Ans. is 'b' i.e., Unethical to use in animal Experimental epidemiology (Epidemiological Experiments) Experimental epidemiology is also called trial. Broadly speaking, a trial refers to putting something to a test. This allows the term to be used in reference to a test of a treatment for the sick or a test of a preventive measure intended to ave illness, injury or disease. Therefore, the defining feature of an experimental study is its ability to allocate or assign interventions or treatment to experiment unit. In simple words, the study of a treatment (Drugs, surgical intervention) or preventive measure (e.g. vaccination) on living subjects is known as experimental study or trial. Assignment of treatments may be based on i) Randomization In randomized controlled trials ii) Non-randmization trails There are following types of experimental trials 1. Clinical trials: Used to evaluate treatment for people who are ill (e.g. a clinical trial of a chemotherapeutic agent) 2. Field trails: Used to evaluate interventions to prevent disease in healthy people (e.g. a field trial of a vaccine). 3. Community trial: Used to evaluate community-wide intervention (e.g. a community trail of the effects of fluoridation of public water supply). 4. Animal Study: When clincial trails are done on animals (instead of human) is called animal study. In an experimental study, the investigator assign individuals in experimental group and reference group and then follows the two groups for the outcome of interests. Therefore, experimental study is prospective study. Before staing any experimental study the approval of ethics committee is required. The poocol of study is submitted to ethics committee and ethics committee gives approval to the studies which are ethical. So, all experimental studies are considered ethical (after taking approval of ethics committee). There are fewer ethical restrains on experimental study in animals than in human. Blinding in experimental study: Blinding is a procedure to avoid bias i) In single blinding, study subjects are not aware of the treatment they are receiving (whether of experimental group treatment or reference group treatment). ii) In double blinding, study subjects as well as investigator are not aware of the treatment study subject are receiving. iii) In Triple blinding, study subjects, investigator as well as analyzer are not aware of the treatment study subjects are receiving. It is not always possible to do blinding. For example in a trial of surgical intervention, the surgeon and the patient will always know about the surgical procedure as it is necessary to explain the patient to take consent for surgery. Of course, in animal study, the animals do not have awareness or expectancies about their assignment to experimental or reference group. So, we do not use terms single blinding and double blinding. In animal study, when the investigator is not aware of which subjects are in which experiments group, it is simply called a blind study. Interim analysis An interim analysis is the assessment of data during follow up stages of a study for the purpose of assessing the performance of the study. If there is convincing enough evidence to say that there is a significance large treatment difference, study can be stopped at a point earlier than the planned end point. Therefore, interim analysis is also known as 'data dependent stopping' or 'early stopping' There are two main reasons for early stopping of study (interim analysis): 1. Ethical: We want to make sure that the maximum number of patients receive the most effective treatment at the earliest stage. So, if we have convincing evidence that the treatment of study has significant treatment difference, study is closed early and the treatment can be approved so that other patients (in outside world) can receive effective treatment early. 2. Economic: We do not want to spend extra money if we already have enough evidence (in interim analysis) to stop study early. Since clinical trials are expensive, interim analysis can reduce the expenditure by shoening of follow up time needed to make a conclusion.