Quantitative research applies scientific methods to investigate the empirical relationships between different phenomena. It studies numerical data in a formal, systemic and objective manner to understand such relationships. The objective is to determine the relationship between an independent variable and a dependent/outcome variable. Measurement is important in turning empirical observations into mathematical expressions. Mathematical theories, hypotheses and models are then used to explain the outcome. Quantitative research questions are designed to quantify relationships between variables like height, volume, speed and time. The design of the questions is very objective. The questions are designed to be deductive hence tend to test a given theory. They produce results that can be generalized. The results are in the form of numbers or data that can be easily converted into numbers.
Quantitative research studies can be broadly classified as descriptive or experimental (Hopkins, 2000). There can also be categorization as quasi-experimental and causal studies. Descriptive questions can only reveal associations between variables while experimental studies go on to establish causality. Descriptive questions usually test the subject once. Their aim is to highlight the natur of relationship between two different variables. They are observational in nature and the person conducting the experiment does not interfere with the subject. The simplest form of a descriptive study is the case study. Here the questions are aimed at generating data on only one subject. Descriptive questions capturing several cases constitute a case series. Quantitative research questions are also used to study several variables of interest in a sample of subjects once to determine the relationships between them in cross-sectional studies.
Another form of descriptive studies is the case-control study. Here the quantitative research questions are designed to compare cases (subjects with a particular attribute, such as lung disease) with controls (subjects without that attribute). Comparisons are then made concerning exposure to a suspected causative agent, for example in this case- cigarette smoke. Such studies aim to determine situations in the past that may be responsible for making the subjects to become cases instead of controls. This is why they are also known as retrospective studies.
Quantitative research questions used in experimental studies are designed to produce a continuous flow of data during the research period. Such studies employ repeated meassures and involve more than just observation of the subject. The researcher manipulates the subjects in particular ways and records the changes in the variables to be studied. The researcher can introduce several control aspects into the experiment and also allocate the subjects to different experimental groups in a random manner (Hopkins, 2000). The simplest form is the time series, where measurements are taken repeatedly before and after manipulation on one or several subjects. The best results are seen in the randomized control test in which the quantitative research questions are designed in such a way that the subjects do not know which experimental group they belong to and thus cannot manipulate the result. Such a model will also protect against the researcher being compromised into prejudiced interpretation.
Quantitative research questions ought to be designed while taking into consideration the ethical issues that may arise. Furthermore they should facilitate cooperation from the subjects. The questions will determine the quality of the results obtained and therefore should be precise but thorough. The researcher should design the questions in such a way that he/she does not pre-empt a certain outcome. The questions should also eliminate problems that may arise such as confounding results.