Chapter 8 Longitudinal Research
Longitudinal Research
Collection of data at different points in time
Inter-cohort Differences
Comparing different age cohorts at one point in time
Cross-sectional Research
Data collected from a representative sample at only one point in time
Longitudinal Research in Experiments
Delayed assessment is essential to measure the duration of impact of media effects
Trend Studies
Different people are asked the same question at different points in time
Period Effects
Influences associated with each particular time period
Cohort Effects
Influences associated with members in a certain birth cohort
Age Effects
Influences produced by growing older
Intra-cohort study
Reveal changes in a single cohort from one time to another
Follow-back panel
Selecting a cross-sectional sample in the present and using archival data to create the longitudinal dimension of the study
Catch-up Panel
Selecting a cross-sectional study done in the past and locating all possible units of analysis for observation in the present -lack enough identifying information to track down subjects -comparability of measures -limited to original variables measure
Cohort Analysis
The study of specific populations, usually all those born during a given period, as they change over time
Cohort
any group of individuals who are linked in some way or who have experienced the same significant life event within a given period
Cross-lagged Correlations
information about two variables is gathered from the same sample at two different times
Special Panel Designs
1. Retrospective panel 2. Follow-back panel 3. Catch-up panel
Causal Explanations
1. Ideographic 2. Nomothetic Different approaches have different priorities
Advantages and Disadvantages of Follow-back panel
+Changes that occurred over a long period of time can be analysed in a short period +Studying dwindling populations -Archives do not contain many variables that interest mass media researchers -May not represent all possible entities
Advantages and Disadvantages of Trend Studies
+Describe long-term changes in a population +Can be based on a comparison of survey data originally constructed for other purposes -Results are only as good as underlying data -Must be based on consistent measures
Advantages and Disadvantages of Cohort Analysis
+Highly flexible +Can be used with either original or secondary data -Specific effects of age, cohort and period are difficult to untangle through purely statistical analysis of a standard cohort table -Sample mortality
Longitudinal Research on the Internet
+Large number of individuals can be recruited +Find people from low-incidence groups -May not be representative -Sample mortality -Unable to verify identity of respondent
Advantages and Disadvantages of Combining Quantitative and Qualitative Data
+Qualitative helps in interpretation of quantitative +Suggest new hypotheses for future waves -Increase time and effort to analyse data
Advantages and Disadvantages of Panel Studies
+Useful to answer the dynamics of change +Repeated contacts reduce suspicions which may help yield more data than initial encounters +Allow for competing stimuli on the subject -Panel members are difficult to recruit -Sample mortality -Sensitisation Effect -Respondent error
Cohort Analysis Table Comparisons
1. Inter-cohort differences (down the column) 2. Trends at each age level (across a row) 3. Intra-cohort study (diagonal to the right)
Advanced Statistical Techniques
1. Path analysis 2. Log-linear models 3. LISREL (LInear Structural RELations)
Using Different Samples
-Bad science -Convert the data into z-scores to make it valid
Panel Studies
-Measuring the same sample at different points in time -Unlike trend studies, panel studies can reveal information about both net change and gross change in the dependent variable
Ideographic Explanation
-attempts to identify all influences -for specific entities (i.e. particular groups or individuals) and phenomena [particular]
Nomothetic Explanation
-identify a few causal factors -for many entities or phenomena (i.e. general trends) -probabilistic (uncertain and incomplete) -parsimonious (frugal, just enough)
Nomothetic Approach
-nomothetic: from ancient Greek nomothetikos, meaning "law" or "lawgiver" -predominant form of social science research -supported by law of diminishing returns
Cohort Analysis Table
-usually involves data from more than one cohort -interval between 2 periods of measurement corresponds to the age class intervals
Variation Effects
1. Age 2. Cohort 3. Period
Minimising Sample Mortality in Panel Studies
1. Cash incentive 2. Establish the credibility and value of the research project 3. Gather detailed information about the panel member (whereabouts, relationships) 4. Contact panel member between data collection waves 5. Give panel members a contact card to call if they change addresses
Types of Panel
1. Continuous 2. Interval Usage depends on purpose of the study
Conditions for Causality
1. Time order (cause precedes effect) 2. Association 3. Non-spurious (rule out alternative causes)
Types of Longitudinal Studies
1. Trend study 2. Cohort Analysis 3. Panel Study
Birth cohort
A group born within a year or time period
Interval Panel
Members agree to complete a certain number of measurement instruments only when the information is needed
Continuous Panel
Members who report regularly
Retrospective Panel Study
Respondent is asked to recall facts or attitudes from the past and these recalled factors are then compared with a later measure of the same variable, thus producing an instant longitudinal design Weigh the cost savings with possible losses in accuracy