Published online by Cambridge University Press: 27 January 2009
There has been considerable recent debate about the importance of local context as an influence on political attitudes and voting behaviour in Great Britain. Resolution of that debate has been difficult, because analytical methods have not been available with which to evaluate the relative importance of both individual voter characteristics and the characteristics of their milieux as independent correlates of attitudes and behaviour. The technique of multi-level modelling has been developed by educational researchers to do just that. It is introduced here and illustrated using data for the 1987 British general election. The preliminary results suggest that place clearly does matter as a component of the processes that influence voters' choices.
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6 An important third relevant spatial scale within Great Britain is country – England, Scotland and Wales. The latter two have particular political parties contesting all constituencies, along with the three that contest all, or virtually all, in Great Britain. For technical reasons, however, we are currently unable to incorporate this further scale in our multi-level modelling work, as current software can only estimate complex models (with random slopes) with no more than three levels.
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16 Throughout this article, age for each individual is measured as that person's deviation from the mean age for the entire sample.
17 See fn. 15 above.
18 This is an aspect of multi-level modelling that makes it particularly valuable for the analysis of British Election Study (BES) data. In the surveys conducted for the BES, the respondents are selected according to cluster sampling designs (as described in Butler, and Stokes, , Political Change in BritainGoogle Scholar, and Heath, et al. , How Britain Votes).Google Scholar This introduces spatial autocorrelation: people living in the same area within a constituency – in this case, a polling district, which is the sampling frame used – are more likely to be similar in their socio-economic characteristics, for example, than are people selected randomly from within the entire constituency. This introduces imprecision to the estimation of relationships at the individual level (between age and voting, for example): by explicitly including the constituencies as a higher level, multi-level modelling automatically overcomes the problems of mis-estimated precision that are inherent in a clustered, multi-stage sampling design.
19 The lines on the graph (a) in Figure 1c are drawn to extend from the minimum to the maximum age in each constituency, for it is good practice not to ‘predict’ beyond the range of the available data.
20 Paterson, L. and Goldstein, H., New Statistical Methods for Analysing Social Structures: An Introduction to Multilevel Models (London: Institute of Education, forthcoming).Google Scholar Their advice stems from educational research, and it may be possible to manage with a smaller sample if the contextual effects for constituencies are greater than those for schools.
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34 The places are indeed the observations, and the greater the number the better. Having many voters provides information on the relationships between response and predictor variables within a place, but many places are needed to estimate the differences between places.
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38 To avoid confusion, logits will be given in the text with decimal points; when transformed into proportions they are multiplied by 100 and given as percentages.
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40 As degrees of freedom increase, Z-ratios equate to t-ratios.
41 As indicated above, the level-1 variance is set to 1.00, so the autocorrelation coefficient is 0.88/(1 + 0.88) = 0.47.
42 In a perfectly designed and executed survey, these forty areas would indeed be the safest seats in the country for either the Labour or Conservative parties. There are few surprises in the list, indicating a generally representative sample, the exceptions being Thurrock, Walsall North, Tynemouth, Nottingham South, Renfrew West and Inverclyde, and Blyth Valley. In the case of Renfrew West and Inverclyde, it may seem odd that this was ‘the most pro-Labour place in the sample’, when in fact the Conservative party won the seat in 1983. The similar finding in Model B indicates that the place was the most pro-Labour, given the characteristics of its population. It should also be noted that the cluster sampling procedure used in the BES may have resulted in the selection of a polling district that was very unrepresentative of the constituency as a whole. This calls for further work which uses the polling district as one of the levels in a multi-level model, an approach which is as yet not possible due to the inability to estimate complex models at more than three levels with existing software.
43 The estimates are obtained by inserting the relevant data into the model. Thus, to take a complex illustration based on Model B, one estimated logit is: −0.20 [the constant term] + 0.84 [if the respondent is unemployed] + 1.30 [if the respondent is a council tenant] + (−0.02 *−26) [the differential for a 20-year-old] + 1.43 [the differential for living in Blaenau Gwent]. This sums to + 3.89 for an unemployed, 20-year-old council tenant living in Blaenau Gwent. The transformed percentage is obtained as [exp(L ij)]/[1.0 + exp(L ij)], which is [exp3.89]/[1.0 + exp3.89], which is 99 per cent.
44 On the latter point, see also Russell, A. T., Johnston, R. J. and Pattie, C. J., ‘Thatcher's Children: Exploring the Links between Age and Political Attitudes’, Political Studies (forthcoming).Google Scholar
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47 Dulwich has a zero logit. This does not mean that it is an extremely marginal seat but that its voters do not differ from the countrywide average pattern in their relative support for Conservative and Labour.
48 These percentages are computed as illustrated in fn. 42.
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52 Software crashes were experienced when the class variables and the tenure categories were allowed to be random at the constituency level. This is caused by insufficient data to estimate the covariances in the random part, as this requires that each type of class or category be present in each constituency; with only around nine respondents in each seat, this was not always the case. It is possible to estimate the level-2 variances while constraining the covariances to zero, but this is not a recommended procedure when the variables that are being allowed to vary at the higher level form a dummy variable set: see Longford, , Manual for VARCL.Google Scholar One other model, in which the effects for unemployment were allowed to vary between constituencies, did successfully converge, but the associated variance did not approach significance.
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