21. In contrast, an observational study does not involve experimental manipulation. 22. For the majority of questions, we have no choice but to use observational studies , 23. Well-publicised observational studies find that first borns have slightly higher IQ than later borns. 24. Several very large observational studies have also found elevated risk of heart attack from rofecoxib. 25. We need to look at all the available data and not discount the observational studies . 26. That's what you can't tell from observational studies ." 27. Observational studies show a strong association between delayed intestinal transit and the production of methane.28. However, observational studies have raised concerns about negative effects of weight loss and weight cycling. 29. This is done through repeatable experiments or observational studies . 30. The negative effects are found in several observational studies .
