Measures of data
It is essential to be able to use and understand numerical data for carrying out fieldwork and in order to reach a conclusion. Handling data properly can show trends, patterns and can allow people to predict future trends.
Exploring the use of statistical techniques that help geographers analyse the data they deal with every day
They're all around us. They're on our food, in the news, in books and on social media. Andsometimes, this big jumble of numbers can seem daunting. But I think they're 100% interesting. Andif you know how to organise them really useful, too.
Take this set of numbers. The maximum daily temperature throughout the month of August.They're not doing much for me like this, but with some quick maths, I can get solid statistics鈥
like the mode, median and mean that allow me to interpret what is happening. Or with other data,like the UK population, you can calculate percentage increases and decreases over time.
It's clear that the population has gone up. But expressing the increase as a percentage is a far moreuseful number. That 0.4% annual population increase can then be instantly compared with othercountries.
Suddenly, we can really see which countries' populations are rising the fastest. By taking two piecesof data and looking for a relationship, or a correlation, we can examine trends and make predictions.Scatter graphs are great for doing this.
Here, you can see the size of population and life expectancy in the UK. There's clearly been acorrelation between the two and, as all the dots are forming a clear upward pattern from left toright, we can make a 'line of best fit'. This line should pass close to as many points as possible. And,using that line, we can make a prediction about the UK's population.
Scatter graphs can reveal strong positive, or upward, correlations. For example, the wider the river,the greater the velocity of flow. These graphs can also show strong negative, or downward,correlations.
Try this.
As the distance from the town centre increases, the volume of traffic decreases.
But take care.
Sometimes, a pattern seems to form and there is a line of best fit, but there is no correlation.Here, I've plotted foot length against average exam score. There's no cause or link between thesetwo factors, so any pattern here is just coincidence.
Being able to use statistics gives you a better sense of the world around you. You just need to knowwhat to do with them
Calculating percentage increase
Calculating percentage increase is an important skill for geographers to have.
When geographers collect data over a period of time, the results may increase. Calculating a percentage increase allows a geographer to see how much their data has changed.
For example, it may be useful to find out how much the width of a river channel increases as you travel downstream.
Method:
- Work out the The remainder left after subtracting one number from another. between the two numbers being compared.
- Divide the increase by the original number and multiply the answer by 100.
percentage increase = increase 梅 original number 脳 100
For example: the number of robins in a woodland area in February and March are counted. In February, 22 robins were counted. In March, 12 robins were counted. What is the percentage decrease of robins in the woodland?
The difference between the two numbers is 10.10 梅 22 脳 100 = 45.4
The percentage decrease of robins found in the woodland is: 45.4%
Calculating percentage decrease
Calculating percentage decrease is also an important skill for a geographer, as it allows a geographer to see how much their data has decreased over time or across locations.
For example, it may be useful to find out how much the The particles of rock carried by a river. particle size decreases in a river as you travel downstream.
Method:
- Work out the difference between the two numbers being compared.
- Divide the decrease by the original number and multiply the answer by 100.
percentage decrease = decrease 梅 original number 脳 100
For example: the number of robins in a woodland area are counted over two different months. In December, 15 robins were counted. In January, 23 robins were counted. What is the percentage increase of robins in the woodland?
The difference between the two numbers is 8.8 梅 15 脳 100 = 53.3
The percentage increase of robins found in the woodland is: 53.3%
Percentiles
Percentiles and quartiles are both ways of dividing data into smaller parts.
Whereas quartiles divide a set of data into 4 equal parts, percentiles divide the set of data into 100 equal parts.
Percentiles are commonly used to plot the growth of babies.
For example, a midwife weighs baby Anna and she is in the 90th percentile.
This means that if there were 100 babies (of the same age), 90% of them would weigh the same, or less than baby Anna, and 10% would weigh more.
Relationships
It is important to be able to identify relationships in data.
This allows trends to be recognised and may allow for predictions to be made. Relationships in data can be identified in several ways.
Scatter graphs
Scatter graphs show the relationship between two sets of data, eg number of tourists and number of tourist facilities or weight and height.
A line of best fit or trend line can be added to the scatter graph to show the relationship between the two variables. When drawing a line of best fit or trend line it is important to have as many points as possible going through the line.
A strong correlation is when the points on the scatter graph lie very close to the line of best fit. With a strong correlation, the two variables are related to one another - as one changes, so does the other.
A weak correlation is when the points lie far away from the line of best fit. In this case, the two variables are not necessarily related to one another - a change in one does not mean a change in the other.
A positive correlation is when an increase in one factor is mirrored by an increase in another (the line of best fit goes from the bottom left to the top right).
- For example, you are likely to get a positive correlation if you plot the GNP of a country against the proportion of households with a broadband connection. As one increases, the other will also generally increase as richer countries are likely to have better infrastructure.
A negative correlation is when an increase in one factor is mirrored by a decrease in another (the line of best fit goes from the top left to the bottom right).
- For example, you are likely to get a negative correlation if you plot the wealth of a country alongside infant mortality. As one increases, the other is likely to fall as richer countries tend to have lower rates of infant mortality as their healthcare systems are generally better.
An interpolate trend is when a value is found within the data set, using the line of best fit. The value was not originally plotted, but can be read off the line of best fit.
An extrapolate trend is when a value is found outside of the data set. Extrapolation may provide uncertain results as it is based on extending the line of best fit beyond a known set of data.