Nonexperimental studies

There are two fundamental types of study design experimental and nonexperimental (Piantadosi, 2005). Piantadosi defines an experiment as a series of observations made under conditions in which the influences of interest are controlled by the research scientist. This book deals largely with experimental studies. In nonexperimental studies, the research scientist collects observations but does not exert control over the influences of interest. Nonexperimental studies are often called observational studies, but this term is inaccurate it does not definitively distinguish between nonexperimental studies and experimental studies, in which observations are also made. Some nonexperimental study designs are discussed in Chapter 13. 

A cohort study is a nonexperimental study (recall Section 5.5 for discussion of experimental and nonexperimental studies) that collects information from an identified group of individuals in an overall population. Cohort studies are used widely in epidemiology and clinical epidemiology, and, as Haynes et al. (2006) noted, evidence from cohort studies (also known as cohort analytical studies) is the next most powerful method after the controlled trial (see also Fletcher and Fletcher, 2005 Webb et al, 2005 Woodward, 2005). 

Grade A, meta-analysis of randomised, controlled trials or from at least one randomised, controlled trial, or from at least one well designed, controlled study without randomisation grade B, from at least one other type of well designed, quasi-experlmental study, or from well designed, nonexperimental studies (e.g. comparative studies, correlation studies, case-control studies) grade C, from expert committee reports/opinions and/or clinical experience of authorities, ND, not demonstrated. Data from the Royal College of Physicians and the Bone and Tooth Society. 

Directly based on at least one controlled study without randomization or at least one other type of v quasiexperimental study, or extrapolated from RCTs Directly based on nonexperimental studies or extrapolated from RCTs or nomandomized studies Directly based on expert reports or opinion or experience of authorities, or extrapolated from RCTs, nonrandomized studies, or nonexperimental studies... 

In Section II above we presented all the required formulas for carrying out statistical mechanical calculations of the thermodynamic properties and discussed their limitations. These were the procedures pioneered in the 1930s and 40s, mainly by Pitzer and his associates. This approach culminated in the compilation of SWS, but is no longer widely used because of the unavailability of the fundamental spectroscopic constants (vibrational frequencies and torsional barriers) for most hydrocarbons. The numerous published attempts to reconcile calculated properties of ethane with experimental values attest to the difficulties inherent in this approach. Nonexperimental studies have instead pursued approximate semiempirical methods, with very good results. 

One example of a nonexperimental study is the cohort study. A cohort study is a nonexperimental smdy that collects information from an identified group of individuals in an overall population, such as those receiving the marketed drug of interest (see Gamble 2014). Other smdy designs include case-control studies, cross-sectional studies, and ecological smdies. Case reports and case series can also be informative. 

Shrout PE, Bolger N. 2002. Mediation in experimental and nonexperimental studies. New procedures and recommendations. Psychol Methods 7 422—445. 

Phase IV. Studies or trials conducted after a medicine is marketed to provide additional details about the medicine s efficacy or safety profile. Different formulations, dosages, durations of treatment, medicine interactions, and other medicine comparisons may be evaluated. New age groups, races, and other types of patients can be studied. Detection and definition of previously unknown or inadequately quantified adverse reactions and related risk factors are an important aspect of many Phase IV studies. If a marketed medicine is to be evaluated for another (i.e., new) indication, then those clinical trials are considered Phase II clinical trials. The term postmarketing surveillance is frequently used to describe those clinical studies in Phase IV (i.e., the period following marketing) that are primarily observational or nonexperimental in nature, to distinguish them from well-controlled Phase IV clinical trials or marketing studies. 

Epidemiological studies are nonexperimental trials and involve an investigation of various individuals or groups of subjects as they happen to have been exposed. Endpoints generally measured include mortality, morbidity, medical visits or hospital admissions, and/or clinical signs and symptoms. 

Several conclusions emerge from this study. First, while patients can be active agents in influencing the treatment they receive, physicians differ systematically in their propensity to prescribe an antidepressant. In this sense, the experimental and nonexperimental findings on DTCA affecting overall therapeutic class sales, but not shares within the class, are consistent. 

Both nonexperimental and experimental studies reveal that while DTCA increases the size of the overall sales of a particular therapeutic class, brand-specific DTCA does not appear to have a statistically significant impact on the share of any particular brand within the therapeutic class. By increasing the size of therapeutic class sales but not affecting shares within the class, DTCA has ambiguous effects on consumer welfare. In particular, there is some experimental evidence suggesting that in the case of antidepressants. 

One of the first studies of the Harvard group was to investigate the effects of psilocybin on normals in a nonclinigal, nonexperimental but warm, supportive setting. Results were evaluated by a questionnaire, which showed that 88% of their subjects. . . reported that they had learned something of value about themselves and the world, while 62% claimed the experience of psilocybin changed their lives for the better. (Leary et al. 1963). 

In the approximately 70 years since the discovery of the toxic G agents and 50 years since the subsequent development of the V agents, humans have only occassionally served as test subjects in laboratory studies designed to determine threshold toxic effects associated with low-level (nonlethal) sarin and VX vapor exposures (2-10 min) (Johns, 1952 Sim, 1956 Bramwell et al., 1963). In addition, although the toxic effects of accidental exposures and nonexperimental exposures from terrorist or military attacks are documented, critical information related to the exposure conditions can only be estimated at best. Thus, estimates of human dose-responses to nerve agent vapor exposures from such sources are often associated with significant uncertainty and are of limited utility in predicting health hazard risks. 

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