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Gender Diversity on the Board - BI Norwegian Business School

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GRA 19001 Master Thesis<br />

5 Statistical tests<br />

5.1 Base-case model<br />

Our data set c<strong>on</strong>tains repeated observati<strong>on</strong>s of <strong>the</strong> same firm for up to eight years. We<br />

use <strong>the</strong> fixed effects model to handle this panel data setting. Fixed effects allow us to<br />

c<strong>on</strong>trol for unobserved explanatory variables and to analyze change over time. The more<br />

time points a firm is observed, <strong>the</strong> more informati<strong>on</strong> <strong>the</strong> firm provides. Hence, we <strong>on</strong>ly<br />

study firms that are present for at least three years to ensure that sufficient informati<strong>on</strong> is<br />

provided. The first step in <strong>the</strong> fixed effect model is to compute <strong>the</strong> mean for each<br />

company, for each variable, and subtract this mean from all observati<strong>on</strong>s. For variables<br />

that stay c<strong>on</strong>stant over time, <strong>the</strong> value in each year equals <strong>the</strong> average value across years.<br />

Hence, it cancels in <strong>the</strong> regressi<strong>on</strong> equati<strong>on</strong>. When means are subtracted, we estimate <strong>the</strong><br />

model using ordinary least-squares (OLS). (Petersen, 2004)<br />

Table 5.1 shows results from OLS when estimating <strong>the</strong> base-case model by <strong>the</strong> fixed<br />

effects approach as described above. To c<strong>on</strong>trol for o<strong>the</strong>r firm characteristics that can<br />

influence <strong>the</strong> dependent variable we c<strong>on</strong>trol for firm size and firm age in <strong>the</strong> regressi<strong>on</strong>.<br />

The base-case model will be presented for large n<strong>on</strong>listed firms as well as all n<strong>on</strong>listed<br />

firms. We limit <strong>the</strong> attenti<strong>on</strong> to individual coefficients with a p-value of 10% or less.<br />

22

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