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HARKing (Hypothesizing After Results are Known)

Also Known As: Post-hoc hypothesis revision Retrospective hypothesizing
Statistical Error ID: harking

Definition

HARKing is the practice of presenting a hypothesis that was developed or refined after examining the data as though it had been formulated before data collection. This transforms exploratory analysis into what appears to be confirmatory research, creating a false impression that a specific prediction was confirmed. HARKing inflates the apparent evidential value of findings because post-hoc hypotheses are fitted to the data and therefore almost guaranteed to be supported by it.

Examples

A researcher studies the effect of a drug on 20 health outcomes. Only the effect on blood pressure is statistically significant. The published paper presents a focused hypothesis about blood pressure, with no mention of the other 19 outcomes tested, making it appear as though the drug's blood pressure effect was the predicted finding all along.

A marketing team runs an A/B test on five different ad designs and measures click-through rates, purchase conversions, and time-on-page. Only one metric — time-on-page — differs significantly for one ad variant. The final report is presented to leadership with the confident headline 'We hypothesized that Ad Variant C would boost user engagement,' framing a post-hoc observation as a planned prediction.

A sociologist collects survey data on 30 demographic and attitudinal variables, then runs correlations across all of them. She notices that people who own houseplants report slightly higher life satisfaction. She writes up the finding with an introduction citing theories of biophilia and human-nature connection, presenting it as a theoretically motivated hypothesis rather than a pattern she stumbled upon while data-mining.

Verification Steps
Verification Steps
Binary yes/no questions that an AI must answer to detect a reasoning pattern in a text.
Each of the 452 aspects has verification steps — simple yes/no questions designed to systematically detect whether a pattern appears in a text. For ad hominem: "Does the argument attack a person rather than their claim?" For false dichotomy: "Are only two options presented when more exist?" This ensures consistent, reproducible analysis.

Binary (yes/no) questions an LLM must answer to identify this aspect:

  1. 1

    Does the study present a hypothesis that fits the observed results suspiciously well?

    Type: binary
  2. 2

    Was the hypothesis plausibly formulated after seeing the data rather than before?

    Type: binary
  3. 3

    Is there a registered pre-analysis plan or pre-registration that confirms the hypothesis was stated a priori?

    Type: binary
  4. 4

    Does the narrative present exploratory findings as if they were confirmatory?

    Type: binary
Deep Dive
The expandable detail section on each aspect page with examples, psychology, and counter-strategies.
The Deep Dive section provides in-depth information about each aspect: a real-world example showing the pattern in action, an explanation of why it works psychologically, practical advice on how to counter it, alternative names, and links to related aspects.

Hierarchical Context