What Is The Difference Between Qualitative Research And Quantitative Research?

Quantitative research (or testing) produces a numeric kind of answer to a problem (for example, 'there are 1000 colony forming units/g of E. Coli in this sample of milk powder';

Qualitative research produces a yes-no answer to a problem (for example, yes E. Coli is detected in the sample) but tells you nothing about the quantity.

Both these qualitative and the quantitative approaches to the research can be divergent, contrasting and complimentary. Both of these two types or researches seek to describe and explain phenomena, but have differing epistemological positions.   
  
An extensive and broad distinction can be made between the quantitative and the qualitative approaches to the research. The quantitative research always involves the collecting of the data in the form of numbers, which can be measured so it is measurable in nature. The qualitative research always involves the collection of data in the form of words and images and that is why it is interpretable. The qualitative research often involves the field observation, the intensive case studies, the narrative analysis, and the methods of constant comparison.

The quantitative research is simply based on the empirical evidence and aims to describe, explain and predict. The most significant and important difference between the qualitative and the quantitative research is the way in which each approach treats data and collects data. The type of the data generated in the course of conducting research depends very much on the method used to collect it. Therefore, it is necessary for a researcher to consider whether a qualitative or quantitative approach would be more appropriate whilst devising a research plan.

As a general definition, quantitative is numbers e.g. there was a two times increase in blah.
Qualitative is non numeric e.g. there was an increase in blah.

When you start to think about your research methodology, you need to think about the differences between qualitative and quantitative research.
Qualitative research explores attitudes, behaviour and experiences through such methods as interviews or focus groups. It attempts to get an in-depth opinion from participants. As it is attitudes, behaviour and experiences which are important, fewer people take part in the research, but the contact with these people tends to last a lot longer. Under the umbrella of qualitative research there are many different methodologies.
Quantitative research generates statistics through the use of large-scale survey research, using methods such as questionnaires or structured interviews. If a market researcher has stopped you on the streets, or you have filled in a questionnaire which has arrived through the post, this falls under the umbrella of quantitative research. This type of research reaches many more people, but the contact with those people is much quicker than it is in qualitative research.
Qualitative versus quantitative inquiry
Over the years there has been a large amount of complex discussion and argument surrounding the topic of research methodology and the theory of how inquiry should proceed. Much of this debate has centred on the issue of qualitative versus quantitative inquiry – which might be the best and which is more ‘scientific’. Different methodologies become popular at different social, political, historical and cultural times in our development, and, in my opinion, all methodologies have their specific strengths and weaknesses. These should be acknowledged and addressed by the researcher. Certainly, if you were to do so, it would help you to think about your research methodology in considerable depth.
Deciding which methodology is right for you
Don’t fall into the trap which many beginning (and experienced) researchers do in thinking that quantitative research is ‘better ’ than qualitative research. Neither is better than the other – they are just different and both have their strengths and weaknesses. What you will find, however, is that your instincts probably lean you towards one rather than the other. Listen to these instincts as you will find it more productive to conduct the type of research with which you will feel

Qualitative is to use your knowledge.

Quantitative is to question people like survey.