模型选择仅放回拦截模型
我正在用冠心病与几个变量对模型进行逻辑回归（请参阅数据框架）。
ind sbp tobacco ldl adiposity typea obesity alcohol age chd
1 1 160 12.00 5.73 23.11 49 25.30 97.20 52 1
2 2 144 0.01 4.41 28.61 55 28.87 2.06 63 1
...
我在此模型上进行了逐步选择以接收最佳模型，但是结果我只包含截距。为什么会呢？这是什么意思？
model <-glm(chd ~ ., data = CHD, family = "binomial"(link = logit))
intercept_only <- glm(chd ~ 1, data=CHD, family = "binomial"(link = logit))
#perform backward stepwise regression
back <- step(intercept_only, direction='backward', scope=formula(model), trace=0)
#view results of backward stepwise regression
Step Df Deviance Resid. Df Resid. Dev AIC
1 NA NA 461 596.1084 598.1084```
I am performing logistic regression on the model with CHD sickness vs a few variables (see the data frame).
ind sbp tobacco ldl adiposity typea obesity alcohol age chd
1 1 160 12.00 5.73 23.11 49 25.30 97.20 52 1
2 2 144 0.01 4.41 28.61 55 28.87 2.06 63 1
...
I performed backward stepwise selection on this model to receive the best model, but I get as the result the model that contains only the intercept. Why can it be? What does it mean?
model <-glm(chd ~ ., data = CHD, family = "binomial"(link = logit))
intercept_only <- glm(chd ~ 1, data=CHD, family = "binomial"(link = logit))
#perform backward stepwise regression
back <- step(intercept_only, direction='backward', scope=formula(model), trace=0)
#view results of backward stepwise regression
Step Df Deviance Resid. Df Resid. Dev AIC
1 NA NA 461 596.1084 598.1084```
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要进行后退回归，您应该从包含变量的模型开始，而不是仅具有截距的模型：
back＆lt; - step（model，direction ='backward'，scope = formula（model），trace = 0 ）intercept_only仅在设置direction ='forthrow'o或direction ='两个''时才能使用模型。To do backward regression, you should start with a model that contains variables, rather than the model with intercept only:
back <- step(model, direction='backward', scope=formula(model), trace=0)The
intercept_onlymodel should only be used if you setdirection='forward'ordirection='both'.