Quantitative research is concerned with measurement of a market, including the calculation of market size, the size of market segments, brand shares, purchase frequencies, awareness of brands, distribution levels, and so on.
This quantitative data is required at varying levels of accuracy and the methods used must be capable of achieving this.
Qualitative information is harder to define but the emphasis is on 'understanding' rather than simple measurement. For example, quantitative research may tell you that Advert A is recalled more often than than Advert B, but how does A work as an advert and why is it more effective than B? This is when qualitative research is needed.
Much qualitative research is concerned with empathizing with the customer and establishing the meanings he or she attaches to products, brands and other marketing objects. Another focus is motivation. For example, why does one product meet customer needs over another - and what are these needs that are being met?
Qualitative research is conducted amongst a smaller sample compared to quantitative research. In the case of attitudes to brands, for example, qualitative research may determine a specific view held about the brand, whereas quantitative research would tell us what proportion holds that view.
Quantitative and qualitative research work in tandem. The qualitative element frequently takes place at the front end of the study, exploring values that need measuring in the subsequent quantitative phase.
Qualitative research may offer a diagnostic understanding of what is wrong, while the quantitative research provides hard data across different respondent groups that can lead to specific recommendations with measures that can be used as controls to determine the effectiveness of actions.