For more context, the passage in Al-Krenawi & Graham (2006) reads as follows on page 12.
Previous research suggests that education and attitudinal acceptance of polygamy are inversely correlated (Heaton & Hirschl, 1999; Maziak et al., 2002; Nevadomsky, 1991); other findings are less conclusive (Nevadomsky, 1991). The Bedouin-Arab community is in a massive state of transition, part of which includes higher attainment for youth. Respondents in monogamous marriages therefore may have had greater opportunity for education; and the potential for less acceptance of polygamy may be modestly influential on the cohort.
My interpretation is that research indicated by 3 papers suggests that where education is high, acceptance of polygamy is low, and where education is low, acceptance is high. The acceptance is shown through attitude.
As @ArnonWeinberg pointed out, "attitude" would normally refer to "expressed attitude" measured via a survey or interview or similar report. In this case it was questionnaires.
Questionnaires were structured; data collectors were present during the interview, completed the questionnaire forms with the respondent and, for those with limited reading or writing skills, the researchers read to the respondent and filled in the questionnaire according to the given responses (pages 7—8).
Heaton, T., & Hirschl, T. A. (1999). The trajectory of family change in Nigeria. Journal of Comparative Family Studies 30(1), 35-55. Retrieved from http://www.jstor.org/stable/41603608
Al-Krenawi, A., & Graham, J. R. (2006). A comparison of family functioning, life and marital satisfaction, and mental health of women in polygamous and monogamous marriages. International Journal of Social Psychiatry, 52(1), 5-17. DOI: 10.1177/00207640060061245
Maziak, W., Asfar, T., Mzayek, F., Fouad, F. M., & Kilzieh, N. (2002). Socio-demographic correlates of psychiatric morbidity among low-income women in Aleppo, Syria. Social science & medicine, 54(9), 1419-1427. DOI: 10.1016/S0277-9536(01)00123-X
Nevadomsky, J. (1991). Attitudes of Nigerian students toward marriage and family relationships. International Journal of Sociology of the Family, 21(2), 201–212. Retrieved$nbsp;from http://www.jstor.org/stable/23029820