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Test‐retest reliability of a new assessment to detect detailed temporal patterns of polysubstance use

Abstract Objective While polysubstance use is highly prevalent among people who use drugs, the field lacks a reliable assessment that can detect detailed temporal patterns of polysubstance use. This study assessed the test‐retest reliability of the newly developed Polysubstance Use–Temporal Patterns Section (PSU‐TPS). Methods Participants who used cocaine plus alcohol and/or marijuana at least once in the past 30 days (n = 48) were interviewed at baseline and approximately 7 days later (retest) using the Substance Abuse Module and the PSU‐TPS. Reliability of PSU‐TPS measures of quantity, frequency, and duration of polysubstance use was examined using intra‐class correlation coefficients (ICCs) and kappa tests. Results Excellent reliability was observed for frequencies of concurrent polysubstance use patterns in the past 30 days (ICC range: 0.90–0.94) and quantity of alcohol use (ICC = 0.83), and fair to good reliability was observed for duration of substance use (ICC range: 0.52–0.73). Conclusion Detailed information regarding cocaine, alcohol, and marijuana polysubstance use in the past 30 days can be reliably measured with the PSU‐TPS. Data on the order and timing of polysubstance use at the hourly level will improve our understanding of the implications of sequential and simultaneous use patterns, which can help inform treatment and prevention efforts.

describes which drug was used first, which second, and so on within the same occasion (e.g., within the same 24 h), while simultaneous use indicates co-administration of two or more substances at the same time or in close temporal proximity (e.g., the use of a mixture of cocaine and heroin, or smoking marijuana while drinking alcohol) (Barrett et al., 2005;McCabe et al., 2006;Olthuis et al., 2013).
Both concurrent and simultaneous polysubstance use have been found to be highly prevalent among persons who use cocaine. A meta-analysis estimated that, among those who use cocaine, 77% used alcohol and 64% used marijuana concurrently with cocaine, while 74% used alcohol and 38% used marijuana simultaneously with cocaine (Liu et al., 2018). Measures of simultaneous cocaine polysubstance use are particularly important, as research has shown that drug combinations can impact subjective responses to cocaine (Lukas et al., 1994;McCance-Katz et al., 1998) as well as neurobiological outcomes (Meyerhoff, 2017;Meyerhoff et al., 1999;O Neil et al., 2001). Using alcohol or marijuana with cocaine can affect cocaine's metabolic profile (McCance-Katz et al., 1998;Pan & Hedaya, 2000;Reid & Bornheim, 2001), potentially enhancing its reinforcing effects (Hart et al., 2000;Jatlow et al., 1991;Raven et al., 2000). Given that these substances can interact both metabolically and neurobiologically depending on the timing of their overlapping use, collecting data on concurrent use alone is insufficient for a comprehensive understanding of the etiology and consequences of cocaine polysubstance use patterns.
Despite the importance of considering the timing and order of sequential and simultaneous polysubstance use, few studies have examined the temporal ordering of cocaine use with alcohol and/ or marijuana. Of the five studies that have investigated the order and sequencing of simultaneous cocaine and alcohol use (Barrett et al., 2006;Barrett et al., 2005;Gossop et al., 2006;Macdonald et al., 2015;Staines et al., 2001), the majority found that alcohol use generally proceeded the use of cocaine on days in which both were used, with the exception of Gossop et al. (2006), who found that a greater proportion of persons who used crack cocaine reported drinking alcohol after using crack than before or during crack use (36% vs. 21% and 12%, respectively). Two of these studies also assessed quantity of alcohol and cocaine use (Barrett et al., 2006;Gossop et al., 2006) and found that, on days in which both cocaine and alcohol were used together, participants reported an increase in average consumption of number of drinks (Barrett et al., 2006) and grams of cocaine (Gossop et al., 2006).
Those who specifically used crack cocaine, however, reported a decrease in number of average drinks and no significant change in amount of cocaine consumed (Gossop et al., 2006). Only one of these studies also investigated the order and sequencing of simultaneous cocaine and marijuana use: in a sample of university students, Barrett et al. (2006) found that, among those with lifetime co-use of cocaine and marijuana during a single session, 43% used marijuana before cocaine, while 37.5% used marijuana over multiple sessions with cocaine use. Changes in marijuana use quantity were not examined, however, due to non-standardized marijuana use units.
The studies that examined the order and sequencing of cocaine plus alcohol and/or marijuana use assessed simultaneous use with one of two methods: researchers either asked participants to describe (1) their typical patterns of use without specifying a time period (Macdonald et al., 2015) or (2) the number of days on which they used each substance over a specified time period (Barrett et al., 2005;Barrett et al., 2006;Gossop et al., 2006;Staines et al., 2001). Most used a version of the Timeline Followback (TLFB) to record days of use of each drug over a 30-or 90 day period. The TLFB was first developed as a self-report measure for retrospective estimates of alcohol use using a calendar format (Sobell et al., 1997(Sobell et al., , 1999 and has since been expanded to assess the use of multiple other substances (Goldstick et al., 2022;Martin-Willett et al., 2020;Rendina et al., 2015;Robinson et al., 2014). The TLFB has been compared with other clinical measures and biological measures and has demonstrated good reliability and validity (Eyawo et al., 2020;Martin-Willett et al., 2020). In addition to assessing frequency of concurrent and simultaneous use (i.e., days in which substances were used alone or together) and quantity of use on those days with a modified TLFB approach, these studies also examined order of ingestion by asking participants to describe the order in which cocaine was used with either alcohol or marijuana for each day of co-use (Gossop et al., 2006), the most recent day of co-use (Barrett et al., 2006), or their most typical day of use (Staines et al., 2001).
However, this method of enumeration of the order of substance use provides limited resolution regarding the duration, timing, and temporal proximity of episode-level simultaneous use on the specified day (Martin, 2008), and variations in selection of an anchor for recall between these studies (each day, most recent day, typical day) make comparisons difficult.
Given the limitations of the current literature, there is a significant need for methods that can assess detailed, temporal patterns of polysubstance use--including quantity, frequency, and duration of use--in order to inform treatment and prevention efforts. As part of a larger study, we developed and tested a new assessment that combines a calendar-based approach with a comprehensive, hour-byhour examination of within-day temporality for each use pattern to measure concurrent, sequential, and simultaneous polysubstance use in persons who use cocaine. To determine the reliability of this new assessment--the Polysubstance Use-Temporal Patterns Section (PSU-TPS)--we adopted a test-retest study design to examine the reliability of polysubstance use quantity, frequency, and duration measures, and assessed reasons for discrepancies.

| Sample
This analysis was based on data collected as part of a NIDA-funded study to identify patterns of human polysubstance use to guide the development of preclinical models (R21DA045140

| Assessments
The PSU-TPS was developed as a calendar-based interview followed by an hour-level examination of typical days of use for each pattern to collect information on the frequency, duration, quantity, preference, and order of the use of cocaine, alcohol, and marijuana. Module) is a fully structured diagnostic interview that assesses lifetime and past 12 month use and DSM-5 diagnostic criteria for a wide range of psychoactive substances and has demonstrated excellent reliability, as detailed in prior studies (Compton et al., 1996a(Compton et al., , 1996bCottler et al., 1989;Horton et al., 2000). For the purpose of this analysis, past 12-month DSM-5 cocaine, alcohol, and cannabis use disorders were examined, as well as other variables including age, sex, race/ethnicity, marital status, and education level.

| Test-retest procedures
Full interview procedures for both test and retest are shown in  Cottler et al., 1994Cottler et al., , 1997Cottler et al., , 2009) was administered after the retest interview to determine reasons for discrepancies in answers between the baseline and retest for selected PSU-TPS measures (including frequency of CAM, CA, and CM days, start and end times and route of cocaine use on a typical CAM/CA/CM day, and preferred drug use without considering accessibility). For each determined polysubstance use pattern, if the number of days in the past 30 days, duration of hourly use on a typical day, quantity of use on a typical day, or substance of preference differed between baseline and retest, participants were asked to explain the discrepancy by choosing one of 12 reasons such as not understanding the question, feeling too embarrassed to answer, or remembering differently between interviews.
All interviewers completed training and certification (provided by LBC and CWS, SAM authors and trainers) prior to administering the interviews. Participants were compensated $25 USD after the baseline and $25 USD after the retest interview for their time and effort, with a $10 USD bonus for being on time without having to reschedule.

| Analyses
To assess test-retest reliability for continuous variables, intra-class correlation coefficients (ICCs) were calculated along with their 95% confidence intervals. For categorical data, kappa tests were performed. For both ICCs and kappa values, ≥0.75 represents excellent reliability, values between 0.60 and 0.74 represent good reliability, values between 0.40 and 0.60 represent fair reliability, and values <0.40 represent poor reliability (Cicchetti, 1995).   Among the six use patterns measured, using CAM on the same day was the most common pattern, with 24 people endorsing at least one CAM day in the past 30 days. Therefore, we estimated the reliability of duration and quantity of use measures on a typical CAM day. Fair to good reliability was found for the duration of use of T A B L E 2 Responses at baseline and retest interviews and test-retest reliability of measured polysubstance use patterns (n = 48)

Baseline (mean) Retest (mean) ICC 95%CI
Number of   Reasons for discrepancies between baseline and retest interviews were also examined (Table 3). "Situation changed since the first interview" (e.g., participants reported cocaine use during a holiday at baseline, and at retest, the holiday was no longer within the past 30 days and not shown on the calendar) and "not remembering the same information" at each interview were the top reasons contributing to different responses for most of the variables. The start and end times of cocaine use on typical days when different polysubstance use of CAM, CA, or CM was endorsed had the highest discrepancies. For these variables, the respondent selecting a different typical day is another key reason why answers differed between two interviews. Among the 24 participants who reported past 30-day CAM use at both baseline and retest, 9 (37.5%) reported the same typical CAM day at both interviews, while 15 selected a different typical day.

| DISCUSSION
This study examined the test-retest reliability of the newly developed PSU-TPS, an assessment designed to collect temporal data on concurrent, sequential, and simultaneous polysubstance use among persons who use cocaine with alcohol and/or marijuana. This new assessment expands on past TLFB methods in its ability to evaluate detailed, hour-by-hour polysubstance use patterns, which is significant given that simultaneous and sequential polysubstance use is widespread but understudied. The PSU-TPS was found to have excellent reliability for assessing frequencies of concurrent polysubstance use patterns in the past 30 days, fair to good reliability for the duration of substance use on what participants identified as a typical cocaine-alcohol-marijuana polysubstance use day, and excellent reliability for quantity of alcohol use on typical polysubstance use days.
Similar to a multi-substance TLFB approach (Martin-Willett et al., 2020), the PSU-TPS begins with a calendar of the past 30 days and asks participants to endorse whether they used cocaine, alcohol, and/or marijuana on each day, which results in frequencies of daily polysubstance use patterns. Our reliability estimates for frequency of use in the past 30 days for cocaine, marijuana, and alcohol are similar to those reported by test-retest studies evaluating the reliability of frequency of days of cocaine (Ehrman & Robbins, 1994;Fals-Stewart et al., 2000;Robinson et al., 2014;Wray et al., 2016), marijuana (Fals-Stewart et al., 2000;Norberg et al., 2012;Robinson et al., 2014;Wray et al., 2016), and alcohol (Fals-Stewart et al., 2000;Wray et al., 2016) using a TLFB approach. After collecting data on polysubstance patterns on the past 30-day calendar, our assessment deviates from the traditional TLFB methods. Instead of only measuring the total quantity of use per day, our assessment asks participants to describe the hour-level start and end times for each episode of substance use on each typical day, as well as the quantity of use during each episode. Our assessment showed similar reliability estimates to TLFB approaches on mean drinks per day (Fals-Stewart et al., 2000). Since no TLFB approach to our knowledge assesses episode-level duration of substance use, we are unable to compare the reliability of our assessment for durations of use to prior studies.
An important feature of our test-retest study design was the inclusion of a Discrepancy Interview Protocol (DIP) (Cottler et al., 1994) at the end of the retest interview to assess reasons for discrepancies between the baseline and retest responses. The num- An additional challenge was measuring the reliability of the quantity of cocaine and marijuana used during substance use episodes. As is done in the SAM (Cottler et al., 1989), participants in the current study were given the option of reporting quantity of use for each episode in up to 25 different units. This flexibility allows participants to easily report the quantity according to their preferred units, but the variations in reported units limited our ability to examine the test-retest reliability for quantity of cocaine and marijuana used. While one option would have been to examine the reliability of quantity of use stratified by unit type (e.g., reliability among people who reported units in joints, grams, rocks, respectively), the sample size was not sufficiently large for these subgroup analyses.
Since analyses were conditional on participants endorsing at least one CAM, CA, or CM day at both baseline and retest, sample sizes were further reduced for reliability estimates of some polysubstance use characteristics. The utility of other methodological approaches for assessing quantity, including the use of a scale estimation procedure with a surrogate substance (Mariani et al., 2011;Norberg et al., 2012;Tomko et al., 2018) and visual scales (Cuttler & Spradlin, 2017;Farris et al., 2014) should be considered in future research. The issue of drug potency, which is not assessed in the PSU-TPS, also complicates the measurement of quantity for cocaine and marijuana and is an additional limitation. Lastly, though the order of the interview was carefully designed to ensure interview flow and questions on similar topics stayed together, the lack of randomization may have inadvertently caused potential order effects in participants responses.

| Conclusions
Our results demonstrate that detailed temporal patterns of concurrent, sequential, and simultaneous polysubstance use involving cocaine, alcohol, and marijuana can be reliably measured with the PSU-TPS. Future research should expand this assessment to detect polysubstance use patterns involving other substances, examine FITZGERALD ET AL.
-7 of 9 between-day fluctuations in use, explore the utility of other standardized measures of quantity and potency, and validate the assessment against similar tools (e.g., a multi-substance TLFB). The utilization of an hour-level analysis of the timing and order of polysubstance use will improve our understanding of the implications of sequential and simultaneous use patterns when combined with data on drug-related outcomes, which can help inform treatment and prevention efforts in this population.