“A study on the percentage of adults who can read was conducted in 1950’s. A record has shown there was a big gap between man and women in education level. As the country developed, people mind set...

“A study on the percentage of adults who can read was conducted in 1950’s. A
record has shown there was a big gap between man and women in education level.
As the country developed, people mind set towards education has changed and the
ratio of population able to read was reobserved in late 1980’s. To improve the
ratio, education systems has been revised and new learning materials were
released. The effect of those measures were observed and recorded.”
From the above situation, explain the different between retrospective,
observational and design of experiment.