Have you read the sources? What aspects of the research led you to conclude they are the most reliable, particularly in light of my concerns about the survey you previously posted?
Well for one thing, this is a non-profit organisation dedicated to ending domestic abuse for all types of people. It's not specifically focused on LGBT or trans people, which isn't necessarily indicative of a bias but could be the cause of one.
I've read R.L Stotzer's work, the Department of Justice I imagine is reliable. I think all their sources are peer-reviewed scholarly articles or directly from the Department of Justice, except Trans Student Educational Resources. However that is only used for the definitions given at the beginning so doesn't impact the actual stats.
What did you find most reliable about this study?
The survey was funded by the Scottish Government; it isn't an icky college website with a poor set-up, for one thing. It's a high-profile and well-reputed information resource concerning trans people.
The fact that they had a page before on methodology where they brought up possible shortcomings is a huge indicator of reliability to me. It is unlikely to have reached the whole trans population. It may not, for example, have reached transitioned people who no longer see themselves as being ‘trans’ or those who are isolated by other circumstances from transgender support networks. It usually suggests that it's been well thought out and they have considered the reliability of the survey before publishing.
They had a pretty good age distribution, a reasonable balance of responses from MTF and FTM. There was also a good variant in sexuality. The majority were well educated which (makes me sound dreadfully snobby I know) might make them more reliable in a survey.
The vast majority of them had had a fair amount of partners.