Why does SAMHSA caution against comparing many 2015 estimates with estimates from prior years?

For the 2015 NSDUH, several changes were made to the questionnaire and data collection procedures for drug use:

• The NSDUH questionnaire adopted a revised definition of prescription drug misuse.
• The prescription drug questions for pain relievers, tranquilizers, stimulants, and sedatives were redesigned to shift the focus from lifetime misuse to past-year misuse.
• Questions were added about any past year’s prescription drug use rather than just misuse.
• A separate section with methamphetamine questions was added, replacing the methamphetamine questions that were previously asked within the context of prescription stimulants.
• Substantial changes were made to questions about inhalants, hallucinogens, smokeless tobacco, and binge alcohol use.

These changes led to potential breaks in the comparability of 2015 estimates with estimates from prior years, especially for overall summary measures, such as:

• any illicit drug use
• use of illicit drugs other than marijuana
• use of hallucinogens, inhalants, and methamphetamine
• misuse of psychotherapeutics
• binge and heavy alcohol use
• smokeless tobacco
• substance use treatment
• perceptions of risk of harm associated with substance use
• perceived availability of substances.

Additionally, certain demographic items were changed as part of the partial redesign. Employment questions were moved from the computer-assisted personal interviewing section to the audio computer-assisted self-interviewing section of the questionnaire. Education questions were updated, and new questions were added on disability, English-language proficiency, sexual identity and sexual attraction, and military families.

Other topics, such as those on mental health, did not undergo major changes and, therefore, are considered comparable.

More details on these changes are available from the 2014 and 2015 Redesign Changes report.