Registration for this round started in October 2018 and ended in January 2019.
After discarding bad and invalid entries (for example, those using disposable email addresses), this round had 4070 entries that were matched into 2035 pairs.
The matching survey for this round had 77 personality questions and 13 knowledge questions that were used to compute scores on 14 traits (12 of personality and 2 of knowledge). The goal for matching was to put all persons into pairs so that the similarity in psychological traits between the members of each pair was maximized.
Similarity was measured as the Pearson correlation between the pair's traits. So a similarity score of 1 means that the scores were the exact same, and a score of -1 means that scores were the exact opposite (the scores reported in the email have been multiplied by 100 to be easier to read though, so a score of 50 = 0.5 correlation, etc.).
The graph below shows the distribution of similarity scores for all the matched pairs that were mailed out this round, versus what similarity scores would have been if the matches had been made at random.