Introduction to biostatistics

Let’s say you want to figure out if people with high body mass index, or BMI, are at a higher risk of hypertension - or high blood pressure.

Let’s say that you decide to go out and find 100 people with hypertension and 100 people without hypertension and find out the BMI of each person in each group.

You might also collect other information about the individuals in each group, like how old they are, if they smoke cigarettes, or if they drink alcohol, since all of these factors can influence a person’s risk of hypertension.

All of these different pieces of information - called variables - can be put together into a single document or file, called a data set.

A data set usually includes independent variables which are thought to influence or change dependent variables.

In our example, the body mass index would be the independent variable and hypertension would be the dependent variable.

The process of collecting, organizing, and analyzing variables in a data set is called statistics, and when the data were collected from living things - like humans, aardvarks, algae, or bacteria - it’s called biostatistics, bio meaning life.

Now, there are two main types of biostatistics.

The first type is descriptive statistics, which is used to describe or summarize information about each individual variable in the data set.

Descriptive statistics can be used to find the mean - the average number calculated from a particular variable, the median - the middle number in a variable, and the mode - the number that occurs the most in the variable.

The descriptive statistics of each variable can be calculated for the whole sample - all 200 people - or in each group separately - the 100 people in the group with hypertension or the other 100 people in the group without hypertension.

For example, we might find that the mean body mass index of all people in the study is 24.5, or that the mean body mass index is 28 for the group with hypertension and 21 for the group without hypertension.

We can also use descriptive statistics to find the range, variance, or standard deviation, all of which are ways of understanding how the data are spread out or distributed for a given variable.

For example, we might find that the lowest measured body mass index in the group with hypertension is 23, and the highest is 33, so the range for body mass index in this group is 23 to 33.

Typically, descriptive statistics are reported in a graph or a table.

The second type of biostatistics is inferential, which is different from descriptive statistics in two ways.