem-bership? By definition, the mean duration is a longitudinal concept that can only be measured on an interval of years and not for a single year. One idea may be to compute at different points in time the ratio between the number of years an individual spends as wage-earner and union member and the number of years he spends as wage-earner. Unfortunately, this computation with the data at our disposal would be possible only for individuals that we observe since the beginning of their trajectory as wage-earners.

These are only those that are still completing their education dur-ing their first participation in the SHP or that achieved their form-ative path in the previous year. Such a restricted focus would ob-viously limit the interest and the external validity of our analyses.

A more appealing strategy is to focus on the number of years spent as union members by Swiss wage-earners during different time intervals. For example, we could compute the mean mem-bership duration between 1999 and 2004 and between 2006 and 2011 (the interval 2005-2010 cannot be taken into account since

we do not have data on union membership for 2010). The crucial condition is that the length of the time-intervals has to be the same. Also, the intervals should not be too short in order to be able to take into account the presence of spells long enough to measure unions’ retention capacity. Intervals of only two years, for example, would lead to consider all membership durations higher than one year the same way. The 1999-2004 and 2006-2011 inter-vals are good in this respect, but they are limited from another point of view. With 13 years of data, they allow us to compare only the change in the duration of membership between two pe-riods. We would like to find a way that gives us more time points of comparison in order to observe a more gradual evolution, while still keeping the advantages of these intervals. Our strategy is to analyze the evolution of the duration of union membership on 6-year shifting time-windows. More precisely, we examine the evo-lution of the duration of union membership on the following time-windows: 1999-2004, 2000-2005, 2001-2006, 2002-2007, 2003-2008, 2004-2009 and 2006-2011 (2005-2010 is excluded be-cause of missing data in 2010). Each time-window is distinguished from the previous one by a shift of one year in the observation interval. The strategy provides a longitudinal analysis of the evo-lution of the mean duration of union membership, while still giv-ing an evolution year after year. Havgiv-ing illustrated the advantages of shifting time-varying windows, in the following two sub-sec-tions we describe precisely how we exploit them to examine the evolution of the recruitment and retention capacity of Swiss un-ions.

2.4.1AT LEAST ONCE MEMBERS

Before turning to the regression analysis, we give some descriptive statistics on the number of wage-earners that become at least once members between 1999 and 2011. The union density we defined in sub-section 2.3.1 is a cross-sectional indicator of the proportion of wage-earners being union members. We extend it here to the longitudinal context by interesting ourselves into the proportion

of individuals that become at least once members between 1999 and 2011. However, in a longitudinal context, the definition of the population of interest is not univocal as in the cross-sectional case, where the focus is on individuals that are wage-earners in a given year. If we consider the percentage of individuals that become at least once members, while being wage-earners between 1999 and 2011, what is our population of interest? We could focus on those individuals that participated in all waves of the SHP and were marked at least once as wage-earners. In that case, our data show that 47.94% of such individuals became union members at least once between 1999 and 2011. If we focus on a more restricted population, analyzing only those individuals that participated in all waves of the SHP, while being wage-earners in all of them, this percentage increases to 63.02. Such indicators are certainly at least partially affected by an attrition problem. Nevertheless, they shows that, despite the decline of union density, the individuals that serve themselves at least once of the services provided by un-ions remain extremely important. In other words, unun-ions still play a very important role for wage-earners, even though the majority of them are not continuously affiliated.

We can now turn to a more formal analysis of the evolution of the recruitment capacity of Swiss unions between 1999 and 2011.

In order to be able to compare directly the results with those on the duration of membership, we focus on the same shifting time-windows described above. Therefore, we have 6 time points of data. More precisely, for each time-window, we create a binary variable that takes the value 1 if the individual becomes a union member by being at the same time a wage-earner in one of the years of a time-window and 0 otherwise. The main independent variable we use, represented by the last year in each time-window, is a set of time dummies identifying each time-window. The values of the control variables included in the regressions are also those appearing in the last year of each time-window. As we will moti-vate in sub-section 3.4.3, in this work and in the models of this particular section we chose to treat as linear the relationship of

interest even though the dependent variable is binary. We thus es-timate a linear probability model. The relationship we model can be represented by the following functional form:

𝐚𝐭 𝐥𝐞𝐚𝐬𝐭 𝐨𝐧𝐜𝐞 𝐦𝐞𝐦𝐛𝐞𝐫_𝐢𝐭 = 𝛂 + 𝐭𝐢𝐦𝐞 𝐝𝐮𝐦𝐦𝐢𝐞𝐬_𝐢𝐭^′𝛃 + 𝐜𝐨𝐧𝐭𝐫𝐨𝐥𝐬_𝐢𝐭^′𝛄 + 𝛍_𝐢𝐭 𝒇𝒐𝒓 𝒊 = 𝟏, 𝟐, … , 𝑵 𝒂𝒏𝒅 𝒕 = 𝟏, 𝟐, … , 𝑻 (𝟐. 𝟓)

We estimate three nested models by OLS (giving thus a pooled OLS estimator) with an increasing set of control variables. The first type of model contains only the key independent variable and one indispensable control variable. In order to account for the number of years in which an individual has actually the possibility of becoming a union member, it is crucial to include as control a variable that represents the number of waves an individual has participated in the SHP as wage-earner in each time-window. In a second model, we add as controls the main socio-demographic characteristics (sex, age, education, nationality and canton of resi-dence). In a third one, we add a further set of control variables that capture the effect of the flexibilization of the labor market (indeterminate or time-limited contract, full- or part-time work, private or public sector, NOGA sector, company size and job and/or employer change in the last 6 years, i.e. the length of the windows under examination). The observations in each time-window are weighted using the cross-sectional weights of the last year of the time-window since only that year distinguishes the given time-window from the previous one. Finally, we use cluster robust standard errors that allow obtaining correct test statistics for arbitrary forms of heteroskedasticity and serial correlation within the observations of each individual.

The results are presented in table 8.2, section 8.2 of the appen-dix chapter. The first model shows a continuous and significant diminution of the chances of becoming a union member at least for a year in more recent time-windows. For example, the average wage-earner has 4.1% less chances to become a union member in the interval 2004-2009 than in the 1999-2004 period. Only the last

window shows a slight inversion of the trend. Interestingly, the estimates we obtain in the two other models by increasing the number of control variables are almost equivalent to those in the first one. Neither the demographic changes nor the evolutions served in the labor market modify the diminishing trend we ob-serve in unions’ recruitment capacity.

2.4.2DURATION OF MEMBERSHIP

Focusing on the duration of membership, we start again by providing some descriptive statistics for the period between 1999 and 2011. Unfortunately, since the majority of the individuals in-terrupt their participation in the SHP at some point, we cannot give reliable information on the mean duration of continuous ep-isodes of union membership. However, for each individual, we can at least compute the ratio between the number of years he belonged to a union being at the same time a wage-earner and the number of years he worked as wage-earner during his participa-tions in the SHP. The mean of this ratio for all participants of the SHP is equal to 0.211. This means that, on average, the typical wage-earner in Switzerland spent 0.211 * (2011-1999 + 1) = 0.211

* 13 = 2.743 years as union member between 1999 and 2011. If we redo the same count for individuals that became at least once members over the period under examination, the mean of the ra-tio is equal to 0.559, which implies a mean of 7.267 years spent as union member between 1999 and 2011. As in the previous sub-section, these analyses are certainly affected by an attrition prob-lem. They are however interesting in order to get at least a broad image on the number of years Swiss wage-earners spend as union members.

We now turn to a more formal analysis of the evolution of the duration of union membership in Switzerland between 1999 and 2011. We employ the same regression models of the previous sub-section:

𝐝𝐮𝐫𝐚𝐭𝐢𝐨𝐧 𝐦𝐞𝐦𝐛𝐞𝐫𝐬𝐡𝐢𝐩_𝐢𝐭 = 𝛂 + 𝐭𝐢𝐦𝐞 𝐝𝐮𝐦𝐦𝐢𝐞𝐬_𝐢𝐭^′𝛃 + 𝐜𝐨𝐧𝐭𝐫𝐨𝐥𝐬_𝒊𝒕^′𝛄 + 𝛍_𝐢𝐭 𝒇𝒐𝒓 𝒊 = 𝟏, 𝟐, … , 𝑵 𝒂𝒏𝒅 𝒕 = 𝟏, 𝟐, … , 𝑻 (𝟐. 𝟔)

We replace the dependent variable with the number of years spent as union member for each wage-earner that has been at least once a union member within a given time-window. This restriction (having been a union member at least once within the time-win-dow) is crucial since, otherwise, we may observe a decrease of the duration of union membership for all wage-earners because of the diminution of individuals that become members at least once. The objective here is on the contrary to see whether the duration of membership decreases for individuals that become members at least for a year within a given time-window.

The results are presented in table 8.3, section 8.2 of the appen-dix chapter. In all three models, we do not observe a significant evolution of the number of years spent as union members in more recent time windows in comparison with the 1999-2004 period. In other words, the duration of union membership for wage-earners that actually become members at least once is not subject to a change between 1999 and 2011. Surprisingly, as in the previous set of models, the change of the profile of the average wage-earner and the evolutions of the labor market do not seem to have an impact on the evolution of unions’ retention capacity.

What do the results of these two sets of regressions models imply? They lead us to the same conclusions described by Daniel Oesch (2012). The decrease of union density in Switzerland is re-lated to a decreased capacity of unions to recruit new union bers and not to a diminution in the mean duration of union mem-bership. Also, the demographic and economic evolutions we ob-serve between 1999 and 2011 do not influence the trends.

One may wonder whether the results we obtained are depend-ent on the particular strategy of time-varying windows we adopted or also on the 6-year length of the windows we chose to consider.

Additional analyses show that similar results can be obtained with shorter or longer time windows. Also, similar conclusions, even though based on a lower number of time intervals, can be pro-duced by considering separated time-windows as described at the beginning of the section.

2.5 I

What are the implications of the analyses of this chapter? The cross-sectional analyses of the third section confirm the presence of a declining trend of union membership in Switzerland. How-ever, they also highlight that the declining trend does not concern the same way all categories of wage-earners. In particular, union density decreases sharply for traditional profiles of union mem-bers (men, old wage-earners, individuals with a secondary educa-tion,…), while the decrease is much less pronounced for some emerging profiles of wage-earners (part-time workers and women in particular).

Is the decline related to a lower inflow of new members or to a more important outflow of wage-earners that become members?

The regression analyses of the previous section show that the de-clining trend is related to a decreased recruitment capacity of Swiss unions rather than to a decrease in the mean duration of member-ship. If the argument exposed in Oesch (2012) holds, implying that the level of inflows in unions is mostly determined by unions’

strategies, while the retention of old members is mostly deter-mined by external events, these conclusions are rather positive for the future of Swiss unions. If the success of a union is mostly de-termined by its attraction strategies rather than by uncontrollable evolutions, in particular the changes in the labor market, there is still hope that the declining union density trend may be reversed.

In particular, such a change can be expected if unions will be ca-pable of increasing their attractiveness with respect to the emerg-ing categories of wage-earners. As we described in sub-section 2.1.3, efforts in this direction are already made by Swiss unions.