{"id":2877,"date":"2022-07-23T16:35:25","date_gmt":"2022-07-23T14:35:25","guid":{"rendered":"https:\/\/www.psyctc.org\/psyctc\/?p=2877"},"modified":"2022-07-23T21:23:43","modified_gmt":"2022-07-23T19:23:43","slug":"sometimes-n4-is-enough","status":"publish","type":"post","link":"https:\/\/www.psyctc.org\/psyctc\/2022\/07\/23\/sometimes-n4-is-enough\/","title":{"rendered":"Sometimes n=4 is enough"},"content":{"rendered":"\n

Back in 2002, with two colleagues, I published a paper:

Evans, C., Hughes, J., & Houston, J. (2002). Significance testing the validity of ideographic methods: A little derangement goes a long way<\/em>. British Journal of Mathematical and Statistical Psychology, 55(2), 385\u2013390. https:\/\/doi.org\/10.1348\/000711002760554525<\/a>. <\/p>\n\n\n\n

Contact me<\/a> if you’d like a copy!<\/p>\n\n\n\n

In the paper we used a bit of old maths to show a simple way of validating idiographic\/ideographic data. The data in question were principal component plots of person repertory grids created by six patients in a prison psychotherapy group (who gave permission for this). These plots are completely personal to each individual. They depend on the elements the patients chose for the roles in the grid (e.g. victim, brother, boss, ideal self) and the constructs on which they chose to rate them, (e.g. aggressive, caring, selfish) and the ratings they gave each element. <\/p>\n\n\n\n

Those principal component plots represent the best two dimensional plot of all the ratings for each grid. Julia (Houston) had asked the two therapists if they could map the six plots back to the patients. As we said in the paper:
Both therapists matched four of the six pre-therapy grids successfully; one therapist matched all six post-therapy grids and the other matched three of the six. We sought to assess the probabilities that these matchings might have been achieved by chance alone. This paper reports the logic which shows that this probability was lower than a conventional criterion of significance ( p < 0.05) where four or six grids were matched correctly.<\/em><\/p>\n\n\n\n

This is a completely general method, the steps are:<\/p>\n\n\n\n