Population and sample
The study covered all the six states in the southwestern geo-political zone of Nigeria.
Two schools were randomly selected from each of the three senatorial districts of each state.
Teachers were purposively selected to be all Mathematics teachers who were teaching Senior
Secondary School (SSS) level or who have taught these set of students at SSS level in time
past with the same textbook series in the selected schools. Thus, excluding other Mathematics
teachers who have not taught SSS with the series of the textbooks in their schools. A
purposive selection is desirable (Clifford, 1997) for it has enabled the researcher to choose
sample based on known characteristics. A total of 117 Mathematics teachers from the 36
schools formed the respondents. These were able to supply information on the textbooks
because of their long years of experience in using the textbooks, as the study revealed that
more than 80% of the teachers have been using the textbooks for more than 4years.