A study that provides longitudinal data on a group of people, households, employers, or other social unit, termed ‘the panel’, about which information is collected over a period of months, years, or decades. Two of the most common types of panel are age-cohorts, people within a common age-band, and groups with some other date-specific common experience, such as people graduating from university, having a first child, or migrating to another country in a given year or band of years. Another type is the nationally representative cross-sectional sample of households or employers that is interviewed at regular intervals over a period of years. Because data relate to the same social units, change is measured more reliably than in regular cross-sectional studies, and sample sizes can be correspondingly smaller (often under 500), while remaining nationally representative, as long as non-response and sample attrition are kept within bounds. These are the key problems for panel studies, as initial samples are eroded by deaths, migration, fatigue with the study, and other causes. Another problem is that people become experienced interviewees, leading to response bias. For example, they may report ‘no change’ since the previous interview, so as to avoid detailed questioning on changes that have in fact occurred.
Data are usually collected through interview surveys with respondents in the panel, with other informants (such as parents, doctors), with their spouses and other members of their household. With the respondent’s permission, data from administrative records may be added, such as information from educational or medical records, which are usually more precise than the respondent’s recollection. A panel element is sometimes added to regular cross-sectional surveys, and rotating sample designs are a hybrid between panel study and regular survey.
Advantages of Panel Studies
(a) If mini-samples of a given population are studied by single contacts and differences in the results noted from one period to another, one cannot know whether these differences are due to differences in the samples surveyed during each period includes the same persons or groups, as in the panel techniques, the variations or shifts in the results may be attributed with certitude to a real change in the phenomena studied.
For example, full effect of a campaign cannot be ascertained through sequence of polls taken on different people. They show only majority changes.
They conceal minor changes which tend to cancel out one another and sometimes even major changes if these are nullified by opposing trends. Most importantly, they neither indicate who is changing nor do they follow the vagaries of the individual voter along the path of his vote, to discover the relative effects of various other influential factors on his final voting verdict.
(b) Data secured from the same persons over a period of time, affording a detailed picture of the factors involved in bringing about shifts in opinions or attitudes, can be secured for everyone in the panel. An analysis of the chartered profile of individuals in a panel may afford the researcher an insight into the causal relationships.
(c) The information collected about each person from time to time tends to be deeper and more voluminous than that obtained in single contacts. It is possible, despite certain limitations to build up an inclusive case history of each panel member.
(d) Provided, of course, that the group constituting the panel is cooperative, it may well be possible to set up experimental situations which expose all members of the panel to a certain influence and thus enable the effectiveness of this influence to be measured.
(e) It has been the experience of researchers that the members of a panel learn to open out and unload their feeling in the course of frequentative interviews and so valuable comments and elaboration of points made by them can be secured.
Whereas the first interview may elicit only ‘yes’ or ‘no’ responses from the respondents, the repeated interviews or measurements spread over a continuum of time may elicit from them elaborate responses in so far as they might have thought deeply about the problem after the first administration. On first contact, the informants may be suspicious of the investigator and may have little familiarity with the problem.
Limitations of the Panel Studies
The problems raised by the panel procedure are often sufficient to off-set the gains attendant upon it. We may briefly discuss the Limitations of the Panel techniques.
(a) The loss of panel members presents a formidable problem for the researcher. People change their locale, become ill, or die or are subjected to other influences which make it necessary for them to drop out of the panel. Thus, the panel that was initially intended as a representative sample of the population may subsequently become unrepresentative.
The losses in the membership of the panel may be occasioned by the loss of interest among the panel members or a change in attitude toward the panel idea. Not infrequently, the enthusiasm of the panel members dies down after the first or the second interview.
(b) Paul Lazarsfeld has pointed out that the members of a panel develop a ‘critical set’ and hence cease to be representatives of the general public. The panel invariably has an educational effect.
It tends to dramatize and increase one’s interest in otherwise unobserved elements and to heighten one’s interest in otherwise unobserved elements and to heighten one’s awareness of things and events around him. Hence the mere fact of participation in the panel may change a person’s attitude and opinions.
(c) Once the members of a panel have expressed an attitude or opinion they tend to try to be consistent and stick to it. Thus, panel members as compared to the general public are less likely to change. Thus, the panel may misrepresent the population.
(d) The detailed records are available for the most stationary elements of the population. Of course, the mobile groups of a community belong to the panel for a shorter time. Panels composed of the same persons for many years will gradually become panels of old people and eventually die out.
A panel study, however, is not always feasible. One of the difficulties is that the events or thoughts may already be long past by the time the researcher begins. Occasionally, memory is not always reliable and the respondents may be inclined to ‘construct’ these part events not so much from their fading memories but from their personalized theory about their past.