Placebo and Expectancy Effects in Wellness Tracking

Why this matters for trackers

A tracker gives you a number or a verdict, such as a sleep score or "readiness". Reading that verdict can change how you feel and act. This page explains placebo, nocebo and expectancy effects and what research has found. It is information only and does not diagnose or advise on your own health.

Evidence labels used here: established (many consistent studies), mixed, insufficient evidence, Proper evidence not found (we looked and found no usable study), and marketing claim.

Plain definitions

• Placebo effect. The US National Center for Complementary and Integrative Health describes it as a beneficial health outcome resulting from a person's anticipation that an intervention will help. How a provider interacts with a patient can also bring about a response independent of any specific treatment. [1]
• Nocebo effect. The opposite: expecting something to go badly can contribute to feeling worse. In wellness tracking this might look like feeling more tired after seeing a low score.
• Expectancy. What you believe a product or practice will do, before or while you use it.

What research shows about placebo in general

A Cochrane review of placebo interventions did not find that placebos have important clinical effects in general. It did find that placebo can influence patient-reported outcomes, especially pain and nausea, and that it is hard to tell a real patient-reported effect from biased reporting. [2] For insomnia, the review found no statistically significant placebo effect, though confidence intervals were wide. [2]

Because people often improve on their own, a later analysis of three-armed trials found that spontaneous improvement and placebo each contributed importantly to change seen in actively treated people. [3]

Label: mixed. Placebo effects are real in some settings, mostly for symptoms people report themselves, and are smaller or unclear elsewhere.

What a sleep-quality experiment found

In two studies of 164 participants, volunteers were told, with no device involved, that they had spent either a high or a low share of the night in REM sleep. The sleep quality they were assigned predicted performance on two cognitive tasks, while their own report of how they slept did not. [4] The authors concluded that mindset can influence cognitive states in both positive and negative directions. [4]

Label: promising but limited. The study used invented feedback, not a real tracker, and tested only a few tasks. It does not show that any specific product has this effect.

Trackers and sleep worry

Clinicians have described patients seeking treatment for self-diagnosed sleep problems based on light or restless sleep seen on their tracker, and who feel tracker data matches their experience more than validated methods. [5] A survey of 523 adults in one study estimated orthosomnia, a pattern of tracker-related sleep preoccupation, at between 3.0% and 14.0% depending on how strictly it was defined; the design could not show that trackers caused it. [6] For more, see Orthosomnia and Sleep-Tracking Anxiety.

Proper evidence not found: we searched PubMed and Europe PMC for randomized trials testing whether showing people false or altered readings from a consumer wearable changes their symptoms or performance, and did not find one we could read. Claims that a particular device produces a "placebo" or "nocebo" response are therefore untested for most products.

Accuracy is not benefit

A reading can be accurate and still not help you, and a reading can be unreliable and still change how you feel. The American Academy of Sleep Medicine said that consumer sleep technologies lack validation and FDA clearance and cannot be used to diagnose or treat sleep disorders at this time. [7] See Consumer Sleep Tracking vs Clinical Sleep Study.

Practical reading habits

• Notice how a score makes you feel before you check how you actually slept or felt.
• Remember a good result after starting something new can partly reflect hope or ordinary improvement. See Correlation vs Causation in Personal Data.
• If worry about numbers is affecting sleep or mood, talk with a clinician rather than adding more tracking. [5]