Most personality assessment instruments (despite being loosely referred to as "personality tests") are in fact introspective (i.e., subjective) self-report questionnaire (Q-data, in terms of LOTS data) measures or reports from life records (L-data) such as rating scales.

[4][5] A major problem with both L-data and Q-data methods is that because of item transparency, rating scales, and self-report questionnaires are highly susceptible to motivational and response distortion ranging from lack of adequate self-insight (or biased perceptions of others) to downright dissimulation (faking good/faking bad) depending on the reason/motivation for the assessment being undertaken.

[6][7][8] The first personality assessment measures were developed in the 1920s[9] and were intended to ease the process of personnel selection, particularly in the armed forces.

[13] However, the Big Five and related Five Factor Model have been challenged for accounting for less than two-thirds of the known trait variance in the normal personality sphere alone.

Based on the lexical hypothesis, Galton estimated the number of adjectives that described personality in the English dictionary.

[19] Galton's list was eventually refined by Louis Leon Thurstone to 60 words that were commonly used for describing personality at the time.

[22] Of the many introspective (i.e., subjective) self-report instruments constructed to measure the putative Big Five personality dimensions, perhaps the most popular has been the Revised NEO Personality Inventory (NEO-PI-R)[19] However, the psychometric properties of the NEO-PI-R (including its factor analytic/construct validity) has been severely criticized.

The self-report inventory involves administration of many items requiring respondents to introspectively assess their own personality characteristics.

[28] Test items are then selected or eliminated based upon which will result in the strongest internal validity for the scale.

The clearly defined and face valid questions that result from this process make them easy for the person taking the assessment to understand.

Although subtle items can be created through the deductive process,[29] these measure often are not as capable of detecting lying as other methods of personality assessment construction.

[30] Advanced statistical methods include the opportunity to discover previously unidentified or unexpected relationships between items or constructs.

It also may allow for the development of subtle items that prevent test takers from knowing what is being measured and may represent the actual structure of a construct better than a pre-developed theory.

[31] Criticisms include a vulnerability to finding item relationships that do not apply to a broader population, difficulty identifying what may be measured in each component because of confusing item relationships, or constructs that were not fully addressed by the originally created questions.

Combining the scores of a self-report and an observer report can reduce error, providing a more accurate depiction of the person being evaluated.

The observations can take place in a natural (e.g., a schoolyard) or artificial setting (social psychology laboratory).

Direct observation can help identify job applicants (e.g., work samples[34]) who are likely to be successful or maternal attachment in young children (e.g., Mary Ainsworth's strange situation).

[36] The idea behind these personality tests is that employers can reduce their turnover rates and prevent economic losses in the form of people prone to thievery, drug abuse, emotional disorders or violence in the workplace.

[38] Despite evidence showing personality tests as one of the least reliable metrics in assessing job applicants,[39] they remain popular as a way to screen candidates.

Dimensional approaches such as the Big 5 describe personality as a set of continuous dimensions on which individuals differ.

[48][49] Work in experimental settings[50] has also shown that when student samples have been asked to deliberately fake on a personality test, they clearly demonstrated that they are capable of doing so.

Forced choice (ipsative testing) has three formats: PICK (selecting a best fitting statement), MOLE (selecting a most and least fitting statement), and RANK (a most to least alike ranking), the effectiveness of using forced choice to prevent faking is inconclusive.

[54] The MBTI questionnaire is a popular tool for people to use as part of self-examination or to find a shorthand to describe how they relate to others in society.

It is well known from its widespread adoption in hiring practices, but popular among individuals for its focus exclusively on positive traits and "types" with memorable names.

[55] Due to the publisher's strict copyright enforcement, many assessments come from free websites which provide modified tests based on the framework.

In particular Buzzfeed became well known for publishing user-created quizzes, with personality-style tests often based on deciding which pop culture character or celebrity the user most resembles.

[58] There is an issue of privacy to be of concern forcing applicants to reveal private thoughts and feelings through his or her responses that seem to become a condition for employment.

In particular, ipsative personality tests are often misused in recruitment and selection, where they are mistakenly treated as if they were normative measures.

[61] Also, brain scan technology has dramatically improved, which is now being developed to analyze personalities of individuals extremely accurately.

[61] Also, this allows for the analysis of large amounts of data that was difficult or impossible to reliably interpret before (for example, from the internet).