If I recall, 40% is the domestic violence coming from either member in the household. Not just the police officer.
You recall incorrectly. The 40% does in fact refer specifically to the officers. You are correct about the definition of violence being vague though, which is why I included the second quotation in my TLDR. The rate of physical violence was around 10% according to the spouses of the officers, with the other 30% apparently consisting of verbal abuse and threatening but non-physical behavior.
The actual document transcribing the hearing I quoted from is here: https://files.eric.ed.gov/fulltext/ED338997.pdf For convenience I will be referencing the page numbers in the pdf file and at the bottoms of pages, not the original numbers at the tops of pages (which are five behind). Dr. Leanor Boulin Johnson's part of the hearing begins near the end of page 37, and she addresses congress for two and half pages. Then in pages 41-53 her prepared statement is included.
In her oral statement, she said the following (page 39) :
We found that 10 percent of the spouses said they were physically abused by their mates at least once during the last six months prior to our survey. Another 10 percent said that their children were physically abused by their mate in the same last six months.
How these figures compare to the national average is unclear. However, regardless of national data, it is disturbing to note that 40 percent of the officers stated that in the last six months prior to the survey they had gotten out of control and behaved violently against their spouse and children.
The written report says the same thing, with a bit of elaboration (page 47):
Ten percent of the spouses reported being physically abused by their mates at least once; the same percentage claim that their children were physically abused. The officers were asked a less direct question, that is, if they had ever gotten out of control and behaved violently against their spouse and children in the last six months. We did not define the type of violence. Thus, violence could have been interpreted as verbal or physical threats or actual physical abuse.
Approximately, 40 percent said that in the last six months prior to the survey they had behaved violently towards their spouse or children. Given that 20-30 percent of the spouses claimed that their mate frequently became verbally abusive towards them or their children, I suspect that a significant number of police officers defined violent as both verbal and physical abuse. Further analyses showed that years on the force were not associated with violent spouse behavior. However, among male officers violence towards children jumped 12 percent after the first three years (i.e., 28 percent in the first three years and 40 percent in years four to seven); another nine percent leap occurred after eight years of service. Although the relationship between tenure and violence was not statistically significant for females, four to seven years showed the highest frequency of violence toward their spouses and children. However, unlike the males the frequency of reported violence subsided after the seventh year.