Download presentation

Presentation is loading. Please wait.

Published byAaron Maw Modified over 2 years ago

1
Statistical Analysis SC504/HS927 Spring Term 2008 Session 6: Week 22: 29 th February OLS (3): multiple regression and dummy coding

2
2 Example from Suicide data:

3
3 E.g.: Using the data set alcohol

4
4 Hierarchical Regression

5
5 ‘Dummy’ variables variables given the values 1 or 0 typically to indicate ‘yes’ or ‘no’ e.g. 1=‘female’ 0=‘not female’ (i.e. male) Dummy coding will change the value of the constant (intercept) but NOT the gradient (b) NB: create one dummy variable even though there are two possible genders

6
6 Working out Predicted Y Value You need to work out 2 regression equations If Females = 1, then: Y = a + b 1 (age) + b 2 (1) If Males = 0, then: Y = a + b 1 (age) + b 2 (0)

7
7 dummy variables with multiple categories suppose you want to investigate the effect of housing tenure you have a variable coded: 1=owns outright 2=owns with a mortgage 3=part owns, part rents 4=rents 5=rent free NB: the coding is arbitrary. You could have 5=owns outright. 3= owns with a mortgage, 1=rents, 2=rent free, 4=part owns, part rents

8
8 Multiple categories (cont) If the categorical variable has z categories, create z-1 dummy variables e.g. d 1 =1 if owns with a mortgage, 0 otherwise d 2 =1 if part owns, part rents, 0 otherwise d 3 =1 if rents, 0 otherwise d 4 =1 if rent free, 0 otherwise The omitted category is known as the ‘reference’ or ‘baseline’ category each case will have a maximum of one dummy coded 1, outright owners will have them all coded 0

9
9 Choice of reference category Any category can be the reference Choose for ease of and meaningful interpretation e.g. the ‘norm’ or most common category the majority ethnic group in a study of the consequences of being from a minority ethnic group unemployed people if you are studying the effects of unemployment

Similar presentations

OK

1 AAEC 4302 ADVANCED STATISTICAL METHODS IN AGRICULTURAL RESEARCH Chapter 7.3 Dummy Variables.

1 AAEC 4302 ADVANCED STATISTICAL METHODS IN AGRICULTURAL RESEARCH Chapter 7.3 Dummy Variables.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on relations and functions for class 11th sample Ppt on telephone exchange in indian railways Gastrointestinal tract anatomy and physiology ppt on cells Ppt on history of cricket for class 9 What does appt only meaning Ppt on cell structure for class 8 Ppt on spirit of unity in india Ppt on wind energy Ppt on save environment slogans Ppt on viruses and bacteria test