Bias occurs when the researcher unintentionally influences the study findings in some way. For example, a study participant may say only what they think the researcher wants to hear, not what they really believe. Or, during data analysis, the researcher may leave out information if those findings contradict the researcher's view of the issue. Bias can occur during study design, data collection and data analysis.
One of the major goals of research is to generalize the study findings to a broad group or population. In order for this to be possible, it is necessary that participants enrolled in the study are representative of the broader population being studied. Because qualitative research does not involve random sampling from the population to recruit research participants, it is challenging to get a sample group that is representative of the population. As a result, qualitative researchers have to be careful about making broad conclusions from their research.
Compared to quantitative research, it is more difficult to determine the validity and reliability of qualitative data. It does not mean that the data are less valid, but that it is more difficult to measure their validity. Also, qualitative studies are difficult to replicate, an important test of the strength of the findings. The skills of the researcher significantly determine the strength of qualitative research findings.
Both data collection and analysis can pose logistical challenges to qualitative research teams. Qualitative research techniques such as ethnography and interviewing are time consuming and demand a lot of person power. Successful qualitative research relies on high levels of trust between the research team and study participants, which also takes some time to develop. A main characteristic of qualitative research is that interview questions are open ended, creating considerable work during the analysis phase. Because of these logistical challenges, qualitative studies usually involve fewer participants than quantitative research.