You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Sampling Methods for Web and E-mail Surveys 
Chapter Title:  Unrestricted self-selected surveys 
1. Abstract of Cited Paper (BIB001):  This article provides a basic report about subject recruitment processes for Web-based surveys. Using data from our ongoing Internet Survey of American Opinion project, two different recruitment techniques (banner advertisement and subscription campaigns) are compared. This comparison, together with a typology of Web-based surveys, provides insight into the validity and generalizability of Internet survey data. The results from this analysis show that, although Internet survey respondents differ demographically from the American population, the relationships among variables are similar across recruitment methods and match those implied by substantive theory. Thus, our research documents the basic methodology of subject acquisition for Web-based surveys, which, as we argue in our conclusion, may soon become the survey interview mode of choice for social scientists.

Literature Review:
As with entertainment polls, unrestricted, selfselected surveys are surveys that are open to the public for anyone to participate in. They may simply be posted on a website so that anyone browsing through may choose to take the survey, or they may be promoted via website banners or other Internet-based advertisements, or they may be publicized in traditional print and broadcast media. Regardless of how they are promoted (or not), the key characteristics of these types of survey are that there are no restrictions on who can participate, and it is up to the individual to choose to participate (opt in). For example, BIB001 conducted a web-based survey 'to better understand the risks to adolescent girls online' by posting a link to their survey on the Seventeen Magazine Online website. Via the survey, the authors collected data on 10,800 respondents with 'identified behaviours that put them at risk'. The researchers were careful to appropriately qualify their results: The results highlighted in this paper are intended to explore the relevant issues and lay the groundwork for future research on youth in cyberspace. This is considered an exploratory study which introduces the issues and will need to be supplemented with ongoing research on specific characteristics of risk and prevention intervention. Furthermore, the generalizability of the study results to the larger population of adolescent girls needs to be considered. Due to anonymity of the respondents, one of the limitations of the research design is the possibility that the survey respondents did not represent the experience of all adolescent girls or that the responses were exaggerated or misrepresented. Unrestricted, self-selected surveys are a form of convenience sampling and, as such, the results cannot be generalized to a larger population. But as Berson et al. illustrate, that does not necessarily negate their usefulness for research. The web can also facilitate access to individuals who are difficult to reach either because they are hard to identify, locate, or perhaps exist in such small numbers that probability-based sampling would be unlikely to reach them in sufficient numbers. Coomber (1997) describes such a use of the web for fielding a survey to collect information from drug dealers about drug adulteration/dilution. By posting invitations to participate in a survey on various drugrelated discussion groups, Coomber collected data from 80 survey respondents (that he deemed reliable) located in 14 countries on four different continents. The sample was certainly not generalizable, but it also provided data that was unlikely to be collected in any other way, and which Coomber found consistent with other research. In addition, BIB002 proposed that these types of non-probability sample can be useful and appropriate for conducting experiments (say, in the design of web pages or web surveys) by randomly assigning members of the sample to control and experimental groups. In terms of psychology experiments,  states, 'For experimental research on the Internet, the advantage of yielding a heterogeneous sample seems persuasive considering that the most common criticism of psychological research is its over-reliance on college student samples.' THE SAGE HANDBOOK OF ONLINE RESEARCH METHODS