The thesis statement should clearly state the focus of the cause and effect essay in order for your readers to know exactly what your paper will discuss. To this end, use the words "cause" or "effect" within your thesis. For instance, "Spending too much time on the Internet causes cognitive impairment." Avoid ambiguous wording that leaves audiences stumped as to your meaning.
Cause and effect essays are meant to either analyze the relationship of multiple subjects or to inform the audience. Furthermore, cause and effect essays are either organized chronologically or in order of importance to the topic. The purpose of the essay should be clearly defined by cause keywords, such as "because of," "due to," "since" and "leads to." Keywords for effect include: "consequently," "as a result of," "thus," "resulting in" and "therefore."
Good thesis statements have a focus that narrows down a topic to be developed successfully within the body of the essay. For instance, the general topic of environmentalism would have a thesis along the lines of, "Pesticides used in Argentina affect the health of people in America." The thesis is focused enough to discuss a specific attribute of environmentalism without being too broad or vague. A thesis that lacks focus would suggest something like, "Most people are unaware of the positive effects of going green."
The most important part of a well-defined working thesis is that it can be supported by evidence. If the essay is to be effective, your argument must be supported by facts and examples. Unsupported claims give the essay (and author) a lack of credibility. Each cause and effect relationship has to be backed up with thorough evidence or qualifying statements such as, "The evidence suggests," "It seems likely" or "The apparent cause." Remember that your credibility depends partly on the strength and validity of the evidence you put forth.