The type of sampling ensures that bias is eliminated from the study because any systematized error is eliminated. This ensures that the results of the study could be considered to be valid and containing known error. Probability sampling methods utilize randomization in the selection of the sample elements. With a probability sampling method the researcher is aware of the probability of each member of the sample being chosen. In essence each member has the same probability of selection. There are times however where sampling is done without replacement and while each member does not have the same probability the difference is negligible so that it does not influence the study negatively. When a researcher uses non-probability sampling methods the researcher is unaware of the chance of selection of each member of the sample. Consequently the researcher...

The dependent variable was also measured at the ratio level. The dependent variable was death or numbers of persons who died or had particular debilitation conditions. Thus the dependent variable was also measured at the ratio level. The level of measurement ensures that the most powerful statistical test could be employed to assess the hypotheses. Consequently, any difference between the groups should be identified by these tests. This knowledge enhances the findings of the study and give them greater validity.
References

Russell a.J. et al. (2008). Vasopressin vs. Norepinephrine Infusion in Patients with Septic

Shock. New England Journal of Medicine 358 (9): 877-887.