Question: Probit Regression modelling in R
0
11 months ago by
krushnach80470
krushnach80470 wrote:

I have already made a post in stack, wont; make a duplicate here, so Im giving the link here probit modelling question

I would be really glad if I get input about it since im not sure if im doing it correctly or not ..

``````so df is my original data frame so ,im making d2 to change my sample into factors
``````
``````  conc<- c(6 , 5, 4,3,2,1,0,-1,-2)
IMRS <- c(1,1,0.23,1,1,0.8,0.4,0.5,0.0)
S18S <- c(1,1,.69,1,1,0.33,0.4,0.0,0.0)
df <- data.frame(conc,IMRS,S18S)

conc IMRS S18S
1    6 1.00 1.00
2    5 1.00 1.00
3    4 0.23 0.69
4    3 1.00 1.00
5    2 1.00 1.00
6    1 0.80 0.33

library(tidyr)
d2=gather(df,SAMPLE,y,IMRS,S18S,factor_key=T)

conc SAMPLE    y
1    6   IMRS 1.00
2    5   IMRS 1.00
3    4   IMRS 0.23
4    3   IMRS 1.00
5    2   IMRS 1.00
6    1   IMRS 0.80

summary(glm.out)

library(ggplot2)
lr_data <- data.frame(predictor=glm.out\$linear.predictors,
prob=glm.out\$fitted.values, SAMPLE=d2\$SAMPLE)

ggplot(lr_data, aes(x=predictor, y=prob, color=SAMPLE)) + geom_point(size=10)+
geom_line(linetype = "dashed",lwd = 0.5)+geom_hline(yintercept = 0.65)
``````

Build a model that predicts the level of your dependent variable (x) based on concentration (y)

So am i doing it in opposite manner ? or it wont matter .let me know

``````"Predict values from the model using predict()"
``````

Can you plug that into my code how do i use or do that? because I been through the tutorials im not sure/cofident about using the

``````predict()
``````
R • 417 views
modified 11 months ago • written 11 months ago by krushnach80470
1

Hi Krushnach, there is not enough information provided - perhaps not even you is sure of the experiment? It is also confusing (looking at the post on StackExchange) because you produce an object called `df` and then one called `d2`. From where did you obtain the figure that you posted?

The standard procedure would be:

1. Build a model that predicts the level of your dependent variable (x) based on concentration (y)
2. Predict values from the model using `predict()`
3. Plot the original values and also the predicted values to see how they fit (visually)

updated my question with code..the figure i got from a paper where they did this probit analysis

Okay, can you share the paper? I am interested to see it

hi kevin I don;t have acess to that figure i followed your procedure and I get something similar to that

`````` curve(plogis( 0.1792 + 0.8259*x), min(df\$A),
``````

Since i took the example from stack I wanted to ask what is the equivalent of this `plogis` for probit ?

1

Whoever up-voted @Kevin's comment above should consider the following.

Upvoting posts/comments is meant to be used in cases where the content of the post/comment contributes to solving original question/adds useful information. Upvoting "can you share the paper?" above does not help anyone and is a misuse of the voting system.

okay im sorry i hit it, my apology now i reversed it

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