Their post- test performance might be affected by this learning experience that occurred while they took the pretest. Statistical regression is another threat that oc- curs only if participants are selected on the basis of their extreme scores.
The prime minister of Ghana was the head of government of Ghana from 1957 to 1960 and again from 1969 to 1972. Wikipedia First holder: Kwame Nkrumah Abolished: 13 January 1972 Final holder: Kofi Abrefa Busia
