Sunday, June 7, 2015

Charting the collapse of the Palmer United Party

There was a time when the Palmer United Party (PUP) looked like a force to be reckoned with. It commanded 6.5 per cent of the primary vote, a seat in the House of Representatives, and Senate seats for Queensland, Tasmania and Western Australia. But since then, the PUP share of the primary vote has fallen dramatically.

For those who are interested in these things, I aggregated the Palmer primary vote polls using a Beta-walk model. The Beta-walk model follows.

model {

    #### -- observational model
    for(poll in 1:NUMPOLLS) { # for each poll result - rows
        adjusted_poll[poll] <- walk[pollDay[poll]] + houseEffect[house[poll]]
        palmerVotes[poll] ~ dbin(adjusted_poll[poll], n[poll])

    #### -- temporal model (a daily walk where this today is much like yesterday)
    tightness <- 50000 # tightness of fit parameter
    for(day in 2:PERIOD) { # rows
        binomial[day] <- walk[day-1] * tightness
        walk[day] ~ dbeta(binomial[day], tightness - binomial[day])

    ## -- weakly informative priors for first day in the temporal model
    alpha ~ dunif(1, 1500)
    walk[1] ~ dbeta(alpha, 10000-alpha)

    #### -- sum-to-zero constraints on house effects
    for(house in 2:HOUSECOUNT) { # for each house ...
        houseEffect[house] ~ dnorm(0, pow(0.1, -2))
    houseEffect[1] <- -sum(houseEffect[2:HOUSECOUNT])

I did not include Palmer United in my primary vote models because Newspoll does not publish a primary vote estimate for Palmer United. Newspoll includes Palmer United in its other parties count.

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