A recurrent theme in this thesis has been that psychologists do not have access to theory that is as useful for prediction-making as the body of theory applied by climatologists. The theory used by climatologists is capable of predicting (albeit with uncertainty) the magnitude and timing of future climatic changes. It can also be used to directly produce these predictions, without the use of statistical models trained on
empirical data. It is unrealistic to expect that in the foreseeable future psychologists will produce quantitative theory of comparable sophistication and usefulness. Indeed, most psychological theory is not quantitative at all, but rather constituted of verbal statements about behaviour (Myung & Pitt, 2002). It is nevertheless the case that psychologists can develop and apply theory that facilitates the making of useful predictions—even if the theory applied is not capable of producing these predictions without help from statistical models trained on empirical data.
One situation in which a theory can be used to facilitate prediction is if the theory identifies causal effects that can be empirically estimated, and where knowledge of those causal effects can be used to generate useful predictions. For example, a theoretical framework describing how climate change may impact mental health was proposed by a group of Australian researchers (Berry et al., 2010). As discussed
previously (see section 1.2.2.1), Berry and colleagues’ framework suggests that adverse weather events occurring as part of climate change can impact mental health directly (e.g., by causing trauma); via economic, social and demographic impacts on
communities that subsequently impact mental health; and via impacts on physical health that subsequently affect mental health. A strength of this model is that it specifies causal relationships between variables that can be estimated empirically in real-world contexts (albeit with necessary uncertainty) and that can be used to generate predictions about behaviours of genuine substantive interest.
As an example of how Berry and colleagues’ (2010) model could be used to generate useful predictions, we could take a particular indicator of mental health that was studied in the empirical section of this thesis (suicide rates). In their model, one of the pathways via which climate change may impact mental health is via effects of climate change on economic productivity, which may subsequently affect mental health. The future impact of climate change on economic productivity can be estimated (see N. Stern, 2007), and so too can the impact of economic productivity on suicide rates (M. Berk, Dodd, & Henry, 2006; Chang, Gunnell, Sterne, Lu, & Cheng, 2009; B. Yang, Lester, & Yang, 1992). Obviously these estimates come with a non-trivial magnitude of uncertainty, and for present purposes it is not necessary to attempt a substantive
synthesis of the research on these topics. Nevertheless, these estimates could be
combined to make predictions about the effect of climate change on suicide rates—or at least of the effect occurring via the pathway of climate change effects on economic productivity. The theoretical framework can be applied in this way because the
framework is made up of a sequence of proximal causal effects that can be estimated, and estimates of these proximal effects can be used to make predictions about the size of a distal effect (of climate change on suicide rates) that is of genuine substantive interest.
The advantage of drawing on theory for facilitating predictions is that it allows for the prediction of effects that may occur as a result of sustained climate change in the future, but that do not currently occur as a result of normal climatic variation. For example, normal temperature variation currently has little relationship with economic productivity (at least in wealthier countries; see Dell, Jones, & Olken, 2012). However, sustained climate change may have substantial effects on economic productivity (N. Stern, 2007). This means that the effect that sustained future climate change will exert on suicide rates via the pathway of impacting economic productivity is likely not
captured by analyses of the effects of normal temperature variation on suicide. Provided that the effect of sustained climate change on economic productivity can be predicted (likely by drawing on work by researchers in other fields), and the effect of economic productivity on suicide rates can be estimated, then the size of the effect of climate change on suicide rates that may occur via the pathway of economic effects can actually be predicted. Such predictions are facilitated by the use of theory, and would not be possible simply by observing correlations between climatic variables and suicide rates. Use of theory in this way may also facilitate the study of impacts of climate change on psychological variables that occur slowly and that are mediated via wider societal processes and phenomena.
In sum, theories can be developed that facilitate the making of practical and useful predictions. However, to do so they need to be constructed in such a way that they specify causal effects that are estimable, and that can be used to make predictions about behaviours of substantive interest. To achieve this, psychologists may need to prioritise prediction (as opposed to explanation) when developing and applying theory. In general, the suggested focus on a theory’s capacity to make useful predictions aligns well with an instrumentalist stance toward psychological theory (see Cacioppo, Semin, & Berntson, 2004).