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Analysis of Sales Promotion Effects on Household Purchase Behavior

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Table A7.1 ) are highly interrelated (0.80, 0.00, 156). Two measures <str<strong>on</strong>g>of</str<strong>on</strong>g> the size <str<strong>on</strong>g>of</str<strong>on</strong>g> the<br />

basket (BASKET1 and BASKET2, being number <str<strong>on</strong>g>of</str<strong>on</strong>g> different items purchased quarterly<br />

and number <str<strong>on</strong>g>of</str<strong>on</strong>g> different items purchased not <strong>on</strong> promoti<strong>on</strong> quarterly, see Table A7.1) also<br />

suffer from the interdependence problems (0.86, 0.00, 156). The tolerance values<br />

(Norusis 2000), the proporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> variability <str<strong>on</strong>g>of</str<strong>on</strong>g> a variable that is not explained by its linear<br />

relati<strong>on</strong>ship with the other independent variables, turns out to be 0.20 for the two basket<br />

size indicators and 0.35 for the two store loyalty indicators. These low tolerance values<br />

point at multicollinearity. It was therefore decided to incorporate the variables as factors.<br />

The two basket size measures served as input for a principal axis factor analysis, and so did<br />

the two store loyalty measures. The resulting factor scores are subsequently used as input<br />

for the binary logistic regressi<strong>on</strong> models (the factor scores are respectively named<br />

BASKET (basket size) and SHOPSHAR (share <str<strong>on</strong>g>of</str<strong>on</strong>g> the primary shop in total grocery<br />

expenditures)). When using these factor scores in the analysis, the potential<br />

multicollinearity problem is avoided (all tolerance values exceed 0.63).<br />

We remark that during the estimati<strong>on</strong> phase, some explanatory variable categories<br />

are combined because <str<strong>on</strong>g>of</str<strong>on</strong>g> a lack <str<strong>on</strong>g>of</str<strong>on</strong>g> observati<strong>on</strong>s. Adjacent categories, which obtained<br />

approximately the same estimates in the logistic regressi<strong>on</strong> analysis, are combined. The<br />

three highest Social class categories are combined. <strong>Household</strong> sizes exceeding 4 members<br />

combined into <strong>on</strong>e category (≥ 5). Some categories <str<strong>on</strong>g>of</str<strong>on</strong>g> type <str<strong>on</strong>g>of</str<strong>on</strong>g> residence are combined based<br />

<strong>on</strong> size <str<strong>on</strong>g>of</str<strong>on</strong>g> the house and signs <str<strong>on</strong>g>of</str<strong>on</strong>g> the estimated coefficients, leading to four categories<br />

(single family house, town house, apartment, and other). With respect to the employment<br />

situati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the shopping resp<strong>on</strong>sible pers<strong>on</strong> the two paid job pr<str<strong>on</strong>g>of</str<strong>on</strong>g>essi<strong>on</strong> categories are<br />

combined. Furthermore, the welfare, disabled, and pensi<strong>on</strong>ed categories are combined. The<br />

different categories <str<strong>on</strong>g>of</str<strong>on</strong>g> the job sector <str<strong>on</strong>g>of</str<strong>on</strong>g> the breadwinner are combined based <strong>on</strong> the level <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

employment.<br />

The binary logistic regressi<strong>on</strong> analysis is carried out for all six product categories<br />

together to identify general drivers <str<strong>on</strong>g>of</str<strong>on</strong>g> household promoti<strong>on</strong> resp<strong>on</strong>se. The results are<br />

discussed in the next secti<strong>on</strong>. The analyses are also carried out for each product category<br />

separately, to investigate the existence <str<strong>on</strong>g>of</str<strong>on</strong>g> a deal pr<strong>on</strong>eness trait (Secti<strong>on</strong> 7.6).<br />

124

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