Then-Labour leader Andrew Little also opposed the change.
The longitudinal New Zealand Attitudes and Values Study (NZAVS) happened to include questions measuring voters' attitudes about changing the flag in 2013, before the referendum was introduced, and again in 2016, after it had been introduced.
Satherley and colleagues capitalised on these data, examining participants' support for changing the flag ("yes," "no," or "unsure") and the degree to which participants in the study also supported or opposed the National and Labour parties.
As the researchers hypothesised, the data showed that participants tended to shift their opinions to align with those of their preferred political party.
Overall, 30.5 per cent of National voters and 27.5 per cent of Labour voters moved away from the position they originally reported in 2013 to become closer to, or consistent with, the position endorsed by their party leader.
In other words, the researchers found that support for either National or Labour predicted whether individual voters remained stable in their views or changed over time.
Relative to remaining opposed to changing the existing flag design, strong National supporters were more than three times as likely to shift their opinion in favour of a flag change compared with those who expressed low support for National.
At the same time, staunch Labour supporters who originally backed the change were more likely to shift toward opposing the change, compared with participants who expressed low support for Labour.
And strong party supporters whose opinions were already in line with the party position were less likely to shift their attitudes over time compared with participants who expressed low levels of party support.
"Taken together, these findings suggest that heated debate over important, albeit seemingly non-partisan, issues can quickly become polarised along partisan lines and sway public opinion," Satherley explained.
"When considering political issues, members of the public should therefore be aware of this potential influence, and carefully consider whether politicians' views and arguments truly align with their own opinions."
The researchers said the findings raised some important questions for future research, such as what motivated party supporters to switch their votes, and whether they did so to align themselves with their party leaders, or just to combat the opposing party.
They said future work should also explore other factors likely to make a difference in the strength of partisan effects, such as political awareness, the perceived importance of an issue, and the degree of polarisation on an issue.
"In the future, we would like to continue examining other outcomes that partisan cues impact and then identify the factors that reduce such partisan effects in real-world settings."
The study has been published in the international journal Psychological Science.
