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Analysis of Sales Promotion Effects on Household Purchase Behavior

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make n purchase decisi<strong>on</strong>s. But those purchase decisi<strong>on</strong>s probably depend <strong>on</strong> each other.<br />

Indeed, that is why the explanatory variables X other and X *other are added to the multiplied<br />

records. We expect that the informati<strong>on</strong> provided by those two additi<strong>on</strong>al variables is<br />

sufficient to remove most <str<strong>on</strong>g>of</str<strong>on</strong>g> the bias. This will be validated in Secti<strong>on</strong> 7.5.1 by comparing<br />

the results obtained using <strong>on</strong>ly the single-promoti<strong>on</strong> data with the results obtained from the<br />

combined record data.<br />

Why should we even bother about the multiple-promoti<strong>on</strong> data at all? Why not<br />

<strong>on</strong>ly take the single-promoti<strong>on</strong> data into account? This research is aimed at acquiring<br />

knowledge about the drivers <str<strong>on</strong>g>of</str<strong>on</strong>g> sales promoti<strong>on</strong> resp<strong>on</strong>se. If we would <strong>on</strong>ly take singlepromoti<strong>on</strong><br />

data into account, we would not obtain insights in the impact <str<strong>on</strong>g>of</str<strong>on</strong>g> the presence <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

other types <str<strong>on</strong>g>of</str<strong>on</strong>g> promoti<strong>on</strong>s <strong>on</strong> sales promoti<strong>on</strong> resp<strong>on</strong>se. This could lead to an unrealistic<br />

descripti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the drivers <str<strong>on</strong>g>of</str<strong>on</strong>g> sales promoti<strong>on</strong> resp<strong>on</strong>se. The presence <str<strong>on</strong>g>of</str<strong>on</strong>g> other types <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

promoti<strong>on</strong>s for other SKU’s within the same category will intuitively have a detrimental<br />

effect <strong>on</strong> the impact <str<strong>on</strong>g>of</str<strong>on</strong>g> a promoti<strong>on</strong>. Before presenting the results <str<strong>on</strong>g>of</str<strong>on</strong>g> the data validity check<br />

and the results <str<strong>on</strong>g>of</str<strong>on</strong>g> the empirical hypotheses testing, variable screening is performed to<br />

circumvent possible multicollinearity problems.<br />

7.4 Variable Screening<br />

All variables that could possibly be related to promoti<strong>on</strong> resp<strong>on</strong>se (Table A7.1) are<br />

candidates to be incorporated in the binary logistic regressi<strong>on</strong> analysis. But, the presence <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

multicollinearity could lead to large standard errors, which in turn could lead to unjustified<br />

n<strong>on</strong>-significance <str<strong>on</strong>g>of</str<strong>on</strong>g> possible drivers <str<strong>on</strong>g>of</str<strong>on</strong>g> promoti<strong>on</strong> resp<strong>on</strong>se. In this secti<strong>on</strong> we discuss<br />

which variables are excluded from the analysis and for what reas<strong>on</strong>. If a correlati<strong>on</strong><br />

coefficient is provided in the text, we will also menti<strong>on</strong> its 2-sided significance (p-value),<br />

and the number <str<strong>on</strong>g>of</str<strong>on</strong>g> observati<strong>on</strong>s it is based <strong>on</strong>. These three numbers will be put between<br />

parentheses. For example (0.65, 0.03, 156) indicates that, based <strong>on</strong> 156 observati<strong>on</strong>s, a<br />

correlati<strong>on</strong> coefficient <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.65 was found and that the associated p-value is 0.03. This pvalue<br />

<str<strong>on</strong>g>of</str<strong>on</strong>g> less then 0.05 implies that the correlati<strong>on</strong> coefficient found statistically differs<br />

significant from zero (two-sided) using a significance level <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.05.<br />

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