Query: The modelers confused cause and effect, thereby getting the feedback in the wrong direction."

Relevant passages:
Correlation does not imply causation <=SEP=> In statistics , many statistical tests calculate correlations between variables and when two variables are found to be correlated , it is tempting to assume that this shows that one variable causes the other . That `` correlation proves causation , '' is considered a questionable cause logical fallacy when two events occurring together are taken to have established a cause-and-effect relationship . This fallacy is also known as cum hoc ergo propter hoc , Latin for `` with this , therefore because of this , '' and `` false cause . '' A similar fallacy , that an event that followed another was necessarily a consequence of the first event , is the post hoc ergo propter hoc ( Latin for `` after this , therefore because of this . '' ) fallacy .   For example , in a widely studied case , numerous epidemiological studies showed that women taking combined hormone replacement therapy ( HRT ) also had a lower-than-average incidence of coronary heart disease ( CHD ) , leading doctors to propose that HRT was protective against CHD . But randomized controlled trials showed that HRT caused a small but statistically significant increase in risk of CHD . Re-analysis of the data from the epidemiological studies showed that women undertaking HRT were more likely to be from higher socio-economic groups ( ABC1 ) , with better-than-average diet and exercise regimens . The use of HRT and decreased incidence of coronary heart disease were coincident effects of a common cause ( i.e. the benefits associated with a higher socioeconomic status ) , rather than a direct cause and effect , as had been supposed .   As with any logical fallacy , identifying that the reasoning behind an argument is flawed does not imply that the resulting conclusion is false . In the instance above , if the trials had found that hormone replacement therapy does in fact have a negative incidence on the likelihood of coronary heart disease the assumption of causality would have been correct , although the logic behind the assumption would still have been flawed . Indeed , a few go further , using correlation as a basis for testing a hypothesis to try to establish a true causal relationship ; examples are the Granger causality test and convergent cross mapping .

Hawthorne effect <=SEP=> The Hawthorne effect ( also referred to as the observer effect ) is a type of reactivity in which individuals modify an aspect of their behavior in response to their awareness of being observed . The original research at the Hawthorne Works in Cicero , Illinois , on lighting changes and work structure changes such as working hours and break times was originally interpreted by Elton Mayo and others to mean that paying attention to overall worker needs would improve productivity . Later interpretations such as that done by Landsberger suggested that the novelty of being research subjects and the increased attention from such could lead to temporary increases in workers ' productivity . This interpretation was dubbed `` the Hawthorne effect '' .

Positive feedback <=SEP=> Positive feedback is a process that occurs in a feedback loop in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation .  That is , A produces more of B which in turn produces more of A . In contrast , a system in which the results of a change act to reduce or counteract it has negative feedback . Both concepts play an important role in science and engineering , including biology , chemistry , and cybernetics .   Mathematically , positive feedback is defined as a positive loop gain around a closed loop of cause and effect .  That is , positive feedback is in phase with the input , in the sense that it adds to make the input larger .  Positive feedback tends to cause system instability . When the loop gain is positive and above 1 , there will typically be exponential growth , increasing oscillations , chaotic behavior or other divergences from equilibrium . System parameters will typically accelerate towards extreme values , which may damage or destroy the system , or may end with the system latched into a new stable state . Positive feedback may be controlled by signals in the system being filtered , damped , or limited , or it can be cancelled or reduced by adding negative feedback .   Positive feedback is used in digital electronics to force voltages away from intermediate voltages into ' 0 ' and ' 1 ' states . On the other hand , thermal runaway is a positive feedback that can destroy semiconductor junctions . Positive feedback in chemical reactions can increase the rate of reactions , and in some cases can lead to explosions . Positive feedback in mechanical design causes tipping-point , or ` over-centre ' , mechanisms to snap into position , for example in switches and locking pliers . Out of control , it can cause bridges to collapse . Positive feedback in economic systems can cause boom-then-bust cycles . A familiar example of positive feedback is the loud squealing or howling sound produced by audio feedback in public address systems : the microphone picks up sound from its own loudspeakers , amplifies it , and sends it through the speakers again .

Network effect <=SEP=> In economics and business , a network effect ( also called network externality or demand-side economies of scale ) is the effect that one user of a good or service has on the value of that product to other people . When a network effect is present , the value of a product or service is dependent on the number of others using it .   The classic example is the telephone . The more people who own telephones , the more valuable the telephone is to each owner . This creates a positive externality because a user may purchase a telephone without intending to create value for other users , but does so in any case . Online social networks work in the same way , with sites like Twitter and Facebook becoming more attractive as more users join .   The expression `` network effect '' is applied most commonly to positive network externalities as in the case of the telephone . Negative network externalities can also occur , where more users make a product less valuable , but are more commonly referred to as `` congestion '' ( as in traffic congestion or network congestion ) .   Over time , positive network effects can create a bandwagon effect as the network becomes more valuable and more people join , in a positive feedback loop .