Exploring Trends in Substance Use through Data Visualization
The National Survey on Drug Use and Health (NSDUH) is an annual survey conducted by the Substance Abuse and Mental Health Services Administration (SAMHSA). This survey employs rigorous statistical sampling to capture current and former substance use statistics of nearly 60,000 civilian, non-institutionalized US citizens over the age of 12.
It is a veritable treasure trove of information, surveying respondents on their experiences with a wide battery of legal and illicit substances. The survey also includes many other measures gauging aspects of each individual’s personal life, including their self-reported physical and mental health, social environment, demographics, education, employment, household composition, health insurance status, and income. While this brief summary grossly simplifies the richness of the available data, as the final 2015 NSDUH data set includes some 2,666 separate variables, it hopefully gives you a broad understanding of the sort of information captured by the survey.
Recently, I took it upon myself to explore the 2015 NSDUH data set, in order to examine some of the underlying statistics about substance use, abuse, and treatment in America today.
In a future post, I’ll discuss some of the inferential modeling I did to examine factors most associated with obtaining substance abuse treatment. For today, however, I’ll examine some of the initial exploratory analysis and data visualization I did while getting a handle of the broader data set.
Lifetime Reported Use of Substances
Some of the initial questions asked of respondents relate to lifetime use of different substances — that is, has the respondent used “Substance X” ever in their lives? The gated logic of the survey is structured to provide respondents further questions about each substance if answered with a “yes,” or else move on to the next series of questions if answered with a “no.”
The various substances included in the “ever used” questions can include both discrete substances (e.g., LSD) as well as families of substances (e.g., hallucinogens). I initially examined the proportion of total respondents reporting lifetime use of various substances.
From the results, we can see that the three most used substances include alcohol (over 70%), cigarettes (over 50%), and marijuana (over 40%). Notably, over 10% of respondents also report lifetime use of hallucinogens, cocaine, pain relievers (off-prescription), and inhalants.
First Use and Most Recent Use of Substances (Respondents 50 years and Older)
In addition to lifetime use of substances, I wanted to examine when individuals typically first use substances as well as their most recent use of substances across their lifetimes. The idea behind this is predominantly wondering which substances tend to be used first, but also which substances tend to be used continually over time once started.
Because I wanted to look at the use of substances over long periods of time, I restricted this analysis to examine only those respondents who are 50 years and older. For younger individuals, first use and most recent use are likely much closer together, and so could otherwise obfuscate broader trends over a lifetime.
I used violin plots for these analyses, which essentially draw a vertical distribution plot for each substance. Wider blobs indicate a larger proportion of the total measured sample.
It’s clear from this first plot that individuals’ late teens and early 20s reflect the “experimental” phases often attributed with these ages. Interestingly, crack and ecstasy have the highest median ages of first use (as indicated by the white dots in the black interquartile bars). Considering that respondents over 50 in this sample would have been born in 1965 or earlier, perhaps the later adoption of crack and ecstasy is partly related to the timing of when these substances first became broadly available?
Examining the timing of last use, it appears that most respondents left hallucinogens and inhalants largely behind in their late teens and 20s. This perhaps implies these substances being used while going through an experimental phase, or may speak to a general difficulty in obtaining these substances once one moves into a more mature life stage.
Alcohol is clearly the most persistent substance in overall lifetime use, with the largest portion of the distribution congregating in individuals’ 50s, 60s, and 70s.
It is interesting to see the more uniform distributions of substances like crack and heroin. Perhaps this implies that use of these substances is less of a “phase”?
Substance Use over Prior 30 Period
For individuals reporting use of any given substance within the past month, I also looked at the general distributions of how frequently each substance was used in the 30 days prior to respondents completing their surveys. For example, a respondent reporting use of cigarettes in 30 out of the last 30 days implies daily use, and so on.
Some findings immediately stand out. Cigarette smokers report predominantly daily use, with cigarettes being by far the most frequently used of all substances on average.
Squatter distributions, such as that for users of hallucinogens, may imply a more “recreational” nature of certain substances, something that is used less frequently for a particular kind of experience.
Marijuana appears to have something of a bimodal distribution, with noticeable swells of use at both the frequent and infrequent sides of the distribution.
Other, “harder” drugs such as heroin and methamphetamine have thinner, more uniform distributions. Perhaps this indicates something about use based on availability? Further research may reveal more.
Substance Dependence/Abuse over Prior 12 Month Period
Finally, of all respondents reporting use of a substance within the last 12 months, how many qualified as either developing a dependence on that substance, or otherwise abusing that substance?
The NSDUH codebook defines dependence and abuse of substances based on respondents’ answers to a series of questions about each substance they have used.
Dependence was determined as a positive answer to at least three of the following:
- Spent a great deal of time over a period of a month getting, using, or getting over the effects of the substance.
- Unable to keep set limits on substance use or used more often than intended.
- Needed to use substance more than before to get desired effects or noticed that using the same amount had less effect than before.
- Unable to cut down or stop using the substance every time he or she tried or wanted to.
- Continued to use substance even though it was causing problems with emotions, nerves, mental health, or physical problems.
- Reduced or gave up participation in important activities due to substance use.
- (For select substances) experiencing withdrawal symptoms at one time that lasted for longer than a day after they cut back or stopped using
To qualify as abusing a substance, respondents needed to answer in the affirmative for one of the following, and not being determined as dependent on the substance (Note: the survey codebook indicates individuals cannot be classified as “abusing” tobacco products):
- Respondent reported having serious problems due to substance use at home, work or school.
- Respondent reported using substance regularly and then did something where substance use might have put them in physical danger.
- Respondent reported substance use causing actions that repeatedly got them in trouble with the law.
- Respondent reported having problems caused by substance use with family or friends and continued to use substance even though it was thought to be causing problems with family and friends.
Again, the following graphic displays the proportions of respondents reporting use of a substance in the last 12 months who were classified as either dependent upon or abusing the substance.
Again, some findings immediately stand out.
Over 60% of respondents using heroin in the last 12 months qualified as being dependent on or abusing the substance. In addition, nearly 50% of respondents using methamphetamine qualified as dependent or abusing, and nearly 30% of nicotine product users qualified as dependent.
Finally, approximately 18% of respondents using any illicit drug (which includes marijuana, cocaine, heroin, methamphetamine, inhalants, hallucinogens, and off-prescription psychotropics) reported dependence or abuse of at least one of these substances.
While this has been a relatively brisk look through only a sliver of the data contained within the 2015 NSDUH, I look forward to further discussing some of the deeper analysis I did in an upcoming post.
I also acknowledge that I am not an expert in the use or trends of use in substances across America. I appreciate there is a vast literature that could better frame understanding of these findings. If you happen to know of any additional resources, please feel free to share!