I wrote an essay last year of high school that partly touched on the Stinger missile effectiveness during the Soviet-Afghan War. Here's an excerpt if you're interested. Warning! Wall of text incoming:

In July 1986 a cable from the CIA’s Islamabad station warned that the pace of the mujahedin attacks appeared to be slowing under the relentless helicopter assaults mounted by Soviet Spetsnaz forces, especially along the Pakistani border. Some at the agency feared that the new Soviet assault tactics were tipping the war’s balance against the mujahedin. On September 26, 1986, a new type of antiaircraft weapon was supplied to the mujahedin. Powered by batteries and guided by a portable heat-seeking system, the FIM-92 Stinger MANPAD was the best of its kind at the time. Its infrared tracking system made it impervious to countermeasures normally taken by Soviet pilots.

After its introduction, the Stinger missile threat forced Soviet and DRA helicopters and jets to fly at a higher altitude than previously, and as a result the Soviets lost some of their accuracy when conducting air assaults. The Soviets did not however lose much of their operational capabilities, and the level of Soviet/DRA air assaults remained constant.

The stinger missile is often credited with turning the tables and ‘winning the war’ for the U.S., and it has become widely accepted as one of the decisive factors causing the Soviet withdrawal. However, comparing the number of aircraft lost by Soviet and DRA forces with the estimated number of Stinger missiles fired shows that the Stinger’s success rate was in the meager 20% range, instead of the 70-80% that has been widely accepted previously. Reports about the Stinger’s effectiveness were often also exaggerated. The mujahedin were required to report hits in order to receive more Stinger missiles, which made them unwilling to admit less than perfect performance, even though that was not always the case. Although the Stinger did shoot down around 150 Soviet aircraft and made the Soviets rethink their aerial strategy, most analysts refute the idea that the Stinger had any significant influence on the course of the war.

Note: There are a vast number of different estimates on the number of Soviet aircraft that the Stinger missile shot down during the war. However, most of these claims are unrealistic. Taking into account all available statistics concerning the estimated numbers of fired Stingers and Soviet aircraft losses, 150 is the highest credible number of downed Soviet aircraft that the Stinger can be credited with, considering its 20% success rate.