Self-reports are the most widely used method of assessing personality, primarily due to their convenience. While self-reported personality is useful for understanding how a person perceives themselves, on its own, this form of assessment often provides more insight into a candidate’s self-perception than it provides into their actual personality. 

When completing a self-report, people are typically consciously aware of what is being measured and the questions that are measuring it. This conscious awareness allows assessment-takers to regulate their responses, leading to biases in self-reporting. For example, "social desirability bias" is common in self-reports, where people tend to answer questions in ways that make them look good rather than answering truthfully.

Self-reports are also subjective, in that they rely on and assess one’s point of view. The subjective nature of self-reports often results in "reference-group effects," where a person’s perception of themselves is biased by the degree to which they compare themselves to other people. For instance, an individual may think of themselves as extraverted if the people they surround themselves with are extremely introverted. 

Research has shown that language can be an objective behavioural measure of personality. Function words, in particular, are used largely unconsciously, which makes them an ideal implicit measure of behaviour and provides an approach that helps mitigate the biases inherent in self-reports.

Research also shows that people use similar language patterns over time and throughout different contexts, which makes language a reliable measure for understanding personality traits and differences among individuals. For example, people who score higher on extraversion typically use more language indicative of positive emotion and social topics.

Language-based assessment also has another unique advantage: You can analyze anyone's personality without their participation - simply by analyzing their language from social media, interviews, speeches, Zoom and MS Meet transcripts, call center call recordings, earning calls, or anywhere they are communicating. Here's an example of a personality assessment of the CEOs of two publicly traded companies that was conducted by analyzing earnings call transcripts. 

In summary, language analysis is a valid and effective way of understanding and measuring personality. People’s language-based personality may not match their self-reported personality because self-reports evaluate how a person perceives themselves, while language measures how they really behave. 

Read more about language-based personality here.