Correct

多半 vs 大半

/ duōbàn vs dàbàn /
Strokes

Definition

多半 and 大半 both Adverb or Noun, which means “probably; majority".

Example

多半 and 大半 as Adverbs both mean "most probably", and usually do not precede the subject of a sentence.
Here, the two words 多半 and 大半 are interchangeable.

In terms of frequency of usage; however,多半 is more frequently used.
1
duōbàn
多半
  
(
bàn
大半
  
)
shì
zuì
喝醉
le
  

He was probably drunk.

2
Míngtiān
明天
duōbàn
多半
  
(
bàn
大半
  
)
huì
qíng
de
  

It is probably going to be clear tomorrow.

3
wánchéng
完成
xué
学业
  
,
duōbàn
多半
  
(
bàn
大半
  
)
shì
kào
ge
哥哥
de
zhù
资助
  

She finished her school mainly with her brother's help.

多半 and 大半 as Nouns, mean "the greater part", and 一 can be added.
In examples ④ and ⑤, 多半 and 大半 are used as adverbials, the same as that in examples ① ② and ③, but the meaning is different.
4
Zhè
běn
xiǎoshuō
小说
hěn
yǐn
吸引
rén
  
,
xiàzi
下子
jiù
kàn
le
bàn
大半
  
(
duōbàn
一多半
  
)
  

The novel was appealing to me and I read much of it at one sitting.

5
Lái
cānjiā
参加
huì
大会
de
rén
  
,
duōbàn
多半
  
(
bàn
大半
  
)
shì
xuésheng
学生
  

Most of the meeting participants are students.

6
men
我们
bān
de
tóngxué
同学
duōbàn
多半
  
(
bàn
大半
  
)
shì
nánfāng
南方
rén
  

Most of the students in our class are from the south.