Relative strength index in Stock market; Importance and calculation of RSI

 Like MACD, Relative strength index (RSI) is also a technical indicator used in financial markets. It was introduced in 1970's by Welles Wilder. It is a momentum oscillator which measures the speed and change of price movements. RSI also determines the strength or weakness of a security. It compares the magnitude of gains to losses in a specific period of time. By using this we can identify or confirm over bought and oversold conditions in securities.
 According to Wilder's theory when the price increases very rapidly, at some point it is considered as over bought and when the price decreases, at some point it is considered over sold. At this point a reversal is possible. Wilder suggested a smoothing period of 14.
 In stock market graph RSI moves between 'zero' and 'hundred'. RSI indicator has an upline at 70, a down line at 30 and a midline at 50.Above 70 line the security or financial instrument is over bought and below thirty line it is over sold. The midline 50 shows that there is no trend.
 Wilder also described the divergence in RSI. According to him a bullish divergence happens when price makes a newer low and RSI makes higher low. A bearish divergence happens when price makes a higher high and RSI makes lower high.
 Andrew Cardwell added some new interpretations of RSI which helps us to determine the up and down trends. According to him in up trends RSI usually moving between 40 and 80 and in down trend it moves between 20 and 60. He also observed that when the trend changes in financial instruments, that is from up trend to down trend or from down trend to up trend RSI will pass through a 'range shift'.
 Cardwell also described the positive and negative reversals in the RSI. According to him Reversals are the opposite of divergence. A positive reversal happens when price correction results in a higher low and RSI results in a lower low compared to the prior correction in an uptrend . A negative reversal happens when price correction results in a lower high and RSI makes a higher high compared to the prior rally in down trend.

                          100
    RSI = 100 -  --------
                         1 + RS
    RS = Average of up closes of 'n' days / Average of down closes of 'n' days.

 An example for RSI calculation is given below

Date	Close	Change	Gain	Loss	Average Gain	Average Loss	RS	RSI (14)
01-Jul-13	120.2
02-Jul-13	125.4	5.2	5.2
03-Jul-13	124.8	-0.58		0.58
04-Jul-13	128.4	3.53	3.53
05-Jul-13	129.3	0.92	0.92
08-Jul-13	128.5	-0.82		0.82
09-Jul-13	132.5	4.05	4.05
10-Jul-13	134.2	1.7	1.7
11-Jul-13	133.3	-0.9		0.9
12-Jul-13	135	1.7	1.7
15-Jul-13	136.5	1.5	1.5
16-Jul-13	135.5	-1		1
17-Jul-13	137	1.5	1.5
18-Jul-13	135	-2		2
19-Jul-13	132.5	-2.5		2.5	1.44	0.56	2.58	72.04
22-Jul-13	131	-1.5		1.5	1.33	0.62	2.13	68.10
23-Jul-13	132	1	1		1.31	0.58	2.26	69.31
24-Jul-13	132.7	0.7	0.7		1.27	0.54	2.35	70.16
25-Jul-13	133.4	0.7	0.7		1.23	0.50	2.45	71.02
26-Jul-13	134.2	0.8	0.8		1.20	0.46	2.57	72.02
29-Jul-13	133.7	-0.5		-0.5	1.11	0.40	2.81	73.73
30-Jul-13	135	1.3	1.3		1.12	0.37	3.06	75.37
31-Jul-13	136.1	1.1	1.1		1.12	0.34	3.29	76.69
01-Aug-13	137	0.9	0.9		1.11	0.32	3.49	77.74
02-Aug-13	137.7	0.7	0.7		1.08	0.29	3.66	78.55
05-Aug-13	138.6	0.9	0.9		1.06	0.27	3.90	79.59
06-Aug-13	137	-1.6		1.6	0.99	0.37	2.69	72.88
07-Aug-13	137.5	0.5	0.5		0.95	0.34	2.79	73.63
08-Aug-13	136.3	-1.2		1.2	0.89	0.40	2.20	68.73
09-Aug-13	134.7	-1.6		1.6	0.82	0.49	1.68	62.73
12-Aug-13	135	0.3	0.3		0.78	0.45	1.73	63.38
13-Aug-13	135.9	0.9	0.9		0.79	0.42	1.88	65.32
14-Aug-13	136.5	0.6	0.6		0.78	0.39	1.99	66.59
15-Aug-13	137.8	1.3	1.3		0.82	0.36	2.25	69.22
16-Aug-13	138.5	0.7	0.7		0.81	0.34	2.40	70.56
19-Aug-13	139	0.5	0.5		0.79	0.31	2.51	71.52
20-Aug-13	138	-1		1	0.73	0.36	2.02	66.84
21-Aug-13	138.5	0.5	0.5		0.71	0.34	2.12	67.97
22-Aug-13	139.7	1.15	1.15		0.74	0.31	2.38	70.46