Regression and Prediction Equations in SPSS with Dr. Ami Gates

hey everybody this is part two to our unit three and four how-to videos and in this particular video we're going to look at using SPSS to create a prediction equation using two variables that have a high enough or strong enough correlation and so let me explain a little bit about what we're doing and why we're doing this sometimes we think that variables have a high correlation meaning that they they can affect not necessarily affect each other but if one of them is high you can maybe expect the other one to be high and if one of them is low you can expect the other one to be low if they have a strong positive correlation for example if I think that a student's previous GPA is highly correlated with their final exam score then I could even take that information and I could produce a prediction equation and that prediction equation could allow me to plug in a student's previous GPA and calculate their final exam score or what I predict their final exam score might be now remember these prediction equations are based on correlation so they're never a hundred percent they're not always accurate and they're not always right they're just there to give you an idea of based on the regression analysis that we're going to do and based on the fact that previous GPA and final exam score have a high enough correlation we can use the prediction equation to get an idea of what we think a final exam score might be based on a student's previous GPA so that's basically what we're doing here now our first step whenever we want to create a prediction equation is always going to be to make sure that the correlation between the two variables that we're looking at is high enough so let's do that first I'm going to use SPSS to calculate the correlation between previous GPA and final exam points I'm gonna click analyze correlate and bivariate because I have two variables now you can see we've done this a couple times but let's put these back this is how it looks when we begin and we want to find the correlation between final exam points and previous GPA so we'll move both of these over we'll make sure that the Pearson which is our Pearson R value or Pearson correlation is checked and we'll click OK now when we do this we see that SPSS gives us our correlation results the correlation between final exam points and previous GPA is 0.49 eight point four nine eight now that's nearly 0.5 and it's a strong enough positive correlation for me to feel comfortable creating a prediction equation where I want to use a student's previous GPA to try to predict or guesstimate what their final exam points are going to be so how do I do that okay to do that or to create a prediction equation I need the numbers that meet that have to go into that equation those numbers are often called coefficients now the good news is that SPSS will generate those coefficients or prediction equation numbers for me I just have to tell it what I want so I click on analyze and then I choose regression and then linear so in order to create a prediction equation I'm going to use linear regression to get the numbers that are going to go into my prediction equation so I'll choose that option and let's go ahead and put everything back and what I need to do first is I need to tell SPSS which one of my two variables is the independent variable and which one of my two variables is the dependent variable now whenever you have to answer this question you need to think it over you need to think to yourself okay well what are my two variables and what am I trying to predict in this case previous GPA is one of my variables and I want to use previous GPA to predict final exam points because I'm predicting final exam points that's my dependent variable so final exam points are what I'm predicting is going to depend on the students previous GPA so previous GPA is my independent variable final exam points is my dependent variable in this case and again you always have to think this through logically and make sure that you're making the right choice then I'm going to click OK in this case SPSS is going to generate a lot of outputs here they all are but the one that I'm looking for specifically is called coefficients that's what I'm looking for here because I want to create an equation that uses previous GPA to predict my dependent variable of final exam points these are the two numbers that I want to grab the five point one eight zero is one of the numbers I need for my prediction equation and the forty seven point zero eight three is the other number I need for my prediction equation now here's what the prediction equation is going to look like using those two numbers and remember those two numbers were five point one eight zero that was the one next to my previous GPA and the other one was forty seven point zero eight three that was my constant value so my prediction equation literally looks like y equals the first number here which is my five point one eight zero multiplied times X add it on to the constant value that I'm given let's see those two numbers again let's make sure we can see where those came from remember one of them was forty seven point zero eight three the other was five point one eight zero notice that the five point one eight zero is multiplied by my X or independent variable which is my previous GPA SPSS actually tells you this it says look your previous GPA is your independent variable or your X in your equation here's the value you multiply next to that X and that's exactly what I've done here then SPSS tells you the constant that you want to add on in your equation is right next to the word constant my forty 7.0 eight three so to build my entire equation I use both of these values from SPSS so what's actually going on here is why is my dependent variable and in this case that's final exam points X is my independent variable in this case previous GPA my prediction equation uses the values from SPSS and the value next to previous GPA which is my independent variable gets multiplied by X now how do I use this prediction equation well if I know that a student has a previous GPA of 3.5 I can plug in that value of 3.5 into my prediction equation multiply it by five point one eight zero add on the forty seven point O eight three gives me the predicted final exam points of 65 point 21 that's the predicted final exam points that I expect to get from a student who has a previous GPA of 3.5 so that's how we use SPSS to generate a prediction equation and that's all there is to it thank you very much for joining me for this how-to video and I'll see you all in class

Channel: ProfessorAmiGates

Views: 93,030

Rating: 4.9124727 out of 5

Keywords: SPSS, graph, graphing, Dr. Ami Gates, statistics, prediction, regression, linear, descriptive

Id: LyVP00IS5lM

Length: 9min 25sec (565 seconds)

Published: Fri May 04 2012