Please proofread and polish the passage from an academic angle and highlight the modification:\nThe purpose of this research was to detect the changes of happiness, the ultimate pursuit of human being, in China, by examing happines inside Chinese brain (i.e., lay beleifs) and outside Chinese brain (i.e., natural languages). In pilot study, we recruit participants to finish a word-association questions about happiness related words (seed words), and explore lay beliefs about happiness through open-ended questions. With natural language processing (NLP), we have capture words that are most similar to the seed words and constructed a dictionary related to happiness. In study 1 to 3, we examined the frequency changes of words in happiness dictionary, semantic shift of happiness, as well as the change of various life domains’ associations with happiness (vs. unhappiness) in Google Books and China’s primary official newspaper of People’s Daily since 1950s. Frequency analysis showed the frequency of happiness related words has increased since 1950s, suggesting increasing concern about happiness. Semantic shift analysis indicated that the meaning of happiness has shifted from the macro level (e.g., collective events) to the micro level (e.g., individual experiences). Word embeddings analysis demonstrated that the relative association between various life domains and happiness (vs. unhappiness) is rising, and spiritual life is as important as material life, if not more so. These findings consistently suggest that there  The letter z should appear at least 25 times.
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