The number of contacts with the study population is a good way to define the types of study designs. On the basis of the number of contacts with the study population the study design can be classified into three types:
- Cross-sectional studies
- Longitudinal studies
- Before-and-after studies
Types of study designs
The cross-sectional study design
The cross-sectional study design is most commonly used in the social science research. The aim of these studies is to obtain information about a cross-section of a population. The information is collected once hence they are also called as one-shot studies. They are often used to know the prevalence of a phenomenon, situation, attitude or situation at the time of the study. No follow-up is done after the first contact with the study population neither it is required. These studies are therefore less time consuming and they can be conducted on a small budget. They are also simple in their design since the researcher decides about the problem that he wants to study. The next step is to locate the population and design a questionnaire or other survey design. The questionnaires are administered to the audience and information is collected.
Since these studies are conducted only once, therefore, they cannot measure change. The measurement of change in the situation or problem has great significance in the research. To know the change the researcher needs to contact the audience more than once for which he can use other study designs.
The before-and-after study design
The before-and-after study design as the name suggests is a type of study design in which the researcher contacts the audience twice. The reason is to collect the information from the audience before the administration of a program and then after the administration of the program to the audience. The researcher conducts the after study after the interval of sufficient time to let the program have its effects on the audience.
The main advantage of a before-and-after study is that it can measure the change in the attitudes of the audience before and after the administration of a program. As the researcher contacts the audience twice this study is expensive to undertake than a cross-sectional study, it is also time-consuming and requires more effort on part of the researcher.
The longitudinal study design
A longitudinal study can be defined as repetitive cross-sectional studies. The aim of the longitudinal study is to collect information from the respondents on a regular basis to know the pattern of change. The study population is contacted several times over a period of time, the length of the intervals can vary. The study population will remain same but the researcher can select a different sample each time from the same study population.
These studies are very useful in determining the pattern of change in a situation, phenomenon, problem or event. These studies, however, take a long time to complete and expense. These studies are also very useful in collecting factual information, govt and non-govt agencies conduct longitudinal studies on a continuous basis. These studies provide valuable information about the trends in population related to health, mortality, morbidity, labor, employment, immigration, education, and crime rates etc.
The disadvantage of the longitudinal study is that respondents often lose interest when they are contacted several times and they may provide answers to the questions without any thought. The researcher needs to use ways to motivate the respondents to be interested in the survey every time they are contacted. A mailed questionnaire may not be able to motivate the audience to be positive about the study, reaching the audience personally might help you develop a rapport with them. A personal contact with the audience can help you inform them about the importance of the survey and their participation.