List three reasons why a study may be considered invalid

1.- Improper Information

2.- Not doing trials again to prove it.

3.- Because most studies are pushed to be published to it can have missing information.

Three things why a study can be considered invalid might be:

Lack of Research: if a study does not achieve the requirements of the research method then it is not valid.  

Biased opinions: if a study is based on one specific way of the researcher then in characterized as invalid.  

No evidence: if the study does not have enough or not at all evidence of what it was investigated then it cannot be reliable and so, invalid.  

the percentage of students at the school need special diets is

c) 10 percent

it allows shippers to carry commercial goods, which allows them to save time and money.