turn on suggestions

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

Find a Community

- Home
- /
- Analytics
- /
- Data Mining
- /
- How to choose the Best Reference Group? Please Hel...

Topic Options

- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Highlight
- Email to a Friend
- Report Inappropriate Content

11-15-2013 09:58 AM

Hi All,

Below is my Logistic Regression output results. I had a question, how to choose a group of reference? Does our choice of group of reference improve the model? For example in my case below, VAR1 has a negative Estimate, which means that customers in group(1,2,5,9,11,.) are less likely to respond. My group reference is the group that is more likely to respond. Is it better to keep the group that is more likely to respond as a Group reference or shall I swap? Your help will be much appreciated.

Many Thanks

Analysis of Maximum Likelihood Estimates | ||||||

Parameter | DF | Estimate | Standard | Wald | Pr > ChiSq | |

Error | Chi-Square | |||||

Intercept | 1 | -6.994 | 0.0779 | 8060.583 | <.0001 | |

VAR1 | 1,2,5,9,11,. | 1 | -0.0645 | 0.0204 | 10.0047 | 0.0016 |

VAR2 | -2,2,1,8 | 1 | 0.2587 | 0.0222 | 135.8357 | <.0001 |

VAR3 | <7145.5 | 1 | 0.2042 | 0.0295 | 47.89 | <.0001 |

VAR4 | 784.5 To 894.5 or Miss | 1 | -0.2501 | 0.035 | 51.186 | <.0001 |

VAR4 | <784.5 | 1 | 0.3376 | 0.0278 | 147.6797 | <.0001 |

VAR5 | 1,. | 1 | 0.2385 | 0.0277 | 74.1201 | <.0001 |

VAR6 | <1106.5 | 1 | 0.3637 | 0.0509 | 51.01 | <.0001 |

VAR7 | 0,. | 1 | 0.1021 | 0.0357 | 8.1737 | 0.0043 |

VAR8 | 11,. | 1 | -0.3077 | 0.0431 | 50.8802 | <.0001 |

VAR8 | 3,4,7,8 | 1 | 0.133 | 0.0303 | 19.2755 | <.0001 |

VAR8 | 9,10,12,13 | 1 | -0.084 | 0.0353 | 5.6456 | 0.0175 |

VAR9 | 1 | 1 | -0.3008 | 0.0875 | 11.811 | 0.0006 |

VAR9 | 2 or Miss | 1 | 0.1234 | 0.0414 | 8.8989 | 0.0029 |

VAR9 | 3 | 1 | 0.0998 | 0.0388 | 6.6322 | 0.01 |

VAR10 | 0,. | 1 | 0.3695 | 0.047 | 61.7212 | <.0001 |

Accepted Solutions

Solution

11-19-2013
01:01 PM

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Highlight
- Email to a Friend
- Report Inappropriate Content

Posted in reply to Kanyange

11-19-2013 01:01 PM

Good afternoon - in general, here are some things to keep in mind when choosing a reference group:

1. sample size (you don't want your reference group to have a much smaller sample size in comparison to the non-reference group(s))

2. the definition of the group: it should be a well-defined group (that is, not something like "other")

3. utility (maybe it is the control group, or the most important for some reason, etc.)

All Replies

Solution

11-19-2013
01:01 PM

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Highlight
- Email to a Friend
- Report Inappropriate Content

Posted in reply to Kanyange

11-19-2013 01:01 PM

Good afternoon - in general, here are some things to keep in mind when choosing a reference group:

1. sample size (you don't want your reference group to have a much smaller sample size in comparison to the non-reference group(s))

2. the definition of the group: it should be a well-defined group (that is, not something like "other")

3. utility (maybe it is the control group, or the most important for some reason, etc.)

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Highlight
- Email to a Friend
- Report Inappropriate Content

Posted in reply to lryan

11-19-2013 04:38 PM

Thank you Laura for your response...So the sign of the estimate doesn't matter then....What I mean, if the estime sign is negative, I shouldn't need to change the reference group and make the estimate positive...

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Highlight
- Email to a Friend
- Report Inappropriate Content

Posted in reply to Kanyange

11-20-2013 12:57 PM

You are welcome; I am glad it was helpful.

The sign of the estimate matters in that it tells you how that category changes the probability of success (or the probability of a particular level of the response). The relationship between the level of the response for a given category is not going to change based on what level you select to be the reference group. The perspective is all relative.