>If I read it correctly, this means that union membership is an intervening
>(if not spurious) variable i.e. political preferences make people more
>likely to be union members, and that also affects their voting behavior
That's not what Freeman says (and for most workers, their preferences about unions are pretty irrelevant, given how few workplaces are organized). Here's his summary of his findings:
>There are five substantive findings:
>
>1. Exit poll data give a misleading picture of the trend in the
>union share of the electorate, and thus of the extent to which
>unions offset loss of density through get-out-the-vote campaigns.
>
>2. Current Population Survey voting supplements understate the union
>share of voters by excluding retirees and other non employed persons
>with union affiliation from their measure of union members. Counting
>non employed persons who claim union membership as union voters, the
>union share of voters is about 50% higher than the union share of
>workers.
>
>3. Union members are 10-13 percentage points more likely to vote
>than non-union members, but the union voting premium - defined as
>the difference in turnout between members and non-members with
>comparable characteristics - is much smaller: about 4 percentage
>points.
>
>4. Union members are 12 to 13 percentage points more likely to vote
>for a Democrat than are demographically comparable nonunion voters,
>but about half of this difference is due to union members holding
>favorable attitudes toward liberalism and the Democratic party. All
>but 2-3 percentage points of the difference arises prior to a given
>campaign.
>
>5. Three to four times more non-union than union voters hold very
>positive views of trade unions, suggesting that in an era of
>declining density a successful union political strategy depends on
>union ability to reach and influence these non-members.
Later on in the paper:
>AThe first two lines show that union members are more favorable to
>Democrats vs Republicans and toward liberalism vs conservativism.
>Addition of demographic characteristics ( age, gender, years of
>education, race, and household income) in column 2 increases the
>impact of unions on these attitudinal indicators. This reflects the
>fact that union members are older, more skilled, and are in the
>upper half of the income distribution, where persons have more
>conservative Republican leanings. *Unionism moves members to the
>left of where they would be given their socioeconomic status.*
>[asterisks indicate italics in original]
And the last paragraph:
>With respect to voting preferences, this study has found that union
>members are more likely to vote for a Democrat for the House or
>Presidency than demographically comparable nonunion voters, largely
>because union members have attitudes and voting inclinations
>favorable to the Democrats and to liberalism prior to a given
>campaign. From this perspective union political activity is more of
>an investment in long run political influence rather than delivery
>of votes in a particular election. Finally, this study has
>identified a sizable group of nonunion persons with pro-union
>attitudes that unions could potentially influence to maintain the
>union impact on elections, even though these persons cannot gain
>collective bargaining contracts.