Discuss the validity of the trend observed in the following scenario. List 2 factors with a brief explanation (sample size, sampling technique, extraneous or hidden variables, bias, etc.) which could affect the study.
Barney drinks a V-8 juice every day. Over a 2-day period, Barney ran out of V-8 and noticed he was very tired and irritable. Barney concluded that the absence of the 8 essential vegetables drink in his diet caused his tiredness and irritability.