[1] A Review of General Psychology survey, published in 2002, ranked Meehl as the 74th most cited psychologist of the 20th century, in a tie with Eleanor J.

[3] He earned his bachelor's degree in 1941[4] with Donald G. Paterson as his advisor, and took his PhD in psychology at Minnesota under Starke R. Hathaway in 1945.

In 1995, Meehl was a signatory of a collective statement titled "Mainstream Science on Intelligence", written by Linda Gottfredson and published in the Wall Street Journal.

Behaviorists and operationists would have rejected as unscientific any notion that there was some general thing called "intelligence" that existed inside a person's head and that might be reflected almost-equivalently in Stanford-Binet IQ tests or Wechsler scales.

[14] Influenced by and in respect of Popper's asymmetry principle,[15] Meehl was a strident critic of using statistical null hypothesis testing for the evaluation of scientific theory.

He believed that null hypothesis testing was partly responsible for the lack of progress in many of the "scientifically soft" areas of psychology (e.g. clinical, counseling, social, personality, and community).

Researchers who guessed randomly at the sign of any small effect would have a 50–50 chance of finding confirmation with sufficiently large sample size.

Individuals who endorsed the K scale items were thought to be demonstrating a sophisticated attempt to conceal information about their mental health history from test administrators.

[29] Meehl argued that mechanical methods of prediction, when used correctly, make more efficient and reliable decisions about patient prognosis and treatment.

[29] Within his view, mechanical prediction approaches need not exclude any type of data from being combined and could incorporate coded clinical impressions.

Once the clinical information is quantified, Meehl proposed mechanical approaches would make 100% reliable predictions for exactly the same data every time.

[32][33] In response to objections, Meehl continued to defend algorithmic prediction throughout his career and proposed that clinicians should rarely deviate from mechanically derived conclusions.

[4] Meehl argued schizophrenia should be considered a genetically based neurological disorder manifesting via complex interactions with personal and environmental factors.

[36][38][39] The schizogene would manifest on the cellular level throughout the central nervous system and should be observed as a functional control aberration called hypokrisia.

Cells exhibiting hypokrisia should contribute to a characteristic pattern of impaired integrative signal processing across multiple neural circuits in the brain, which Meehl termed "schizotaxia".

In response to typical rearing environments and social reinforcement schedules, this neural aberration should invariably lead to a collection of observable behavioral tendencies called "schizotypy".

Schizotypy indicators would include neurological soft signs, subtle differences in language usage ("cognitive slippage"), and effects on personality and emotion.

Schizophrenia would only occur when individuals are carrying other non-specific genetic risk factors ("polygenic potentiators") relevant for traits such as anhedonia, ambivalence, and social fear.

[40] His theorizing increased interest in longitudinal study of individuals at risk for psychosis and family members of people with schizophrenia who may be carrying the schizogene.

[43][44] With the help of several colleagues, Meehl developed multiple statistical methods for identifying the presence of categorical groupings within biological or psychological variables.

[46] Although many DSM-defined psychiatric syndromes can be reliability identified in clinical settings, Meehl argued that the categorical nature of mental illnesses assumed by these diagnoses (i.e., a person is either sick or well) should be tested empirically rather than accepted at face value.

Meehl advocated for a data-driven approach that could, in the words of Plato, "carve nature at its joints", and determine when it is most appropriate to conceptualize something as being categorical or continuous/dimensional.

[citation needed] In his writings, Meehl advocated for the creation of a field called "taxometrics" to test for categorical groupings across diverse scientific disciplines.

Meehl envisioned applying taxometric approaches when the precise underlying latent causes are currently unknown and only observable "indicators" are available (e.g., psychiatric conditions).

[citation needed] Coherent Cut Kinetics is the suite of statistical tools developed by Meehl and his colleagues to perform taxometric analysis.

"Coherent" refers to the process of using multiple indicators and metrics together to make a case for convergence about the categorical or dimensional nature of the phenomenon being studied.

[52] In line with Meehl's theorizing, studies using taxometric methods have demonstrated how most psychiatric conditions are better conceptualized as being dimensional rather than categorical[53] (e.g., psychopathy,[54][55] posttraumatic stress disorder,[56] and clinical depression[57]).

In contrast, he recalled numerous interesting illuminating case conferences within internal medicine or neurology departments, which often centered around pathologist reports and objective data about patients' pathophysiology.

In other words, case conferences outside mental health disciplines were benefiting from including objective evidence against which clinical expertise could be compared and contrasted.

He encouraged clinicians to be humble when collaborating about patient care and pushed for a higher scientific standard for clinical reasoning in mental health treatment settings.