Developmental Longitudinal  and Cross Sectional Survey:

Suppose, you wish  to  study the  growth and development pattern  of children from birth  tofive years  of age. This  is an example of development  research. This studycan be  done in  two ways. One, the researcher can  follow a group of new born  infants from  their birth  to five years of age to assess aspects of their growth and development patterns. This  is called  as  longitudinal survey. The second method  is  a cross sectional  survey where the researcher for example takes  representative samples fiom  the  age groups of birth-three months, four-six months, seven, nine months,  and so on  till the  sixteenth month. Both methods have  certain advantages and disadvantages. Let  us examine them. 

In  longitudinal  survey  sequence of events  is  observed  in  each subject selected  for  the  study. Data  here  is more  objective as the  subjects do not have  to  recall  for reply. The most  difficult part of  this study is to keep contact with the subjects as  the individuals may move  out of the place  of residence or  drop out of  the study. This is called  as  the  subject mortality. For this reason a large number  of subjects is needed  for  desired  sample size in the  end  of the study. It takes a  long  time  to know  the final results. Many  a  time  cross-sectional  study is done  in  place  of  longitudinal study. Advantages  are  that  it  can  be  completed  in a relatively short time and  is  relatively less expensive; sample loss  is  less  than  longitudinal study;  and  the results are  known early. The disadvantage. is that  the method  can  only  consider the present and  past and  not the  future as  in longitudinal study. So, trends and  patterns over  a  period  of  time  can  not be  described. 

The case study and  retrospective survey (or ex-post  facto) are  two other methods which are sometimes included  as  types oi survey method or sometimes are  treated separately. However, we  are discussing them under survey.