Answers are:
1) religious views: some religious systems encourage the vision of the world and some specific matters, prohibited , tabu, or they arent given any importance as in other beliefs, therefore any people not conscious about them will be biased. (for example research of sexuality,gender identity and behavioral patterns among others)..
2) political views are often a characteristic issue when adressing issues in social sciences , ethics, since they are portrayed as ideology they often tend to exclude the contending ideologies, in so they pose a problem for research in a way that the bias is not always recognized as such.
4) upbringing: The information presented in textbooks is often the issue of debate, sometimes this occurs when also another of the factors, is present, for example the theory of evolution is not accepted in Christian education, therefore it generates a bias and attitude of ignorace towards other subjects that can also include historical events.
3) the country lived in, is another instance , where cultural factors are to be taken into account . In some countries people lack cosmopolitan views or they even have restrictions on accesing certain kinds of information.