*(From the archives July 1997)*

I finally came up with the solution. As we looked at the numbers on the paper reports for headcounts, I recognized that none of the numbers were tying. Every cell contained a possible double count depending on the rollup. Only zero level numbers were reasonable. I reasoned that at every level of aggregation, what we wanted was a yes or no by individual.

**Binary Aggregation**

The solution is to create a member formula for Heads which performs the equivalent of a binary aggregation at every level of aggregation of every dimensions but the top level of the Individual dimension.

In order to get unique heads as a measure do the following.

First, you **must **have a
dimension for individuals and input records by individual.

Input a dummy measures field called Hits by adding a "1"
as a column in your input file by modifying your load rule.

Individual | Dim X | Dim Y | Hits |

A | 1 | 0 | 1 |

A | 1 | 1 | 1 |

A | 1 | 0 | 1 |

A | 0 | 1 | 1 |

B | 1 | 0 | 1 |

B | 0 | 0 | 1 |

Notice that if you query Hits for XY = {1,0} you will get 3
despite the fact that there are only 2 distinct individuals. (A hits twice),
Unless you break out the individual dimension, you can't know that A hit twice.

The solution is to aggregate Hits at the descendants of the
Individual dimension according to the following logic:

hits = (if <>#missing) 1, #missing

At this point you can export the database and get rid of the
Individual dimension, if you like.

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