In 1958, the Murphy brothers established a furniture store in downtown Dallas. Over the years, they were quite successful and extended their retail coverage throughout the West and Midwest. By 1996, their chain of furniture stores had become well established in 36 states. Julie Murphy, the daughter of one of the founders, had recently joined the firm. She collected monthly sales data for 1986-1988. Data are shown in Table 3.
Use Minitab to obtain the ACF graph with 30 lags. Does the ACF graph show any seasonality?
a. No, because none of the autocorrelations at seasonal lags are significant or relatively larger than others.
b. No, we cannot tell.
c. Yes, because the first 5 autocorrelations are significant.
d. Yes, because autocorrelation at lag 12 is significant and autocorrelation at lag 24 is relatively larger.
Year Month
1986 Jan.
1986 Feb.
1986 Mar.
1986 Apr.
1986 May
1986 Jun.
1986 Jul.
1986 Aug.
1986 Sep.
1986 Oct.
1986 Nov.
1986 Dec.
1987 Jan.
1987 Feb.
1987 Mar.
1987 Apr.
1987 May
1987 Jun.
1987 Jul.
1987 Aug.
1987 Sep
1987 Oct.
1987 Nov.
1987 Dec.
1988 Jan.
1988 Feb.
1988 Mar.
1988 Apr.
1988 May
1988 Jun.
1988 Jul.
1988 Aug.
1988 Sep.
1988 Oct.
1988 Nov.
1988 Dec.
Sales
105.6
99.7
114.2
115.7
125.4
120.4
120.7
124.1
124.4
123.8
121.4
152.1
106.4
105.8
120.4
125.4
129.1
129
129.3
131.5
124.5
128.3
126.9
157.2
113.6
115
131.6
130.9
136
137.5
134.1
138.7
131.9
133.8
140.2
171