Notes on Data Collection and Analysis Dale Weber PLTW EDD Fall 2009

Things to Consider Experiment Planning Replication Randomization Blocking Data Analysis Strength of “Effects” – Individual Factors – Factor/Factor Interaction Modeling Linear Regression

Replication 1.Using mean of replicate data gives more precise results 2.Comparing mean to raw data gives an estimate of experimental error – Standard Deviation of data is commonly used – Also, can identify Outliers Typically 3 Replicates are considered sufficent

Equal Means 2x Variance Outliers 2 close pts - suggests dropping outliers - performing another experiment

Randomization and Blocking Want to “average out” the impact of extraneous factors Ex. Weather, pressure variation, cone smoothness, etc. Compile a list of all experiments to be performed (including replicates) Perform tests in random order Roll dice or use computer (Excel –RAND) to generate random sequence

Strength of Effects Montgomery, D.C. Design and Analysis of Experiments, Effect of A: Average of High A value minus Average of Low A value

Factor/Factor Interaction Montgomery, D.C. Design and Analysis of Experiments, Effect of A at Low B: = 30 Effect of A at High B: 12 – 40 = -28 Another way to view it Since the Effect of A depends on value of B: There is Interaction

Modeling Regression Model Measured output Random Noise Coefficients Mean Factor Values Interaction Term Can add other terms to model:and so on.

(Multiple) Linear Regression You know Linear Regression from using adding trend-lines to plots in Excel For multiple independent variables, need to use LINEST function in spreadsheet 1.Make table of model terms in columns with output in last column:

(Multiple) Linear Regression (2) 2.Enter LINEST Command in blank cell Measured Data Model Input Data (Exp Factor values and combos) Force const (    to 0? T = No F = Yes Calculate Fit Statistics Least Squares Fit Coefficients  ’s – in reverse order! R 2 – value (Goodness of Fit)

(Multiple) Linear Regression (3) 3.Drag LINEST cell and Fill i.Drag box needs as many Columns as factors and factor combos in the model + 1 ii.Drag box needs 5 Rows. 4.Press F2 to convert LINEST formula and Drag box to an array. 5.Press CTRL+SHIFT+ENTER to fill

(Multiple) Linear Regression (4) 6.Use Least Squares Model to make predictions Note: 1. There is no noise term in the fit model 2. A hat (^) signifies model estimate ANY QUESTONS? Don’t Forget: - LINEST Help File Handout - Montgomery Handout