Candidates in the 2019 general election appear to have been subject to considerably more online abuse than even two years ago, with about one in six messages directed at them deemed to be insulting or abusive, according to a study.

The research involved analysis of 139,564 tweets sent on 11 November, which either replied to or otherwise mentioned any of the 2,503 candidates who are users of Twitter.

PoliMonitor, a tech-based political company, carried out the study with a grant from the Joseph Rowntree Reform Trust and found that 23,039, or 16.5% of the total, were abusive.

A study during the 2017 election carried out by the University of Sheffield found about 4% of tweets mentioning candidates were abusive. However, the methodology was different, meaning the results cannot be directly compared.

In 2019, the abuse seemed notably concentrated, with 515 of the 2,503 candidates not receiving any at all, and 150 being the target for 96% of abuse.

The most-insulted individual was Boris Johnson, followed by Jeremy Corbyn and Jo Swinson. Diane Abbott, the shadow home secretary, who is often the focus of mockery by the Conservatives, received 885 abusive or insulting tweets over the day.

Female candidates received slightly more abusive tweets than men – 17.3% of all messages against 16.2% – and those aimed at women were often focused on their appearance, as well as their gender.

The report will raise concerns about the level of threat and abuse faced by politicians, in the wake of the decision by a series of MPs, many of them female, to cite online insults and harassment as a reason not to stand again.

Before the election, women’s groups expressed alarm after MPs including the culture secretary, Nicky Morgan, and Heidi Allen, the former Conservative MP who defected to the Liberal Democrats via Change UK, said they were stepping down and mentioned attacks and intimidation as one factor.

At the time, Sam Smethers, the chief executive of the Fawcett Society, said it appeared that “our toxic politics is driving good women MPs away”, noting that politics remained “a hostile environment for women”.

Parliamentary authorities have announced that newly elected MPs will, for the first time, be given an induction session on security and wellbeing, covering areas such as online security, staying safe within and outside parliament, and general wellbeing services.

A spokesman said: “The safety and security of MPs and their staff both on the parliamentary estate and elsewhere is an absolute priority.

“We work closely with local police forces, who are responsible for the security of MPs and their staff away from the parliamentary estate, to ensure MPs are kept safe and are able to perform their duties.”

Chiara Capraro, Amnesty’s programme manager for women’s rights, said: “Our research has shown the shocking levels of abuse on Twitter that is hurled against women in politics – including death and rape threats – and the chilling effect this can have on their lives.

“We shouldn’t be seeing women politicians feel the need to self-censor, leave social media or even quit politics altogether because of the dangerous abuse they receive.”