1.3 Benefits of the body mass index
Quantitative research is particularly useful for studying whole populations and identifying general trends and relationships because it makes use of statistical data. The results of large-scale, quantitative studies are frequently summarised in documents like government-commissioned reports or academic journal articles, but these documents are not particularly accessible or easy to interpret. For this reason, agencies such as Public Health England (disbanded in 2021, partly incorporated into the Office for Health Improvement and Disparities) sum up key findings using infographics, as seen in Figure 4 – although these too can be inaccessible to some.
Body mass index (BMI) is a widely used measure for working out if a person’s weight is ‘healthy’. BMI is calculated by dividing an adult’s weight in kilograms by their height in metres squared. As such, BMI can be used to calculate and compare weights of groups of people relative to their heights. The weight categories for interpreting BMI for adults are shown in Table 1.
Table 1 Weight categories for BMI (NHS, 2023)
| Weight category | BMI |
|---|---|
| Underweight | <18.5 kg/m2 |
| Healthy weight range | 18.5–24.9 kg/m2 |
| Overweight | 25–29.9 kg/m2 |
| Obese | 30–39.9 kg/m2 |
| Severely obese | >40 kg/m2 |
However, BMI has its critics, and you will look at some of the drawbacks of this statistical method next.
OpenLearn - Healthy living and choice (title tbc)
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