Short answer: quantitative research focuses on numbers, measurement, and statistical patterns. Qualitative research focuses on meaning, experience, interpretation, language, and context.
Quantitative research might ask how many people changed behaviour after an intervention, how strongly two variables are associated, or whether a treatment outperformed a control. Qualitative research might ask how people experienced the intervention, why they responded as they did, or what a policy means in daily life.
What each method does well
Quantitative methods are useful when researchers need measurement, comparison, prediction, or estimates of effect size. Surveys, experiments, administrative data, and statistical models can show patterns across many cases. The strength is scale and precision.
Qualitative methods are useful when researchers need depth. Interviews, ethnography, focus groups, document analysis, and case studies can reveal meanings and mechanisms that numbers alone may miss. The strength is context and interpretation.
Which is better?
Neither is automatically better. The right method depends on the question. If you want to know whether a drug reduces blood pressure on average, quantitative evidence is essential. If you want to know why patients stop taking it, qualitative evidence may be crucial.
Many strong research projects use mixed methods. Numbers can show that something is happening. Qualitative work can help explain how and why. Treating one approach as “real science” and the other as inferior is usually a sign that the question has not been understood properly.