🧠AP Psychology
Using the source provided, respond to all parts of the question.
1. Your response to the question should be provided in six parts: A, B, C, D, E, and F. Write the response to each part of the question in complete sentences. Use appropriate psychological terminology in your response.
Identify the research method used in the study.
State the operational definition of sleep efficiency in the study.
Describe the relationship between daily caffeine intake and sleep efficiency as indicated by the correlation coefficient.
Identify the ethical guideline regarding data handling that the researchers followed.
Explain the extent to which the research findings may or may not be generalizable to the general adult population using specific and relevant evidence from the study.
Explain how the research findings support or refute the concept of caffeine acting as an antagonist.
Sleep disturbances among university students have become increasingly prevalent, with emerging research suggesting that daily consumption patterns of psychoactive substances may play a critical role in sleep quality deterioration over time. This longitudinal investigation examines how daily caffeine consumption relates to sleep efficiency across an academic year, drawing upon circadian rhythm theory and the adenosine receptor antagonism model to understand the cumulative effects of stimulant use on sleep architecture.
Total N: 186
Recruitment: Participants were recruited through campus-wide emails, flyers posted in residence halls, and announcements in introductory psychology courses at a mid-sized public university in the Midwest. Students who expressed interest completed an initial screening survey to confirm they were enrolled full-time and had no diagnosed sleep disorders. A total of 186 undergraduates enrolled at baseline (Time 1), with 157 participants retained at the 6-month follow-up (Time 2), and 134 participants completing the final 12-month assessment (Time 3), reflecting a 28% attrition rate across the study duration. Attrition was primarily attributed to students transferring institutions, graduating early, or withdrawing due to time constraints.
Gender: 58% women, 39% men, 3% non-binary or gender diverse¹
Race/Ethnicity: 62% White, 18% Asian, 11% Hispanic/Latino, 6% Black/African American, 3% multiracial or other
Age Range: 18-24 years
Age Mean: 19.4
Age SD: 1.2
Compensation: Participants received a $15 gift card at each time point ($45 total for full completion) and were entered into a raffle for one of four $100 prizes at study conclusion.
Caffeine Consumption Questionnaire (CCQ): A validated 14-item self-report measure assessing daily intake from all sources including coffee, tea, energy drinks, soft drinks, and caffeine supplements
Actigraphy devices (Actiwatch Spectrum Plus): Wrist-worn accelerometers used to objectively measure sleep patterns over 14-day periods at each assessment wave
Sleep diary logs: Standardized daily logs where participants recorded bedtime, wake time, and perceived sleep quality
Pittsburgh Sleep Quality Index (PSQI): Standardized questionnaire measuring subjective sleep quality over the previous month
Demographic and lifestyle questionnaire: Collected information on academic major, living situation, work hours, and substance use
At baseline (Time 1, September), participants attended an in-person orientation session where they provided informed consent, completed demographic questionnaires, and received training on using actigraphy devices and sleep diaries.
Participants wore actigraphy devices continuously for 14 days and completed daily sleep diaries and caffeine consumption logs each morning within 30 minutes of waking.
After the 14-day monitoring period, participants returned devices and completed the PSQI and CCQ in a supervised laboratory session lasting approximately 45 minutes.
At the 6-month follow-up (Time 2, March), participants were recontacted via email and text message, re-consented to continued participation, and repeated the identical 14-day monitoring protocol and questionnaire battery.
At the 12-month follow-up (Time 3, September of the following academic year), the same procedures were administered to track changes across a full academic cycle.
Throughout the study, research assistants sent daily reminder texts during monitoring periods and conducted brief check-in calls at 3 and 9 months to maintain participant engagement and address any device issues.
Participants were reminded at each time point of their right to withdraw from the study at any time without penalty or loss of compensation for completed portions.
Daily caffeine intake was operationally defined as the total milligrams of caffeine consumed per day, calculated by summing all reported caffeine sources using standardized caffeine content values (e.g., 95 mg per 8 oz coffee, 47 mg per 8 oz tea, 80 mg per 8 oz energy drink) and averaging across the 14-day monitoring period. Sleep efficiency was operationally defined as the percentage of time spent asleep while in bed, calculated by dividing total sleep time (in minutes) by total time in bed (in minutes) and multiplying by 100, as measured objectively by actigraphy devices across the 14-day monitoring period at each time point.
Informed consent was obtained at baseline and re-confirmed at each subsequent time point, with participants explicitly reminded of their right to withdraw from the study at any time without penalty. All data were de-identified using participant codes, and actigraphy data were stored on encrypted, password-protected servers accessible only to approved research personnel.
Longitudinal analyses revealed that daily caffeine consumption increased significantly over the 12-month study period, rising from 142.3 mg at baseline to 224.1 mg at Time 3—an increase of approximately 58%. Concurrently, sleep efficiency declined from 87.2% at baseline to 78.4% at the 12-month follow-up, representing a decrease of 8.8 percentage points. Mixed-effects modeling indicated that within-person increases in caffeine consumption were significantly associated with within-person decreases in sleep efficiency across time points (β = -0.19, p < .001), suggesting that as individual students consumed more caffeine, their sleep efficiency correspondingly deteriorated.
Measure | Time 1 (Baseline) | Time 2 (6 months) | Time 3 (12 months) |
|---|---|---|---|
Daily Caffeine Intake (mg) | M = 142.3, SD = 68.5 | M = 189.7, SD = 82.4 | M = 224.1, SD = 91.2 |
Sleep Efficiency (%) | M = 87.2, SD = 5.8 | M = 82.6, SD = 7.3 | M = 78.4, SD = 8.9 |
Total Sleep Time (hours) | M = 7.1, SD = 0.9 | M = 6.5, SD = 1.1 | M = 6.0, SD = 1.3 |
Sample Size | N = 186 | N = 157 | N = 134 |
The findings demonstrate a concerning pattern wherein caffeine consumption increases progressively throughout the undergraduate experience while sleep efficiency simultaneously declines, consistent with circadian rhythm theory² which posits that caffeine's antagonism of adenosine receptors disrupts the homeostatic sleep drive and delays circadian phase. This reciprocal relationship may create a problematic cycle: students consume more caffeine to compensate for poor sleep, which in turn further degrades sleep quality. The longitudinal design allows us to observe these developmental changes within the same individuals over time, though the predominantly White sample from a single Midwestern institution limits generalizability to more diverse student populations or universities in different geographic regions with varying campus cultures around stimulant use.
Hernandez, R. M., Okonkwo, J. A., & Chen, L. (2023). Tracking the relationship between caffeine consumption and sleep efficiency in undergraduates: A 12-month longitudinal study. Journal of Sleep Research and Health Psychology, 41(3), 287-304. https://doi.org/10.1016/j.jsrhp.2023.04.012
- Gender categories reflect participants' self-identification. The terminology used in this article follows APA guidelines for inclusive language regarding gender identity and expression.
- Circadian rhythm theory refers to the biological framework explaining how internal 24-hour cycles regulate sleep-wake patterns, with adenosine accumulation during waking hours creating sleep pressure that caffeine temporarily blocks through receptor antagonism.
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