I've read this book more than once due to coursework related to criminology and psychology. While I do think Zimbardo conveyed his findings with (almost excessive) transparency, this book having been written well after the experiment, it’s safe to say that by modern standards, and perhaps to some extent standards of the day, his work was obviously unethical.

Aside from offering money to participants, there wasn’t a lot of direct value to them in the research, although many of the subjects (24) perceived themselves as working to benefit science, and the research was framed as such. Zimbardo conceded in this book that the work was not very generalizable since it relied entirely on a meager convenience sample (mostly Stanford students, though as I recall, he said that not all of the participants were students). Furthermore, the quality of the simulation of a prison environment (they worked in a makeshift prison environment constructed in a Stanford University basement) was questionable.

In any case, the study's lack of ethical rigor is clear. Participants were regularly subjected to intentional distress by participant guards in authority over them (a couple days into the experiment, some of the volunteer prisoners were planning escapes and riots). Participants were regularly locked in a “hole” for extended periods for defiance of the guards (in some cases, for refusing to eat). Participant prisoners were lied to about being able to leave the experiment, both by their fellow prisoners and by Zimbardo himself (more so through a lie of omission in the case of the latter).

Dr. Zimbardo established a relationship of trust with the volunteers, both prisoners and guards, to some extent. Most trusted him as a scientific researcher primarily and in his roleplay as prison superintendent, and he effectively abused that trust in some cases by, as noted, doing things such as letting prisoners believe they couldn’t leave. (There was, if I remember rightly, at least one participant who believed that Dr. Zimbardo was a government operative trying to find ways to break the will of anti-war protesters.)

While most of those in guard roles did not viciously abuse their authority, participant prisoners were regularly degraded by their peer guards. They were made to stand for long periods and recite monotonous phrases and perform pointless exercises; they were forced to engage in sexually revealing and degrading behavior, sometimes with one another. They were regularly subjected to disruptions of their sleep by being woken up at odd hours and forced to do things such as engage in physically-exhausting activity like jumping jacks.

I think Dr. Zimbardo’s research would’ve had the same ethical considerations as work done with Genie Wiley. Though, in her case, I think the research “on” or with her was conducted more ethically than the research carried out by Dr. Zimbardo (and the findings were probably of more value to psychology). I’m not sure Dr. Zimbardo’s study idea could be carried out ethically.

Overall, the book is interesting because it offers an insight into a famous and classical experiment, similar to the Milgram Experiment (also unethical by modern standards). The studies are interesting because they are unique to their time and would not occur today. Their value to science, either criminological or psychological, lies more in their existence as measures of ethical evolution throughout history than their findings themselves, which are largely worthless.