PT - JOURNAL ARTICLE AU - Michael Theobald TI - On estimating betas that change AID - 10.3905/jpm.1982.408894 DP - 1982 Oct 31 TA - The Journal of Portfolio Management PG - 62--65 VI - 9 IP - 1 4099 - https://pm-research.com/content/9/1/62.short 4100 - https://pm-research.com/content/9/1/62.full