Predicting Monthly Car Sales: The Residuals are the Story

I'll produce predictions for US car sales by manufacture every month. There are already several blogs that describe the industry and sales that do a great job. Autoblog by the Numbers and Counting Cars are some to mention. 

Unlike their analysis, I'll try to focus on the residuals (the stuff I can't predict) to tell the story. To highlight the difference, I think its instructive to look at what Autoblog mentioned.

The Autoblog article (link above) highlights Mitsubishi for increasing sales. However, my prediction for Mitsubishi sales are pretty much exactly what the sales were. In essence, given this model, we didn't learn much. On the other hand, Land Rover and Jaguar had the largest residuals (in percent terms) and Land Rover and Acura had the largest deviance (Residual / Variance). I think these results are more telling because we didn't predict them correctly; something might have changed. 

I'll publish this on a new blog: datAmotive.

Github

Here is a  Shiny App For Car Sales and below are graphs / tables of my current analysis and future predictions. 

	Predicted Values 9/14	Actual Values 9/14	log(Predicted/Actual)	Deviance
Acura	488.036	576.333	0.166	1.731
Audi	632.252	621.542	-0.017	0.326
BMW	1,061.329	1,066.083	0.004	0.032
Buick	649.648	727.750	0.114	0.571
Cadillac	568.021	576.208	0.014	0.089
Chevrolet	6,284.594	6,411.375	0.020	0.135
Chrysler	1,058.392	1,199.208	0.125	0.710
Dodge	1,892.465	1,834.167	-0.031	0.172
Ford	7,374.669	7,177.542	-0.027	0.285
GMC	1,602.260	1,594.542	-0.005	0.029
Honda	4,434.780	4,349.625	-0.019	0.174
Hyundai	2,291.306	2,333.750	0.018	0.271
Infiniti	315.217	326.542	0.035	0.234
Jaguar	37.834	47.583	0.229	0.908
Jeep	2,491.378	2,301.292	-0.079	0.853
Kia	1,853.734	1,692.833	-0.091	1.115
Land.Rover	159.975	129.417	-0.212	1.816
Lexus	1,011.967	910.500	-0.106	1.189
Lincoln	285.903	302.375	0.056	0.394
Mazda	1,074.272	999.167	-0.072	0.743
Mercedes.Benz	1,186.220	1,230.125	0.036	0.364
Mini	196.975	175.792	-0.114	0.626
Mitsubishi	231.582	231.583	0.00000	0.00002
Nissan	4,176.995	3,963.250	-0.053	0.516
Porsche	156.496	150.292	-0.040	0.408
Subaru	1,727.597	1,729.875	0.001	0.026
Toyota	6,928.472	6,059.458	-0.134	1.309
Volkswagen	1,123.412	1,083.167	-0.036	0.407
Volvo	161.531	194.458	0.186	1.070

	Predicted Values for 10/14
Acura	521.878
Audi	590.125
BMW	1,051.492
Buick	666.165
Cadillac	533.468
Chevrolet	5,693.145
Chrysler	1,097.288
Dodge	1,493.426
Ford	6,694.012
GMC	1,572.525
Honda	4,049.582
Hyundai	1,998.896
Infiniti	262.475
Jaguar	40.422
Jeep	2,132.652
Kia	1,650.236
Land.Rover	160.884
Lexus	944.946
Lincoln	272.964
Mazda	894.234
Mercedes.Benz	1,184.991
Mini	183.743
Mitsubishi	193.982
Nissan	3,629.955
Porsche	158.540
Subaru	1,694.661
Toyota	5,895.316
Volkswagen	923.242
Volvo	153.691