A valid conclusion is one that naturally follows from informed, formulated hypotheses, prudent experimental design, and accurate data analysis.
If an argument is invalid, then it must have at least one false premise. If an argument has a conclusion that is certainly false, then the argument must be invalid. If the premises and conclusion are all false, the argument must be invalid.
A biased sample occurs when the group selected for a statistical study or survey is not random and doesn't properly represent the larger population. This is a result of sampling bias which occurs when the sample of the population is not representative of the population at large.
If an overestimate or underestimate does happen, the mean of the difference is called a “bias.” In more mathematical terms, an estimator is unbiased if: That's just saying if the estimator (i.e. the sample mean) equals the parameter (i.e. the population mean), then it's an unbiased estimator.
Cohort studies are an appropriate study design when: (1) there is good evidence to suggest an association between an exposure and an outcome (perhaps through prior cross-sectional studies); (2) the interval between exposure and development of the outcome is relatively short to minimize loss to follow-up; and (3) the outcome is not too rare (so that the size of the cohort is reasonable).
Hence,
No actual study was done, only observation.
From the above explanation, we can say that
The conclusion drawn from the study is not valid because the sample is Biased.In this instance, an inappropriate study was conducted