Part Two: Design Issues: Evolution of Sample Survey Methodology
Sample Survey Designs obtain information by gathering responses to Survey Instruments by volunteers(Respondents) in some sort of Sample.
Care must be taken in both the Design and Administration of the Survey Instrument. Care must be taken in the selection of the Sample.
The current methodology allows for careful design of Survey Instruments, including review panels and pilot tests, in which the Survey Instrument is "tested" on a test(or pilot) group. The experience of the pilot group suggests editing and content changes to the Survey Instrument. The preferred method of obtaining Respondents is now Random Selection.
The integration of Psychology and Educational Research has led to an appreciation of the importance of the wording and delivery of Survey Instrument Items, as well as the need for Special Methods when dealing with extremely sensitive items.
The 1936 and 1948 Presidential Polls
A number of important survey failures stressed the need for Random Sampling. The Literary Digest US Presidential Poll of 1936 used a non-random sample targeting telephone directories, automobile registries and the LD subscriber list. Even though 2.4 million respondents were acquired for the poll, the poll failed miserably. Moreover, the bulk of US voters in the 1936 Presidential Election were neither automobile owners nor telephone owners nor LD subscribers.
Three major polling organizations - Crossley, Roper and Gallup, suffered poll failures for the 1948 US Presidential Election. All three organizations drew non-random samples which nicely resembled the population of US Voters, and all three polls still failed, though by a small margin. The problem was with the use of quota sampling.In quota sampling, poll workers are free to use judgment in selecting respondents, so long as the selected respondents meet quota requirements.
Gallup did two random-sample based polls for the 1936 US Presidential Election - both samples were much smaller than the 2.4 million LD Poll Sample. Gallupís 1936 polls correctly predicted both the results of the Literary Digest Poll and the Actual 1936 US Presidential Election Results. The bizarre thing is that the Gallup people did not use Random Sampling in the 1948 US Presidential Election Poll.
After the 1948 Presidential Poll failures, the importance of random sampling became clear.