The researchers of the study came from the University of Buffalo, Rutgers, and Yale University. What they did is they signed up 634 couples within a period of three years (1996-1999) as they were seeking to get a license for marriage in the state of New York. After interviewing the couples, the researchers maintained their contact with them for nine straight years by sending them mail-in surveys. The surveys dealt with finding out the relationship between marijuana use and intimate partner violence (IPV).

IPV is defined by the study as acts that show physical aggression. These would include choking, beating, hitting, and slapping. It was determined in the study by yearly asking the couples if they committed or became a victim of violence. The responses for every year were recorded and compared against each other.

On the conclusion of its first year, the study noted that husbands who had committed domestically violent acts covered 37.1 percent.

Apart from measuring the acts of violence as a variable in the study, it also measured the use of marijuana among the participants. Couples would then be asked on their frequency of using marijuana in the last year. They were also asked about using other drugs and drinking alcohol since the latter and marijuana are usually used together.

In the past, studying the relationship between using marijuana and domestic violence is based largely on cross-sectional data which means that the data are gathered from one point at a time. The achieved results were mixed in such a way that some studies had successfully linked marijuana use and domestic violence while some did not show any relation.

The latest study so far is just one of the conducted few that use collected data over several decades. It examines the question and places it on solid methodological ground as it compares the latest result with what is achieved in previous work.

Researchers were surprised to find out that the results were contrary to what they hypothesized. Since alcohol and other kinds of substances are commonly perceived to increase cases of domestic violence, researchers hypothesized that using marijuana will bring the same violent type of behavior.

"More frequent marijuana use generally predicted less frequent IPV for both men and women over the first nine years of marriage," researchers say. Moreover, couples that both use marijuana and in frequent times, compared to those couples where one spouse use it more often than the other, have the lowest tendency of committing or experiencing partner-directed violence.

The study is authored by Philip H. Smith, PhD, and was published in the online edition of Psychology of Addictive Behaviors in August.

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