How do you personalize ads?

Ads are personalized based on three factors

a) Demography based- This is usually a qualitative analysis. Based on distinct data sets, users are categorized into demographic segments e.g. 30-35 years of age, married, based out of midwest. Once this is done, each user is mapped into one of these demographic and its assumed that people within a demographic segment behave alike

b) Content based- This a classification process- It is beleived that categories of content go together e.g. While watching a family program, an ad that shows families shopping together will be well received

c) Contextual signals- This is based on certain characters, words on a screen at any given point of time. This will be used to predict the users preferences and thereby used to select an ad