ST StudyTrace Research studies on iPhone and Android
Privacy Policy

Privacy for StudyTrace

Effective date: October 2, 2026. This policy explains how the StudyTrace iPhone and Android apps handle participant data, permissions, and study-related information. Study-specific consent terms provided by the research team remain in effect.

1. Overview

StudyTrace is a research data collection app used to support studies run by research teams, universities, labs, or other approved study operators. The app is intended to collect only the streams enabled for a specific study and only after the participant has consented and granted the required device permissions.

In many cases, the research team that invited you to the study is the primary data controller for study data. If you have a question about a specific study, consent document, data request, or withdrawal procedure, you should also contact the study coordinator who invited you.

2. Data We May Collect

Depending on the study configuration and permissions you approve, StudyTrace may collect the following categories of data:

  • Study enrollment information such as the secure study URL or study configuration needed to join a study.
  • Location data, including background location, when a study enables mobility or context sensing.
  • Survey and experience sampling responses, including multiple photos that you choose from your library or take with your camera on iPhone and Android. StudyTrace re-encodes selected images to remove original EXIF/GPS metadata.
  • When enabled by the study, outdoor weather estimates (temperature, humidity, apparent temperature, wind, precipitation, cloud cover, weather code, and solar radiation), plus sunrise, sunset, and day length. The research server sends coordinates rounded to 0.01 degrees to Open-Meteo (open-meteo.com). Personal light and indoor exposure sensing are disabled for the current protocol; older ambient-light records may remain in study exports.
  • When the study separately enables air pollution, outdoor model estimates of PM2.5, PM10, carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone, and US/European air quality indices from Open-Meteo and the Copernicus Atmosphere Monitoring Service (CAMS). The server sends the same rounded GPS coordinates to Open-Meteo's air-quality API. These are area estimates, not indoor or personal pollution measurements.
  • When separately enabled, GPS-based land-cover context from ESA WorldCover 2021 map tiles hosted on AWS. The server reads small map sections and computes vegetation, tree, cropland, built-up, and water percentages within 300 metres of a location rounded to 0.001 degrees. Tile URLs and byte-range requests contain no participant identifiers or coordinate parameters, but identify requested map areas. This historical map does not establish a current park visit.
  • When separately enabled, five brief survey items about current setting, perceived noise, temperature sensation, recent outdoor time, and green-space contact. These are participant reports. No microphone audio is collected for the noise question.
  • On Android, app package names, app labels, foreground-use duration, launch counts, and screen lock or unlock events when you grant Usage Access.
  • On iPhone, device-usage context from Battery usage screenshots that you choose to upload as survey photo responses.
  • Technical and device identifiers needed for app operation, syncing, notifications, logging, and study delivery.
  • Push notification token information so the app can receive survey reminders or study updates.
  • On supported platforms, optional motion, health, calendar, contacts, or Bluetooth-related data if a study enables those features and you grant permission.

The exact set of collected data depends on the study you join. Not every study uses every available sensor or permission.

Battery usage screenshot collection is optional and study-specific. When enabled, StudyTrace asks you to open iPhone Settings → Battery → View All Battery Usage, take a screenshot, and upload that screenshot through a survey photo question. StudyTrace does not silently export Apple's Screen Time database.

If Battery screenshots are enabled, the secure server may use OCR to extract app names, screen-time text, and battery percentages from screenshots you submit. These records are collected for research analysis only.

3. Permissions

StudyTrace may request permission to access capabilities such as:

  • Location services
  • Notifications
  • Android Usage Access for app foreground-use and screen-state research data
  • Photos or camera access on supported platforms for optional survey attachments, including Battery usage screenshots when requested by a study
  • Motion and fitness data
  • Health data
  • Calendar, contacts, or Bluetooth

Denying a permission may limit some study features. StudyTrace is designed so collection starts only after consent, and permission prompts are tied to the features your study needs.

You can decline to upload a Battery screenshot or skip the survey question when the study protocol allows it.

4. How Data Is Used

StudyTrace uses data to:

  • Deliver study participation features such as enrollment, reminders, and surveys.
  • Collect research data approved by the study protocol or consent materials.
  • Upload study data to the research server or backend configured for that study.
  • Maintain app reliability, debug syncing issues, and support participant operations.

StudyTrace is not intended to use participant data for third-party advertising, profiling, sale of data, or cross-app tracking. Battery screenshot-derived app-usage data is used only for the study purpose described by the research team.

5. Sharing and Storage

Data collected by StudyTrace may be stored locally on your device and then synced to the backend configured by the study operator. That backend may be managed by a university, research lab, cloud provider, or another approved operator.

  • Data may be shared with the research team responsible for the study you joined.
  • Technical service providers may process data only to the extent needed to host, sync, or maintain the app and study backend.
  • StudyTrace is designed to connect to study servers using secure HTTPS connections.

The exact server location, institutional ownership, and retention schedule may vary by study. Those details should be described in the study consent materials.

6. Retention and Withdrawal

StudyTrace allows participants to leave a study from within the app. Leaving stops collection, clears queued study data and local study settings, and lets the participant ask the configured research server to delete data previously uploaded by that device.

A deletion request may be retried when the device is back online. Study-specific consent terms and applicable research-retention rules may affect what the research team is legally permitted or required to retain. For deletion, correction, or access questions, contact the study coordinator.

7. Children

StudyTrace is not directed to children unless a specific study is designed for that population and appropriate parental consent or legal authorization has been obtained by the research team.

8. Changes to This Policy

This privacy policy may be updated as StudyTrace evolves or as app-store, legal, or study requirements change. The effective date at the top of this page will be updated when changes are published.

9. Contact

For general app information, see liu-chao.site or the maintainer profile at github.com/chaoliu-cl.

For study-specific questions, consent issues, withdrawal requests, or questions about how your research data is handled, contact the study coordinator or research team that invited you to the study.