Or perhaps they have a lack of access to medical facilities like trauma centers. But the reality is you would have to look at other factors like the possibility that doctors in rural areas might have less education or experience. In fact, that’s probably true and you could say it’s a simple fix: put more doctors into the population to increase life expectancy. For example, the following graph plots a single variable (number of doctors) against another variable (life-expectancy of women).įrom this graph it might appear there is a relationship between life-expectancy of women and the number of doctors in the population. Ordinary linear regression usually isn’t enough to take into account all of the real-life factors that have an effect on an outcome. When to Use Multiple Regression Analysis. You could set your X 1 as one type of sales, your X 2 as another type of sales and so on. But you might be interested in how different types of sales effect the regression. “sales”) against an independent variable (i.e. In one-variable linear regression, you would input one dependent variable (i.e. Multiple regression uses multiple “x” variables for each independent variable: (x1) 1, (x2) 1, (x3) 1, Y 1).Simple regression analysis uses a single x variable for each dependent “y” variable.The only difference between simple linear regression and multiple regression is in the number of predictors (“x” variables) used in the regression. Multiple regression analysis is almost the same as simple linear regression. It’s used to find trends in those sets of data. Multiple regression analysis is used to see if there is a statistically significant relationship between sets of variables. As you can probably see, 0.7 is a fairly decent model so you can be fairly confident in your weather prediction! The values range from 0 to 1, with 0 being a terrible model and 1 being a perfect model. This number tells you how good your model is. Regression also gives you an R squared value, which for this graph is 0.702. For example, how much snow will fall in 2017? Y = -2.2923(2005) + 4624.4 = 28.3385 inches, which is pretty close to the actual figure of 30 inches for that year.īest of all, you can use the equation to make predictions. What that means is you can plug in an x value (the year) and get a pretty good estimate of snowfall for any year. For 2015, it looks like the line will be somewhere between 5 and 10 inches! That might be “good enough”, but regression also gives you a useful equation, which for this chart is: You can see that the original guess (20 inches or so) was way off. Just by looking at the regression line running down through the data, you can fine tune your best guess a bit. There’s a whole host of tools that can run regression for you, including Excel, which I used here to help make sense of that snowfall data: That’s a good guess, but you could make a better guess, by using regression.Įssentially, regression is the “best guess” at using a set of data to make some kind of prediction. Looking at the following table you might guess somewhere around 10-20 inches. For example, global warming may be reducing average snowfall in your town and you are asked to predict how much snow you think will fall this year. In statistics, it’s hard to stare at a set of random numbers in a table and try to make any sense of it.