Taiwanese Public Opinion on the Chinese and US Military Presence in the Taiwan Strait

Abstract Since 2016, China has been conducting military flybys around Taiwan, while the US has approved arms sales to Taiwan on several occasions and sent warplanes and battleships through the Taiwan Strait. How does Taiwanese public opinion respond to the Chinese and US military presence in the Strait? Is the public likely to become less supportive of de jure independence for Taiwan on account of China's military deterrence or more supportive owing to a perceived likelihood of US military assistance? In this report, we provide answers to these questions based on evidence from a survey experiment conducted in Taiwan in October–November 2020. We find that Taiwanese are less sensitive to the Chinese military presence in the Taiwan Strait but have become more supportive of de jure independence after seeing the US aircraft in the area. Our findings contribute to studies of cross-Strait relations and US foreign policy on the Taiwan Strait.

minister, Chiu Kuo-cheng 邱國正, warned that tension between Taiwan and China was worse than at any time during his more than 40-year military career and that China would be capable of invading Taiwan by 2025. 3 During the visit to Taiwan in early August 2022 of US House of Representatives speaker Nancy Pelosi, China announced it would conduct military exercises near Taiwan and 22 Chinese military aircraft flew into the ADIZ and crossed the median line of the Taiwan Strait.
Amid this intensification of hostility between Taiwan and China, the US is playing a crucial role in maintaining stability in the Taiwan Strait.Although the US has no formal security commitment to Taiwan, it approved several deliveries of arms sales to Taiwan during the Trump administration.It also sent military aircraft and warships to transit through the Taiwan Strait in 2021.John Kirby, spokesman for the US Defense Department, claimed that Chinese military activities around the Taiwan Strait are "destabilizing and only increase the risk of miscalculation." 4He noted that the US "support for and defense relationship with Taiwan remains aligned against the current threat posed by the People's Republic of China." 5 The existing literature includes some extensive investigations of how the Chinese threat and Washington's informal security commitment to Taiwan contribute to the dynamic peace across the Taiwan Strait.Yet there are few studies that examine how military action by the US and China in the Taiwan Strait shapes Taiwanese public opinion, specifically how such action affects Taiwanese citizens' perceptions concerning China's resolve to attack Taiwan and the US commitment to assist Taiwan's defence.For example, would Taiwanese citizens become less (or more) supportive of de jure independence as a result of China's aggressive behaviour or the prospect of US military assistance?In this report, we attempt to answer these questions by analysing data from an online survey experiment conducted in Taiwan in October 2020.
This report proceeds as follows.In the next section, we discuss the US policy of strategic ambiguity and its implications.Then, we introduce four hypotheses on how the US and Chinese military presence in the Taiwan Strait affects Taiwanese public opinion.In the empirical section, we present the design of our survey experiment and the results.We draw our conclusions in the final section.

The US Policy of Strategic Ambiguity towards Taiwan
Although the US has had no formal mutual defence treaty with Taiwan since the termination of the Mutual Defence Treaty between the United States of America and the Republic of China (Taiwan's official name) in 1979, the Taiwan Relations Act (TRA) commits the US to maintaining Taiwan's ability to defend itself.Under the TRA, the US not only continues to sell defensive weapons to Taipei but also engages in bilateral military exchanges and activities with Taiwan.The most notable example of this commitment is the US deployment of two aircraft carrier battle groups in the Taiwan Strait in response to China's missile tests in waters surrounding Taiwan in 1996.With more and more Chinese military aircraft appearing in the Taiwan Strait since the Democratic Progressive Party (DPP) won the presidency in 2016, the US has offered other forms of military assistance to Taiwan, including approving several arms sales and sending warplanes and warships to transit through the Taiwan Strait.
While the US, under the terms of the TRA, is helping Taiwan to strengthen its military capability, it adopts an ambiguous stance concerning its security commitment to Taiwan.Specifically, the US neither commits to protecting Taiwan from a Chinese attack nor does it say it will not do so. 6This policy is described as one of "strategic ambiguity."As the US has never expressly stated its position or indicated what action it might take in the event of a cross-Strait military conflict, China lives under the shadow of possible US intervention if it unilaterally attacks Taiwan.Meanwhile, Taiwan needs to take into account the possibility that the US would refrain from offering military assistance if a declaration of de jure independence by Taipei provoked a Chinese attack.Accordingly, the US policy of strategic ambiguity has led to "dual deterrence" in the Taiwan Strait and kept peace in the Asia-Pacific region. 7lthough some policy experts suggest that the US, faced with China's growing military capability, should renounce strategic ambiguity and make a clear commitment to defend Taiwan against any military attack from China,8 other scholars warn that possible entrapment in a cross-Strait conflict would be too costly for Washington.9Bonnie Glaser, for example, argues that if the US extends "an unqualified security commitment to Taiwan … China could respond by mounting an attack," because an unconditional commitment "could embolden pro-independence constituencies in Taiwan to promote their cause."10In other words, the US must maintain its strategic ambiguity to discourage a pro-independence Taiwanese government from making a unilateral declaration of de jure independence.
As strategic ambiguity may be contributing to cross-Strait stability, it is indeed a difficult task for the US to manage the magnitude of its military assistance to Taiwan.Thomas Christensen argues that the US and Taiwan must enhance their military security to counter China's military buildup.11Yet while US assistance to Taiwan strengthens the island's military capability, it may also encourage Taiwanese to seek de jure independence, thereby reinforcing China's apprehension.To address this dilemma, Christensen highlights the importance of US "reassurance" to both Taiwan and China.In particular, the US should reassure China that US-Taiwan military cooperation will not lead to US support for de jure Taiwan independence.Washington should also offer Taiwan "a clear but conditional" security commitment that emphasizes the maintenance of Taiwan's democracy but not its pursuit of de jure independence.
These scholars focus on how political leaders and decision makers perceive and respond to the US policy of strategic ambiguity; the perceptions and reactions of ordinary citizens are often overlooked.We should also be asking how Taiwanese citizens perceive the Chinese and US military presence in the Taiwan Strait and whether Chinese military actions are succeeding in deterring Taiwanese from supporting de jure independence.Another question of interest is whether US military assistance to Taiwan makes the Taiwanese more confident in pursuing de jure independence, as it offers the possibility that the US will come to Taiwan's defence.To the best of our knowledge, previous studies focus on how the Chinese military threat and US military assistance would conditionally affect Taiwanese support for independence.12They make a key assumption that the Taiwanese would respond to US and Chinese military (in)action and make their choices concerning Taiwan's future accordingly.This assumption, however, lacks concrete empirical support in the existing literature.There is no direct empirical evidence to show that military activity by the US or China would either deter Taiwanese citizens from pursuing de jure independence or encourage them to do so.
This report aims to fill this gap by means of an experimental survey of Taiwanese citizens.We propose the following four hypotheses concerning whether the presence of the Chinese and US military in the Taiwan Strait shapes Taiwanese citizens' perceptions of China's willingness to attack Taiwan and the United States' resolve to defend Taiwan, and how these perceptions would affect their support for Taiwan's de jure independence:

Research Design Sample
To test our hypotheses, we commissioned an online survey experiment in Taiwan between 29 October and 10 November 2020.Our survey offers a good test of whether the Chinese and US military presence in the Taiwan Strait has influenced Taiwanese public opinion, particularly as its timing meant that respondents were not affected by the escalation of tensions between China and the US that occurred after the inauguration of President Joe Biden in January 2021.For instance, in the first year of Biden's presidency, the US imposed several rounds of economic sanctions on Chinese companies and Hong Kong-based Chinese officials in response to China's violation of human rights in Xinjiang and Hong Kong.China then promulgated its Anti-Foreign Sanctions Law to counter these sanctions.Our survey predated these escalations.
After conducting power analysis, we asked a marketing company, i-Vision Marketing Consultant, to recruit 600 respondents through quota sampling.Each respondent who completed the survey was rewarded with a voucher worth NT$50 (about US$1.60).The sample and population characteristics are reported in Table A.1 in the Appendix, which shows that our sample is not representative of the population because the respondents are more educated and younger than the general public.Nevertheless, our primary focus in this report is not the absolute levels of respondents' political attitudes.Instead, we investigate whether their attitudes would be different after they received treatment conditions (discussed below).In other words, in this experimental study we estimate the treatment effect via calculating the mean differences between the control and treatment groups.The key to identifying the treatment effect is to assign respondents randomly to different experimental groups.A successful random assignment process enables researchers to attribute the group differences to the treatment conditions.Table S.1 in the online supplementary materials displays the balance table after the randomization process and suggests that random assignment was successful as there is no significant difference between the features of respondents across the experimental groups.

Experimental primes
Our experimental survey comprises three parts.Part one consists of questions on respondents' demographic traits, including age, gender, area of residence, education and party identification.We also asked respondents to evaluate the security threat from China and the state of Taiwan's relationship with China and the US.Part two includes our experimental primes on the Chinese and US military presence in the Taiwan Strait.Utilizing the increasing public awareness of the presence of Chinese and US military aircraft over the Taiwan Strait, we asked all the respondents to view a map of Taiwan's ADIZ (see Figure 1) and read the following short description of an ADIZ: An air defence identification zone (ADIZ) is airspace over land or water in which the identification, location and control of aircraft is performed in the interest of national security.The concept of an ADIZ is not defined in any international treaty and an ADIZ may extend beyond a country's territory.If a military or civil aircraft that enters a country's ADIZ threatens that country's national security, that country may expel the intruding aircraft.The map [Figure 1] shows the ADIZ of Taiwan, including the mid-line of the Taiwan Strait and the waters surrounding Taiwan.
After they had read the above description and viewed the map of Taiwan's ADIZ, we randomly assigned respondents to one of three experimental groups: the US group, the Chinese group and the control group.Respondents assigned to the US group saw a map on their screens showing US aircraft in or around Taiwan's ADIZ (Figure 2a).Similarly, respondents in the Chinese group saw a map showing Chinese aircraft in or around Taiwan's ADIZ (Figure 2b).Both groups of respondents were told that the maps showing the military aircraft were based on recent occurrences in the region.To make sure that our manipulation was successful, on the next page, we asked respondents in both groups to identify the nationality of the military aircraft depicted on the maps.About 2.3 per cent of respondents failed to pass the manipulation check, and we excluded them from the analysis.Finally, the control group did not see any maps showing foreign military aircraft in and around Taiwan's ADIZ.
After reading this material, all three groups of respondents were asked to answer the third part of the questionnaire, which included the three dependent variables of this study.We discuss these variables in detail below.

Dependent variables
We are particularly interested in three outcomes after our respondents receive the treatment conditions.First, China has stipulated in its Anti-Secession Law that it will use military force against Taiwan should Taiwan declare de jure independence, so we are interested in whether seeing evidence of China's military aircraft in the vicinity of Taiwan would increase our respondents' belief that China will attack Taiwan if Taiwan declares de jure independence.Thus, we asked respondents the following question: "If Taiwan declares independence, no matter what the circumstances, do you think that China will attack Taiwan?" 13 We measured respondents' evaluation of the likelihood of a Chinese attack on a 6-point Likert scale (i.e.very unlikely, unlikely, somewhat unlikely, somewhat likely, likely, and very likely).
Given Washington's policy of strategic ambiguity towards relations between the two sides of the Taiwan Strait, our second quantity of interest is respondents' belief in the willingness of the US to offer military assistance in the event of a Chinese attack after seeing evidence of US military aircraft in and around Taiwan's ADIZ.Therefore, we asked respondents the following question: "If a Taiwanese declaration of independence will lead to an attack by mainland China, do you think the United States will deploy troops to help Taiwan?" 14 We used the same 6-point Likert scale to measure respondents' perception of US willingness to help Taiwan.
Third, we investigated whether the presence of Chinese and US military aircraft in and around Taiwan's ADIZ would affect respondents' support for de jure Taiwan independence.Previous studies argue that China's threat of using force against Taiwan has deterred some Taiwanese citizens from supporting Taiwan independence, whereas US assistance to Taiwan against China would increase their support for it. 15Yet it is unclear whether the actual military presence of two major powers would affect Taiwanese citizens' support for Taiwan independence.To explore this question, we asked the following standard question on the issue of unification/independence: "Concerning the relationship between Taiwan and mainland China, which of the following six positions do you agree with?(1) Immediate unification; (2) immediate independence; (3) maintain the status quo and move towards unification in the future; (4) maintain the status quo and move towards independence in the future; (5) maintain the status quo and decide either unification or independence in the future; (6) maintain the status quo forever."Since we are particularly interested in investigating whether Chinese and US military presence in the Taiwan Strait would affect Taiwanese support for Taiwan's de jure independence, we created a dummy variable to indicate whether respondents are supportive of Taiwan independence, including immediate independence and maintaining the status quo and moving towards independence in the future. 16efore presenting the empirical results of our study, we would like to note that our research design can only identify the short-term effects of Chinese and US military presence on the dependent variables, including the perceived likelihood of Chinese and US military actions and individual support for Taiwan independence.First, we primed our respondents with recent episodes of military flybys by both the US and China, so we are unable to make an inference about the long-term effects of Chinese and US military presence.Second, our respondents were only contacted once and the treatment groups received only one treatment condition (discussed below), so the effect we identify in this study may be transient and temporary.Nevertheless, if we are able to find that there are short-term effects of a military presence on individual perceptions and attitudes, then we can further explore conditions under which these effects can endure or disappear.

Empirical Results
As we were conducting a between-subjects experiment, we used t-tests to test our hypotheses and visualized the results in the following figures.First, we tested whether seeing Chinese or US aircraft in Taiwan's ADIZ had affected respondents' evaluation of the likelihood of China attacking Taiwan 13 Niou 2004.14 Ibid.15 Hsieh and Niou 2005; Niou 2004.16 We conducted additional analyses to check the robustness of our findings.First, we created a 5-point ordinal variable to measure respondents' support for Taiwan independence with the two choices of the status quo as the midpoint (i.e. 3).Then, we estimated OLS models with this variable as the dependent variable.Second, we used the status quo as the baseline category and estimated a multinomial logit model.(Hypothesis 1) or the US defending Taiwan (Hypothesis 2).With dashed lines to indicate statistically insignificant differences between two groups (i.e.p > 0.1, two-tailed test), Figure 3 shows that there is insignificant difference in respondents' perception of the likelihood of a Chinese attack, although those respondents who viewed evidence of US or Chinese aircraft tend to perceive that there is a higher likelihood of an attack than those who did not view any of the treatment maps.Nevertheless, it should be noted that the average perceived likelihood in the control group is 4.503 on the 1-6 scale.In other words, our respondents' perception of the likelihood of a Chinese attack is already high owing to the intensification of China's threats against Taiwan since 2016, so it may be unsurprising that receiving additional information concerning the Chinese military presence does not significantly change their evaluation.
Similarly, Figure 4 shows the results of the perceived likelihood of US military assistance to Taiwan in the event of a Chinese attack across different experimental groups.We use dashed (solid) lines to indicate statistically insignificant (significant) differences between two groups, with a p-value of 0.1 as the threshold of statistical significance.Respondents in the US group have a higher evaluation of the likelihood of the US sending troops to Taiwan to defend against a Chinese attack than their counterparts in the control group (difference = 0.32, p = 0.017).While the substantive effect of this treatment is small (i.e.0.32 on the 1-6 scale), the difference between the control group and the US treatment group is statistically significant at the p < 0.05 level.This result confirms Hypothesis 2.
In addition, Figure 4 shows that, surprisingly, respondents in the China group have a higher evaluation of the likelihood of US military assistance than those in the control group (difference = 0.25, p = 0.046).Although this difference is not substantial, it needs further investigation for this unexpected result.Here, we propose one possible mechanism.Specifically, the results in Figure 3 suggest that our respondents already perceive a high risk of a Chinese attack (4.50 on the 1-6 scale), and their perceived risk of a Chinese military attack would not significantly change after seeing a greater Chinese military presence around the Taiwan Strait.Yet our respondents may already think that the US is likely to come to Taiwan's aid in the event of a military attack from China, so seeing evidence of Chinese military aircraft in or around Taiwan's ADIZ would enhance their perception of the likelihood of US military assistance to Taiwan. 17We encourage future studies to explore how Taiwanese citizens' psychological sentiments about the US would affect their expectations of US policy towards Taiwan.
Results in Figure 5 support our third hypothesis on the relationship between evidence of US military assistance and support for Taiwan independence.In particular, support for Taiwan independence is significantly higher in the US group than in either the control or China groups, whereas the difference in support is statistically insignificant between the control and China groups.Specifically, support for independence is, on average, 9.69 per cent higher among the respondents who viewed the map showing US military aircraft in or around Taiwan's ADIZ than it is among respondents who saw neither US nor Chinese military aircraft in or around the ADIZ.Meanwhile, seeing evidence of Chinese aircraft in or around Taiwan's ADIZ did not reduce respondents' support for Taiwan independence, as the difference in support between the control and China groups is statistically insignificant (p = 0.309).
In addition to visualizing the results of t-tests between experimental groups, we estimated regression models in which we included dummy variables for our experimental groups and variables that are correlated with respondents' political attitudes.We controlled for respondents' age, gender, level of education and partisanship.Based on respondents' evaluations of the level of peace between Taiwan and the US and the level of peace between Taiwan and China, we created two variables, one on respondents' evaluations of Taiwan's affinity with China and the other on Taiwan's affinity with the US, because these evaluations are likely to be correlated with their perceived likelihood of a Chinese attack on Taiwan and US military assistance to Taiwan, respectively.Owing to space constraints, we report the operationalization of these variables in Table S.2 in the supplementary materials.
Our estimation results, as shown in Table 1, suggest that our key findings remain unchanged. 18The US treatment increased respondents' perceived likelihood of the US assisting in the defence of Taiwan by 0.316 points on a 1-6 scale.It also increased their probability of supporting Taiwan's de jure independence by 8.44 per cent (Model 3).In addition, the variables of perceived affinity are correlated with the perceived likelihood of a Chinese attack on Taiwan and US military assistance to Taiwan.Respondents perceiving a high level of Taiwan-China affinity perceive a lower risk of a Chinese attack, whereas those perceiving a high level of Taiwan-US affinity perceive a greater likelihood of the US defending Taiwan against China. 19he results of Models 2 and 3 in Table 1 further suggest that respondents' perceived likelihood of the US defence of Taiwan would mediate the relationship between the treatment condition and support for Taiwan independence.Thus, we estimate a causal mediation model suggested by Kosuke Imai and colleagues and report the results in Table 2. 20 We find that respondents' perceived likelihood of US assistance increases under the US aircraft condition (Model 1a), and such a perception increases their support for Taiwan's de jure independence (Model 1b).In particular, the perceived likelihood of US military assistance mediates 13.09 per cent of the total effects of the US aircraft treatment. 21These results reconfirm our findings in Table 1.18 Table S.5 reports the standardized coefficients.19 Although the questions on affinity were asked before the experimental primes in our survey, we do not find any empirical evidence to indicate that they played a moderating role between the experimental conditions and the outcomes.We report these results in Our findings contribute important empirical evidence to the ongoing debates over the US policy of strategic ambiguity with regard to cross-Strait relations.While Taiwanese citizens are accustomed to the military threat from China, our study shows that they are responsive to US policies and adjust their support for Taiwan independence accordingly.Therefore, it is possible that Taiwan, emboldened by US military assistance, may act in such a way as to provoke a Chinese attack (i.e. by pursuing de jure independence).Yet that does not mean that the US must give up its policy of strategic ambiguity.Instead, our study shows that strategic ambiguity could be an effective tool for maintaining stability in the Taiwan Strait.This is because by adjusting the level of ambiguity, particularly with regard to military assistance, Washington can discourage Taiwan from taking any reckless action.
There are three directions for future study.First, it would be useful to investigate the underlying psychological mechanisms that cause evidence of a Chinese or US military presence to influence Taiwanese public opinion.Specifically, Taiwanese citizens may be experiencing fatigue regarding China's military threat yet be alert to the ambiguous commitment of the US to Taiwan's national security.As the US is the key security provider in East Asia, any US military actions in the Taiwan Strait would shape Taiwanese citizens' beliefs in the US commitment to Taiwan's security and their support for Taiwan independence.Second, this study identifies short-term effects of two major powers' military presence on respondents' perceptions and political attitudes.Future research may conduct panel studies to investigate whether and how the effects would transform into longterm ones and endure over time.It can further help us to gain a better understanding of whether US military assistance to Taiwan's national security would embolden Taiwanese support for independence.Third, one can explore how Chinese and US citizens perceive the presence of each other's military in the Taiwan Strait and how their perceptions are related to their attitudes towards cross-Strait relations.With a more nuanced research design and by using multiple surveys conducted at different times and in different countries, we could gain a more comprehensive understanding of the dynamics of cross-Strait relations.

H1:
The Chinese military presence in the Taiwan Strait increases the perceived likelihood among Taiwanese citizens of a Chinese attack on Taiwan.H2: The US military presence in the Taiwan Strait increases the perceived likelihood among Taiwanese citizens of the US coming to Taiwan's defence.H3: The Chinese military presence in the Taiwan Strait reduces Taiwanese citizens' support for de jure independence.H4: The US military presence in the Taiwan Strait increases Taiwanese citizens' support for de jure independence.

Figure 1 :
Figure 1: The ADIZ of Taiwan

Figure 3 :
Figure 3: Perceived Likelihood of a Chinese Military Attack on Taiwan Note: In this and the following figures, a dashed horizontal line indicates the difference is statistically insignificant between two groups (p > 0.1).

Figure 4 :
Figure 4: Perceived Likelihood of US Military Assistance to Taiwan

Figure 5 :
Figure 5: Support for Taiwan Independence, by Experimental Group Note: A dashed horizontal line indicates the difference is statistically insignificant between two groups (p > 0.1), whereas a solid horizontal line indicates a statistically significant difference (p < 0.1).
Table S.6.20 Imai et al. 2011.21 We report the results of sensitivity analysis in Figure S.2.