One example of the longitudinal method being used in a study is Seven Up, shown on channel 4. It is a series of documentary films that have followed the lives of fourteen British children since 1964 from the age of seven. The children were selected to represent the range of socio-economic backgrounds in Britain at that moment in time; it assumed that each child’s social class predetermines their future. Every seven years new material is filmed from as many of the fourteen as possible and the last film was called ’49 up’, which was shown in September 2005. The purpose of the study is to examine how social class and up bringing may effect a persons future. This a very effective way of revealing extensive detail on the development process and allows the researcher to compare the participants, but it does assumes that social class in fact effects a persons future, which may be questionable. Each participant also brings their own genetic and ethnic background and experiences to the study, minimizing intra-individual variability. But this study also has its disadvantages, due to its amount of necessary resources and time consuming factors it is a very expensive method of research. What also happens in these and the cross-sectional studies is attrition, which is when a participant drops out of the study, either dying or refusing to participate, this is what happened in the Seven Up documentary. The researcher also has to wait a long period to get results and a great number of things may have influenced each participant’s development which may not be included in the study. The participants may also suffer from ‘practice effect’ which is when they begin to behave in a way they feel the researcher want them to, but many of these disadvantages may also occur in the cross-sectional methods.
In a cross-sectional study a researcher observes the differences between individuals of different ages at the same time. This generally requires fewer resources than a longitudinal method, and because the individuals come from different cohorts, the shared historical events are not so much of a confounding factor. Cross-sectional research may not be the most effective way of studying differences between participants, because these differences may result not from their different ages but from their exposure to different historical events. If we wanted to measure the current obesity levels in a population we would use the cross-sectional method, this is by selecting a random group of people. We could draw a sample of 1000 people randomly from a specific population, and then measure their weight and height. Then by calculating what percentage of the sample would be categorized as obese, we would be provided with a view of that population at that one point in time. But this would only give us that snapshot and not however tell us if obesity was decreasing or increasing, like a longitudinal study could. This method of research is less likely to suffer from attrition as it has a short time span and participants could also be replaced if it was in its early stages, due the its random sample group. It also does not require expensive or long- term resources, change of researcher and the results are almost immediately acquired. A mixture of both research methods involves observing individuals of different ages at the same time, and then records information on all participants over time. This is particularly useful because by comparing differences and similarities in development, it can be more easily determined what changes can be attributed to the individual or historical environments and which are truly widespread. This type of study would be even more resource consuming and expensive than the longitudinal study, but would give more accurate results.
The primary difference between cross-sectional and longitudinal studies is that cross-sectional studies take place at a single point in time and that a longitudinal study involves a number of measurements taken over a period of time. The cross-sectional research takes a sample of its target group and bases its overall finding on the views or behaviors of those targeted assuming it is typical of the whole group, as in the above example where the results can be generalized. Both of these methods are useful in carrying out developmental research but are somewhat opposites in terms of the costs, period of time, resources needed and the types of results they give. Therefore whichever of the two methods are chosen to conduct research would depend upon these and most importantly what exactly the researcher would like to find out.
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