So we build an additional column in the spreadsheet to hold X² and use the =LINEST(Y_values X_values 1 1) function. But Y=AX²+BX+C is just Y=AU+BV+C where U is X² and V is X. The LINEST function allows us to determine multiple regression coefficients, for example A, B, and C for the 2-variable model Y=AU+BV+C (U and V are the two variables). And let's assume that we want to determine A, B, and C in Y=AX²+BX+C. Using the data to determine the model is putting the cart before the horse.īut let's assume that you have a reason to believe that a quadratic or other polynomial is justified. ![]() So you must not fit a line or a quadratic to your data unless there is a theoretical basis for believing that the data obeys this model. JustKay wrote:do you mind going through how you got the polynomial trendline?This may be off topic, but in very general terms you must know the underlying model before it is justified to use the least squares method to fit a line or other equation to your data. You can select the green checkmark icon at the same time.Ģ01205162229.ods (9.9 KiB) Downloaded 821 times If this answered your question please go to your first post use the Edit button and add to the start of the title. I should point out that for your data, the R squared value is far from ☑ (about 0.11 for each of the first two tests), indicating that a straight line is a poor fit for it. If you want a single trendline for all of your tests, you'll need to copy your data as FJCC described before using the SLOPE, INTERCEPT, and RSQ functions. Of course if you do want to see the data charted, just select all of it (A1:J16) and use Insert > Chart > XY Scatter. The person who suggested creating charts and displaying the trendline equation may be unfamiliar with this simple method. I entered the three formulas in B18:B20, then filled those cells to the right (C18:J20). This is easily done if you want a trendline calculation for each test. ![]() ![]() Simply use the SLOPE, INTERCEPT, and RSQ functions as shown in my attachment. As you've probably discovered, this involves a lot of tedious clicking. JustKay wrote:The way I was told to do it with OpenOffice is by doing the scatter plot and then double click on the chart to put it in edit mode and then go to Insert -> Trend Lines to add the line, equation and R Squared to the chart.If you just need the slope, intercept, and R squared values, there's no need to create charts and fuss with adding trendlines.
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