Cohort Analysis, trend studies, and panel studies

COHORT ANALYSIS

Cohort was one of the ten divisions of military legion to the Rome .For research purpose a cohort is any group of individuals who are linked some way or who have experienced the same "significant event" in a given period. In usually, the significant life evens is birth control in which case the group is turned of birth control. There are however many other kind of cohort, including marriage, for example all married between 1990_1995, divorced; all those divorced between 1995_2003 educational (class of 1990).

"Any study in which there are measures of characteristics of one or more cohorts at two or more points in time is a cohort analysis"

Cohort analysis attempts to identify a cohort effect: "Are changes are the department variable due to aging, or are they present because the sample members belong to the same cohort?"

Typically, a cohort analysis involve data in more than one cohort and a standard table of presenting the data from multiple co its was proposed by "Glenn"

Cohort analysis is an appealing and useful technique because it is highly flexible. It provides insight into the effects of maturation and social, cultural, and political changes. In addition, it can be used with either original data or secondary data. In many instances, a cohort analysis can be less expensive than experiment or surveys.

o        EXAMPLE:

Cohort analysis is widely used in advertising and marketing research. Rentz et al (i 983) conducted a cohort analysis of consumers born in four time periods 1931 1940, 1941_1950, 1951-1960, 1961_1970. Soft drink consumption was dependent variable.

Cohort analysis is also useful in studies of public opinion. Wood (1986) outlined the use of cohort analysis in marketing and showed how time examined cohort data to chat trends in its subscriber ship.

Rosengren and Windahl (1989) used cohort analysis as part of their in-depth longitudinal study of T.V. usage by Swedish youngsters.

PANEL STUDIES

The measurement of the same sample of respondent at different points in time represents the panel design. Unlike `trend studies'  'panel studies can reveal information about both net carriages and gross change in the dependent variable.

A study of voting intentions might reveal that between Time 1 and. Time 2, 20% of the panel switched from Candidate A to Candidate Band 20% switched from Candidate B to Candidate A. Whereas a trend study would show only a net change of zero , the panel study would show high degree of volatility in voting intention as the gross changes simply canceled each other.

Similarly to Trend and Cohort Studies, Panel Studies can make use of mail questionnaire, telephone interviews or personal interviews. Television networks, advertising agencies and marketing research firms use panel studies to track changes in shift of consumers' behavior.

Panel studies can reveal shining attitude and patterns of behavior that might go unnoticed with other research approaches; thus trend, new ideas, fads, and buying habits are among the variables investigated. For panel studies on the effectiveness of political commercials. For example, all members of the panel would be interviewed periodically during a campaign to determine whether and when each respondent makes a voting decision. Depending on the purpose of the study, researcher can use either a "continuous panel" with regular member or "Interval panel" with members voting on demand. Panel data is particularly useful in answering questions about the dynamics of change.

o        EXAMPLE:

Most famous example of panel studies technique in mass is the collection of national television audience data by the A.C. Nielsen Company. Neilsen's sample contains of approximately 4,000 households located across the United States. Other panel is maintained by such commercial research organization as Market Fact Inc. ; National Family Opinion Inc. and the Home Testing Institute.

TREND STUDIES:

The `Trend Studies' studies different group of people at different times for the same population. The trend studies are popularly the most common longitudinal study in mass media research. Trend studies are common around election times. Trend studies provide information about term changes at an aggregate level. They are valuable in describing long-term changes in a population. They can establish a pattern over time to detect shifts and changes in some events. Broadcast researchers ,for example, compile trend studies that chart fluctuation in viewing levels to the three major networks.

They can be based on a comparison of survey data originally constructed for other purpose. Hyman (1987) provided extensive guidance on the secondary analysis of survey data.

The growing movement to preserve data archives and the ability of micro-computer networks that make retrieval and sharing much easier suggest that this technique will gain in popularity. Secondary analysis saves time, money and personal; it also makes it possible to understand long-term changes.

Trend analysis is only as good as underlying data. If data are un reliable, then false trends will show up in the results.

o        EXAMPLE:

Both university and commercial research firms have asked some of the same questions for many years for national and statewide trend studies. For example, in the United States, a question about satisfaction with the President's performance has been asked hundred of times.

Public Opinion Quarterly has a regular section entitled "The Polls" that allows researchers to construct trend data on selected topics. The following trend data have appeared

1.                    A 16 year sampling of attitude about the Soviet Union.

2.                    A 15 year trend about attitude towards environmental issues.

A 5 year compilation of Israeli attitude towards security.