Evidence Levels
Every research record on this site is assigned an evidence tier (1–4) and an evidence-strength label (High / Medium / Low / Uncertain). This page explains what those mean.
The four tiers
| Tier | What it is | Examples |
|---|---|---|
| Tier 1 | Clinical guidelines and international classifications produced by authoritative bodies. | The WHO ICD-11, the APA DSM-5. |
| Tier 2 | Peer-reviewed studies and reviews published in scientific journals. | Systematic reviews, meta-analyses, cross-sectional studies, neuroimaging studies. |
| Tier 3 | Weaker forms of evidence: clinical reports, case series, and non-peer-reviewed analyses. | Clinical reports on PIED, narrative reviews with limited rigor. |
| Tier 4 | Community observation and personal anecdote. | Recovery-community reports, forum accounts. |
Two separate dimensions
Phase 2 assessment separates what kind of source something is from how strong the evidence is. A clinical guideline is a strong source type for some questions, but no source type automatically makes every claim strongly supported.
Source type
| Source type | Example |
|---|---|
| Diagnostic classification | WHO ICD-11, APA DSM-5 |
| Clinical guideline | Professional organization treatment guidance |
| Systematic review / meta-analysis | Quantitative synthesis of studies |
| Randomized controlled trial | Experimental comparison |
| Cohort / cross-sectional study | Observational research |
| Neuroimaging study | Brain correlates (correlational) |
| Case report / qualitative study | Individual or thematic accounts |
| Community report | De-identified experience (not evidence of causation) |
Evidence strength
| Strength | Meaning |
|---|---|
| Strong | Multiple consistent, high-quality sources |
| Moderate | Reasonable support with meaningful gaps |
| Limited | Few studies, small samples, or indirect evidence |
| Mixed | Conflicting findings across studies |
| Uncertain | Insufficient evidence to judge |
Community reports are useful for generating questions and identifying recurring experiences — never for establishing medical causation.
Evidence-strength labels
- High — a consensus classification or a large, high-quality synthesis.
- Medium — a peer-reviewed study or review with meaningful limitations.
- Low — weak, contested, or non-peer-reviewed evidence.
- Uncertain — evidence is missing, mixed, or cannot support a conclusion.
How to judge evidence for yourself
When you encounter a claim about pornography use, ask:
- What is the source? A peer-reviewed study, a clinical guideline, a blog post, or a forum comment?
- Was there a comparison? Does the evidence compare a group of interest to a control group, or is it only a set of anecdotes?
- Is causation being claimed? Many studies are cross-sectional and can only show association, not cause and effect.
- Who was studied? Small, self-selected, or treatment-seeking samples may not generalize.
- Has it been replicated? A single study — especially a small one — is rarely enough to establish a fact.
Tier and strength reflect the kind and quality of evidence, not whether a topic is important. Community experience can be valuable for generating questions and patterns, but it never counts as scientific evidence. See what remains debated.