There has always been a back-and-forth debate among scientists as to how much value should be placed in qualitative research. Qualitative research involves describing what is observed during an experiment. Being more subjective than quantitative research, it is often used during the early stages of a study to explore the problem at hand. There are advantages and disadvantages to qualitative research.
As an Exploratory Tool
When a researcher may not necessarily know what is going to happen during an experiment, she may make qualitative observations. This is useful because it will allow the experimenter to recognise what elements to focus on and measure during the study. In some ways, qualitative measurement shapes research. Because we can observe something happening, we know what to quantify and try to explain.
"Richness" of Data
Qualitative data is useful because it can provide a deeper and more complex understanding of what is going on in an experiment. It takes into account things like context, quality and meaning. For example, numbers can quantify factual data about a painting, but qualitative data can better describe how well done the piece is or how it makes people feel.
Hard to Reproduce
A disadvantage of qualitative data is that it is difficult for another person to interpret and reproduce the results. For example, a mixture can be turned "blue" by a chemical, but it is impossible to know if the exact shade of blue has been duplicated from a qualitative description. This type of measurement is not always as precise as quantitative data.
A major criticism of qualitative data is that it uses the researcher as the measuring tool, and a human for the most part will always have bias in his judgment. For example, one person might describe a brand of salsa as "hot," but another person may like spicy food and only classify it as "mild." Subjectivity prevents researchers from drawing the general conclusions that are needed to expand scientific knowledge, and it is one reason why qualitative measurement alone cannot hold up to scrutiny.