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CONTEXT EFFECTSIs it reasonable to expect that the causal relationships that were established in afactory would also apply in an office environment? Are the findings that wereobtained in a military camp also applicable to a university residence? Thesetting within which research is conducted can have an important bearing uponthe generalizability of the findings. More specifically, it ought also to beobvious that findings which are based upon laboratory conditions cannotsimply be made applicable to natural environments.Free download from www.hsrcpress.ac.zaPERIOD EFFECTSThe effect associated with the time at which research is conducted is obviouslynot only to be found in studies of universal interest. Nonetheless, it is likelythat they have the most far-reaching consequences in this case.Is it, for example, possible to regard a study that was conducted on a specificday or during a given month and year as valid for all time? Studies of asociopolitical and economic nature are evidently particularly sensitive as far asthe time of the year and the specific year during which they are conducted areconcerned! Events such as elections and assassinations, and conditions such aseconomic recessions, all influence people’s attitudes, convictions, andperceptions.Selection effects have a direct bearing upon the representativeness of thesample. Context and period effects are more closely associated with therepresentativeness of the circumstances under which the research wasconducted. As far as the former is concerned, the standard answer to theproblem in the social sciences is to be found in the principles of samplingdesign. Because of the fact that external validity is such a difficult, but at thesame time, important consideration in social scientific research, a considerableamount of attention has been paid to the development of measures by means ofwhich sampling may be optimally done. The basic principle is that of randomsampling. If every element in the population has an equal opportunity of beingselected as part of the sample, the chances are that much greater that thesample will, in fact, be representative of the defined population. By the verynature of things, the ideal of random sampling is not always attainable, and as aresult non-random techniques have to be employed. In situations of this natureit is, strictly speaking, not possible to accept that the eventual sample isrepresentative of the defined population, and there must then necessarily besome doubt concerning the generalizability of the findings.The most important guideline concerning context and period effects is that ofvariation. The researcher ought, as far as possible, to vary the circumstances,design, period, and so on. It is only by the use of repeated measurement underdifferent circumstances and during different periods that it is possible tocontrol for these effects.120