THE LECTURE-DEMONSTRATION AND INDIVIDUAL LABORATORY METHODS COMPARED. 111. EXPERIMENTAL The work of six sections of general college chemistry introdwed to the study by lecture demonstrations has been campxed with the work of six sections introduced by the individual laboratory method. A total of 299 students i n four colleges and taught by jive instructors has been studied. Stundard chemistry aptitude and training tests, the ordinary examinations and teaching grades have been used i n com@ring the work of the students. The effect of the difference i n the first semester's work on later work has been given some consideration. Student preference and opinion has received attation. The experimental work has been summarized; conclusions and corolhries are stated.
. . . . . .
The data used in comparing the relative merits of class demonstration and individual laboratory instruction in first-year college chemistry were furnished by twelve sections of college general chemistry students. The twelve sections were from six groups of two paired sections each. A total of 299 students in four colleges and taught by five instructors was involved. One section of each group was taught during the first part of the year, generally a semester, by class demonstration with no individual lahoratory work during this introductory work, while the paired section was taught throughout the year's work by the more commonly used individual laboratory method. After the introductory period by class demonstration, generally for one semester, this section of students joined the other section in study by the individual laboratory method. The students were paired on the basis of pre-tests, the Iowa Placement Examination, Chemistry Aptitude; a chemistry training test, Powers' General Chemistry Examination; and group intelligence tests. The attainment of the paired sections was measured on the ordinary items considered in grading chemistry students. Standard chemistry training tests, the Iowa Placement Examination, Chemistry Training, Powers' General Chemistry Test, and Rich's Chemistry Test were given a t intervals. An attempt was made to devise tests for each group that could be scored as nearly objectively as seemed reasonable. The reliability of the various tests was determined by correlating the scores on the odd-numbered questions with scores on the even-numbered questions as earned by group 5-6 students. The reliability of the whole test was calculated from that of the half test by using the Spearman-Brown formula. The mean reliability of twenty-four tests was determined by this method to be 0.74. As an indication of the validity of the tests we know that the coefficient of correlation of the sum of tests I-IX with the Iowa Placement Examination, Chemistry Training, given a t the end of the first semester, is 0.66. With the teacher's grade, as recorded in the registrar's office, the correlation is 0.68. 1277
JOURNAL OF CHEMICAL EDUCATION
1278
JULY.1932
In order to compare the groups with each other and with the norms developed by the authors of the test, Iowa Placement Examination, Chemistry Aptitude, scores for all the sections are shown in Table I. The reader should bear in mind that, except for group 7-8, this was only one of two or three measures used in pairing the students. The authors' norms for this test, based on 1140 cases, are: upper quartile score 74, median 60, lower quartile 44. In only two sections, those of group 11-12, are the mean scores on the Chemistry Aptitude test above this median; and in three sections those of group 5-6 and the laboratory section of group 1-2, the mean chemistry aptitude test scores are below the authors' lower quartile score. These data on chemistry aptitude should be. held in mind in considering all that follows. TABLE I Mean Scores Made by the Twelve Sections on the lo& Placement Examination, Chemistry Aptitude and Total Number of Students in Each Section Group
Demonstrdion Section Laboratory Section No. Demonstration Section No. Laboratory Section
1-2
3-4
5-6
7-8
9-10
11-12
45.1 43.5 27 21
46.2 45.3 17 28
42.4 41.4 19 25
49.5 49.7 23 66
51.6 49.4 17 15
65.0 67.0 22 19
In pairing the students greater weight has been given to the Iowa Placement Examination, Chemistry Aptitude, than to any other single measure. To all of the groups except group 7-8, Powers' General Chemistry Test was also given. Group intelligence test scores were also available for part of the groups. Where scores were available from the three types of tests equal weight was given to each in pairinfstudents. Where the intelligence test scores were not available double weight was given to the chemistry aptitude test scores. The chemistry training test scores from Powers' test were less significant because such a small fraction of the students had received high-school or other training in chemistry. The weighting of the predictive tests was arbitrarily made. I t did not seem expedient to wait until correlations could be made to determine the relative predictive value of the various tests for the groups involved. However, subsequent correlations have justified in the main the weighting used. The mean of ten correlations of the Iowa Placement Examination, Chemistry Aptitude, scores with attainment measures is 0.47; of two correlations of group intelligence test scores with attainment measures is 0.52; of six correlations of Powers' General Chemistry Test scores with attainment measures is 0.35; and of eight correlations of the combined predictive measures, or "expectation ranks" with attainment measures is 0.53. Comparison by Groups, Percentile Ranks One of the bases of comparison of the attainment of the demonstration sections of the various groups with the attainment of the laboratory sec-
V ~ L9,. N o . 7 DEMONSTRATION VERSUS LABORATORY. 111
1279
tions has been the percentile ranks of paired students earned on the various measures of attainment. To illustrate the pairing and the relationship of the derived percentile ranks to the raw scores, Table I1 shows the first mid-semester examination scores and the corresponding percentile ranks for the paired students of group 1-2. This is the only group made up of both men and women students in which an attempt was made in pairing to pair men only with men and women only with women. Consequently, in the tables that immediately follow, no account is taken of this division, but in a later section, comparing men and women, the division is utilized. The percentile ranks of the scores are obtained for the groups as a whole without regard to whether a score is made by a demonstration or a laboratory student. We are interested a t this time in the combined percentile scores for men and women, lower half of the group, upper half of the group;and the whole group. TABLE 11 Illustrative Data: Conversion of Raw Scores into Percentile Ranks, First Mid-Semester Examination, Group 1-2 Row scora P e l r e n i J ~Rank Lob. Dam. Lob. ufifiar war/: Man
Ucm.
91 91 91 91 95 95 71
75 86 95 95 97 81 81
Mean
57 57 57 57 80 80 16
21 44 80 80 88 32 32
57.7
53.9
Raw Scare Percadila Rank Lob. Dcm. Lab. U*pw Half: Women
Dm.
100 100 100 100 100 82 82 94
LOWW Half: Ma"
93 9'3 94 62 84 72
76 76 73 80
F3
63 40 82 88 82 Mean Mean. All Men
ti'J
63 ti9 F 42 18 1
48 38.8 47. 6
100 78 95 95 97 r 95 94 94 Mean Lower Half: Womcn
92 95 88
94 60 60
01 80 48
69 3 3
89 81
77 89
52 32 47.3
26 52 25.3
63.4
51.1
68.3
64.4
42.7
24.2
55.5
44.3
Mean Mean, All Women Mean, Upper Half Men and Women Mean, Lower Half Men and Women Mean, All Men and Women
JOURNAL OF CHEMICAL EDUCATION
1280
JULY.
1932
Thedata of Table I11 are based on this pairing of students from group 1-2. In Table I11 the data for Test I, the first of the attainment measures, should be read, "The mean percentile ranks earned by group 1-2 students are, in the upper half, demonstration, 53.8; laboratory, 48.7; in the lower half, demonstration, 45.9; laboratory, 50.8, and in the whole group, demonstration, 50.0, laboratory, 49.8." The combination of results for the first half-semester in the upper half of the sections is slightly favorable to the laboratory, in the lower half, to demonstration. For the second half-semester the combination of results TABLE 111 Mean Percentile Scores on Pre-Tests and Measures of Training of the Upper Half, Lower Half, and Whole of Demonstration and Laboratory Sections of Group 1-2 for the Rust Semester Memwe
Pm-Tsst la. C. A. Exam. Powers Exam. Group I. T. Mean Ackieument Test I I1 I11 IV Mid-Sem. Exam. Mid-Sem. Grade Test V VI VII VIII IX X la. C. T.Exam. Part I I1 I11 IV Sem. Exam. Sem. Grade 1st Half Sem. Summary 2nd Half Sem. Summary Summary by (Corrected) Measures* (Uncorrected)
u p p w Holf Dm. Lob.
Loser Half Dm. Lab.
lVh0l" Group Lob.
Dcm.
52.3 49.8 51.2 51.1
47.7 .50.2 48.8 48.9
500 48.7 46.5 42.4 56.5 54.0 56.5 62.5 57.4 53.0 53.9, 58.6 57.1 62.1 49.1 53.2 55.7 61.9
49.8 51.6 57.6 57.9 44.a 46.0 43.5 37.4 42.5 41.7 46.8 46.1 41.4 43.0 37.7 50.8 46.8 44.1 38.0
49.6
50.5
56.9 14 15
43.1 5 4
ijg.3
* Corrected and not corrected for difference in ability of the two sections.
V ~ L9,. No. 7 DEMONSTRATXON VERSUS LABORATORY. 111
1281
is distinctly favorable to demonstration in the sections as a whole and in the upper halves of the sections, and much more markedly so in the lower halves of the sections. The combination of the pre-tests, chemistry aptitude and training, and intelligence, shown a t the beginning of Table I11 indicates that the sections are quite similar throughout in ability to study chemistry. ~ c t u a lthe i ~ demonstration section is slightly better, as indicated by the mean, than the laboratory section, in the upper half by 2.0 percentiles, in the lower half and whole group by 2.2 percentiles. In such attainment measures as Part IV of the Iowa Placement Examination, Chemistry Training, in which the upper half of the demonstration section does not exceed the laboratory section as much as the pre-tests indicate should be the case, the data may be said to favor the laboratory section. If these slight differences in ability are taken into account the work of this semester may be summarized, in accordance with attainment measures as a whole, by saying that, in the upper half of the sections, the results for the individual measures favor demonstration twelve to seven, in the lower half sixteen to three, and in the whole group the measures favor demonstration fourteen to five. Table IV gives a general summary of percentile rank results for all groups. As is shown in this table the various groups do not show uniform results. When all the measures of all the groups are summarized by semesters no marked differences are seen in the upper halves of the groups, but in the lower halves and in the whole group the demonstration sections are favored during both semesters. The difference favoring the demonstration sections is more marked in the second semesty than during the first semester. This same variation of results between the upper and lower halves of the groups exists if we summarize by groups instead of by separate measures within the groups.
Comparison by Pairs One of the simplest methods of comparing the results of the two methods of instruction is that of counting the pairs of students furnishing data favorable either to the demonstration or the individual laboratory method. The same pairing that was used in the preceding tables has furnished the data of this section. From the data in Table I1 of the preceding section, by actual count, i t may be seen that for group 1-2 on the midsemester examination, of the upper group men, three pairs furnished data favorable to the demonstration method and four pairs furnished data favorable to the individual laboratory method. In the other sub-divisions of this group the corresponding ratios of demonstration to laboratory are: lower-half men, six to two; upper-half women, four to two; lower-half women, four to two. Among the upperhalf women there are two pairs and among the lower-half women one pair
JOURNAL OF CHEMICAL EDUCATION
1282
JULY, 1932
TABLE IV General Summary of Percentile Rank Results for All Groups VPPcr Ifalf
G,ou*r
1-2 1st Semester 2nd Semester 3 4 1st Semester 2nd Semester 5-6 1st Semester 2nd Semester 7-8 1st Semester 2nd Semester 9-10 1st Quarter 2nd Quarter 11-12 1st Semester 2nd Semester Summary by Measures Total 1st Semester Total 2nd Semester Both Semesters Per Cent. 1st Semester 2nd Semester Both Semesters Summary by Groups 1st Semester 2nd Semester Both Semesters Per Cent. 1st Semester 2nd Semester Both Semesters
Lower
Holf Lob.
Whole Gvoup Dm" Lob.
DE".
Lob.
Dlrn.
12 8
7 3
16 10
3 1
14 10
5 1
12 1
6 11
13 7
5
5
16 2
2 10
8 3
13 10
14 12
7 1
12 10
9 3
13 6
5 2
15 3
3
5
16 4
2 4
1 Li
5 1
2 5
4 2
2 5
4 2
7 0
10 2
7 2
10 0
7 1
10 1
53 24 77
46 29 75
67 39 106
32 14 46
67 32 99
32 21 53
45.3 50.6
54.9 49.4
73.6 +69.8
36.4 30.2
60.3 65.1
39.7 34.9
3 3 6
3 3 6
4 5 9
50.0 50.0 50.0
50.0 50.0 50.0
66.7 S3.3 75.0
2 1 3 33.3 16.7 25.0
4 3 7 66.7 75.0 70.0
2 1 3 33.3 25.0 30.0
with no difference between the scores. Such pairs are not counted as favorable either to demonstration or individual laboratory. These data may be combined in various ways and in the tables that follow the following types of combinations are used: all upper-half students, seven favorable to demonstration, six favorable to individual laboratory; lower-half, ten to four; and whole group, seventeen to ten. Table V gives the percentage of pairs of students in the upper half, lower half, and whole groups furnishing data favorable to demonstration or laboratory on the various term and semester non-standard examinations. The summary of this table shows that, in the upper half of these groups,
V ~ L9,. No. 7 DEMONSTRATION VERSUS LABORATORY. 111
1283
nine of these examinations furnish data favorable to demonstration to five favorable to laboratory. In the lower half of the group the corresponding ratio is thirteen to one, and in the groups as a whole, eleven to three. These non-standard examinations are probably more nearly valid than the standard examinations, since they are designed particularly for the group to which they are given, and to cover the subject matter taught. TABLE V Percentage of Pairs Furnishing Data Favorable to Demonstration or Laboratory on Ron-Standard Examinations in the Upper Half, Lower Half, and Whole Groups Groups
1-2 1st Mid-Sem. 1st Sem. 2nd Sem.
U m n Half Lab.
Dm.
Lovlcr Half Dem. Lob.
Whole Group Lo&.
Den.
53.9 73.3 70.0
46.1 26.7 30.0
71.4 81.8 75.0
28.6 18.2 25.0
. 76.9 72.7
37.0 23.1 27.3
77.8 100.0 33.3
22.2 0.0 66.7
63.6 100.0 70.0
36.4 0.0 30.0
70.0 100.0 52.7
30.0 0.0 47.3
30.0
70.0
60.0
40.0
45.0
55.0
37.5 46.7 69.2 72.7 81.8 40.0
62.5 53.3 30.8 27.3 18.2 60.0
78.6 57.2 53.9 .77.8 58.3 55.59
21.4 42.8 46.1 22.2 41.7 44.5
56.7 51.7 61.5 76.0 69.6 47.3
43.3 48.3 38.5 25.0 30.4 52.7
57.2 9
42.8 5
20.0 13
80.0 1
40.0 11
60.0 3
63.0
3-4
1st Mid-Sem. 1st Sem. 2nd Sem. 5-6 2nd Sem. 7-8 1st Month 2nd Month 3rd Month 4th Month 1st Sem. 2nd Sem. 11-12 1st Sem. Summary by Measures
Table VI gives the percentage of the pairs furnishing data favorable to demonstration or laboratory on the various standard examinations. The ratios summarized are: in the upper hali, six favorable to demonstration to eleven favorable to the individual laboratory method; in the lower half, ten for demonstration to seven for laboratory; and in the whole of the groups, ten to six. No attempt is made to account for the difference between these results and those for the non-standard examinations. It has been pointed out, however, that the standard examinations do not cover the subject matter studied as closely and as exclusively as do the nonstandard examinations. Table VII gives the percentage of the pairs furnishing data favorable to demonstration or laboratory on letter grades a t the term and semester intervals indicated. It is interesting to note that all of the differences between the sections of group 3 4 a t the mid-semester and semester intervals
1284
JOURNAL OF CHEMICAL EDUCATION
JULY.1932
were favorable to the demonstration method. This condition was partly reversed a t the end of the second semester, when eighty per cent. of the differences in the upper group favored the individual laboratory method. The data are summarized: The demonstration method is favored throughout in the upper half, eleven to four; in the lower half, fourteen to two; in the whole of the groups, twelve to three. Grades in chemistry may be depended on more than in some subjects since it is possible to use more objective data in making the grade. TABLE VI Percentage of Pairs Furnishing Data Favorable to Demonstration or Laboratory on Standard Objective Examinations in the Upper Half, Lower Half, and Whole Groups Gmups
UPPn Holf ~m,. ~ o b .
Lower Holf
D
~
~
~. a
.
Whole Group D ~ ~ h. b .
1-2 la. C. T. Exam. Rich, 2nd Mid-Sem Powers
3-4 Ia. C. T. Exam. Rich, 2nd Mid-Sem. Powers 5-6
Rich, 1st Mid-Sem. Ia. C. T. Exam. Columbia Rich, 2nd Mid-Sem. Powers 7-8 la. C. T. Exam.
Powen 9-10 Rich, 1st Mid-Qua. la. C. T. Exam., 2nd Mid-Quar. 11-12 Rich, 1st Mid-Sem. Ia. C. T. Exam. Columbia Summary by Measures
Table VIII is a summary table showing the percentage of pairs, upperhalf, lower-half, and whole groups furnishing data favorable to demonstration or laboratory on all measures combined by simple addition. When summarized in this manner as much of the data favors one method as the other in the upper halves of the groups. However, in the lower half the demonstration method is favored by a ratio of thirteen to four and in the whole group by a ratio of twelve to five.
VOL.9, NO. 7 DEMONSTRATION VERSUS LABORATORY. I11
1285
TABLE VII Percentage of Pairs Furnishing Data Favorable to Demonstration or Laboratory on the Term Grades, in the Upper Half, Lower Half, and Whole Groups
unocr ~ a l f Grou*r
1-2 1st Mid'Sem. 1st Sem. 2nd Sem. 3-4 1st Mid-Sem. 1st Sem. 2nd Sem. 5-6 1st Mid-Sem. 1st Sem. 2nd Sem. 7-8 1st Month 2nd Month 3rd Month 1st Sem. 2nd Sem. 9-10 1st Quarter 2nd Quarter 11-12 1st Sem. 2nd Sem. Summary by Measures
Lowa I f d f
Whole Croun Dam. Lab.
Dam.
Lob.
Dcm.
Lob.
50.0 80.0 85.7
50.0 20.0 14.3
0.5 100.0 58.3
38.5 0.0 41.7
56.5 88.9 68.5
43.5 11.1 31.6
100.0 1000 20.0
0.0 0:0 80.0
100.0 100.0 57.2
0.0 0.0 42.8
100.0 100.0 41.7
0.0 0.0 58.3
ti04 50.0 16.7
40.0 50.0 83.3
66.7 50.0 83.3
33.3 50.0 16.7
65.0 50.0 50.0
35.0 50.0 50.0
54.6 62.5 71.4 66.7 50.0
45.4 37.5 28.6 33.3 50.0
85.7 46.2 60.0 66.7 50.0
14.3 53.8 40.0 33.3 50.0
72.0 52.4 66.7 66.7 50.0
28.0 47.6 33.3 33.3 50.0
42.8 75.0
57.2 25.0
66.7 83.3
33.3 16.7
56.2 78.6
43.8 21.4
GOO 0.0
40.0 100.0 4
20.0 '66.7
80.0 33.3
40.0 36.4 12
60.0 63.6 3
11
14
(
2
Comparison of Groups in Relation to Predicted or Expectation Ranks of Individuals One of the first methods used by the writer for comparing the work of the demonstration sections with that of the laboratory sections was intended to include all of the students in each section. For example, forty-four group 5-6 students, twenty-five in the demonstration section and nineteen in the laboratory section; and thirty-eight group 11-12 students, twenty-one in the demonstration section and seventeen in the laboratory section, were ranked on the Iowa Placement Examination, Chemistry Training, on Powers' General Chemistry Examination and, in addition, when the data were available on a college classification or group intelligence test. The rank of one was given for the best score. The group 5-6 students were given the ranks one to forty-four; the group 11-12 students the ranks one to thirty-eight. These ranks were combined into composite ranks referred to as "expectation ranks." The earned ranks on the various attainment measures vgere compared with the corresponding expeclatiun ranks.
JOURNAL OF CHEMICAL EDUCATION
1286
JULY.
1932
TABLE VIII Percentage of Pairs Furnishing Data Favorable to Demonstration or Laboratory on All Measures Combined in the Upper Half, Lower Half, and Whole Groups Dem.
Whair Group Lab.
Lower Half Ucm. Lob.
U m c r IInlf
tir:rouos
Lob.
Uem.
1-2 1st Half. 1st Sem 2nd Half, 1st Sem. 2nd Semester 3 4 1st Half, 1st Sem. 2nd Half, 1st Sem. 2nd Semester &6 1st Half, 1st Sem 2nd Half, 1st Sem. 2nd Semester 7-8 1st Half, 1st Sem. 2nd Half, 1st Sem. 2nd Semester
%lo 1st Quarter 2nd Quarter .. 11-12 1st Half, 1st Sem 2nd Half, 1st Scm. 2nd Semester Summary by Measures
Table IX summarizes the work of the six groups as percentages of students who excelled their expectation ranks on first semester grades, second semester grades, the Iowa Placement Examination, Chemistry Aptitude, given at the close of the first semester and Powers' General Chemistry Test given a t the close of the second semester. For each of the four measures, TABLE
M
Summary: Percentage of Students Who Exceed Their Expectation Rank NO.of C. T. Irr Sem. rawerr' 2nd scmcstrr .SI#cdrnls
Ouub
Dam.
Lnb.
1-2 25 18 13 27 3-4 25 5-6 19 16 46 7-8 9-10 15 15 20 16 11-12 Summary by Groups
-
* Experimental
Dram. Lab.
Dcm
64 50 47 56 57 38 4
28 33 5fi 48 47 44
2
Crode Lab.
Dem.
GO 62 53 69 40 40 4
22 33 40 42 53 56 2
Edition. Columbia Chemistly Test.
Erom. Dem. Lob.
64 31 67 60 56 58* 4
33 37 35 49 57 42* 2
Grodc
Dcm.
Lob.
56 38 44 60 64 50
33 48 50 46
4
47 33 2
VOL.9, NO.7 DEMONSTRATION VERSUS LABORATORY. I11
1287
four of the six groups furnish data favorable to the individual laboratory method. Groups 1-2 and 7-8 are entirely favorable to the demonstration method. The other four groups furnish two measures favorable to the demonstration method and two measures favorable to the individual laboratory method, though the measures are not grouped by diierences identically for the four groups.
The Work of Men and Women Compared As it was pointed out in the section using the percentile rank method of comparison, men were paired only with men and women with women in group 1-2. This pairing has made it possible to use the same data to compare men with men, women with women, and men with women. Since five of the groups are made up of men and women while the sixth, group 11-12, made up of men only, furnishes data most favorable to the individual laboratory method, the question may well be raised concerning the relative effectiveness of the demonstration and laboratory methods for men as compared with women. TABLE X Summary: Work of Men and Women of Group 1-2 by Percentile Ranks for Each Half-Semester GlowPr
Men 1st Mid-Semester 2nd Half-Semester 1st Half 2nd Semester 2nd Half 2nd Semester Women 1st Mid-Semester 2nd Half-Semester 1st Half 2nd Semester 2nd Half 2nd Semester
Umer Half Dc*. Lab.
Dm.
Lab.
60.3 66.8 56.8 67.3
46.1 54.4 64.4 55.2
39.5 26.5 50.6 30.3
52.0 61.0 60.3 61.8
48.1 40.8 54.1 41.4
34.3 43.6 33.1 34.9
36.4 32.8 30.3 29.3
47.7 52.7 43.1 52.0
53.0 44.9 41.2 44.7
58.6 58.1 53.2 68.6
58.2 57.4 57.1 51.0 66.5 52.9 51.8 59.9
Lawn Half
.
Z
Whale Croup Den. Lab.
Table X shows the summary of the work of the men and women of group 1-2 for each half-semester for the year. In only four of twenty-four comparisons do the laboratory section students exceed the record of the demonstration section students. These are the upper-half laboratory men for the first half of the second semester and the upper-half and lower-half and whole-group laboratory women for the first half of the first semester. In eleven of the twelve divisions of this table, there are indications that the women have used the laboratory method relatively better than the men. This is true in spite of the fact that the pre-tests indicate that the demonstration women have more ability to study chemistry than do the laboratory women. To illustrate the difference cited we note that for the second half of the first semester in the upper half of the group, the demonstration method is favored among the men by 9.4 percentiles, while the
1288
JOURNAL O F CHEMICAL EDUCATION
JULY,
1932
demonstration method is favored among the women only by 5.2 percentiles. Table X I shows the percentage of the measures of attainment favorable to the demonstration or individual laboratory method, for men and women, first and second semester, and upper half, lower half, and whole group. In every comparable division the data are less unfavorable to the individual laboratory method among the women than among the men. TABLE XI Summary by Pairing. Percentage of Measures Favorable to Demonstration or Laboratory. Men and Women of Group 1-2 Upper Half
I+'hoIr Group Dem. Lab.
GrouP.5
Dem.
Loh.
Lorun H o l l Dem. Lob.
Men 1st Semester 2nd Semester
iR 92
25 8
87 100
1P 0
83
11
inn
0
69 80
31 20
71 67
29 33
72 07
28 33
Women
1st Semester 2nd Semester
Table XI1 summarizes the predictive tests and the attainment tests as mean sigma scores for the six groups of students. In estimating whether results are favorable to the individual laboratory method or to the demonstration method, differences in the mean sigma scores of the predictive tests for the sections are taken into account. For example, the mean difference on the attainment tests favking the demonstration men of group 1-2 is 0.69 sigma, but the predictive tests show that the demonstration men should have been 0.02 sigma better, hence these data are said to favor the demonstration method to the extent of 0.67 sigma. The mean sigma attainment results favor the group 1-2 laboratory women by 0.06 sigma. The predictive tests indicate, however, that these laboratory women should have been better by 0.12 sigma, hence the data are said to favor the demonstration women by 0.06 sigma. Among the men, the data favor the demonstration method in four groups and the individual laboratory method by 0.01 sigma only in one group. Among the women, the data favor the demonstration method in four groups and the individual laboratory method in one group. Taking all the groups as a unit the demonstration method is favored by the data from the men by 0.41 sigma, women by 0.25 sigma, and both combined by 0.31 sigma. These data again indicate that the men have not used the laboratory relatively to as good an advantage as have the women. An idea of the statistical significance of the difference between the achievement of the demonstration and laboratory sections of the groups may be gained by a study of Table XIII. The method here used is es-
VOL. 9. No. 7 DEMONSTRATION VERSUS LABORATORY.
111
1289
TABLE XI1 Mean Sigma Scores of Pre-Tests and Attainment Tests for Six Groups Mcn Group and Ted
Den.
Lob.
0.06 0.26 0.67
0.04 -0.43
P. T. A. T. Difference*
-0.33 0.04 0.80
0.06 -0.47
A. T. Difference*
-0.28 -0.27 0.00
0.24 0.25 0.00
A. T. Difference*
-0.07 0.09 0.61
0.41 -0.04
A. T. Difference*
0.05 0.22 0.41
1-2
Difference' 3-4
-0.20 -0.44
11-12
P. T.
-0.10 -0.13
A. T. Difference* Mean Difference*
0.18 0.16 0.01
0.41
* Difference between Sigma Scores on AttainmentS~estsof Demonstration and Laboratory Sections, allowing for difference in Sigma Scores on Pre-Tests. The difference is recorded under the section which is favored. sentially the "critical ratio" method discussed by McGaughy ( 1 ) . He defines the critical ratio as the ratio of a difference of averages to its prohable error. A critical ratio of three is considered statistically significant. McGaughy used the so-called short formula for the probable error of a differenceof averages. This formula adapted to the differenceof the averages of the demonstration and the laboratory section results would read: P. E. (Diff. of Av.'s of D & L) = 0.6745
d'
? +
No
NL
Walker (Z), however, has pointed out that, in cases where a correlation exists between the variates, the longer formula is necessary. The longer formula adapted for use in this study reads: P. E. (Diff. of Av.'s of D & L)
=
0.6745
S. D.3. S. D.D X S. D.L - 2rrn. NL ~NDNL
1200
JOURNAL OF CHEMICAL EDUCATION
J a y . 1032
TABLE XIII Critical Ratios between Demonstration and Laboratory Section First and Second Semester Grades and Iowa Placement Examination, Chemistry Training Scores GIWP Numbcr
1-2 19 Dem. 18 Lab. 3 4 12 Dem. 22 Lab. 5-G 17 Dem. 18 Lab. 7-8 14 Dem. 33 Lab. ll-10 15 Dem. 15 Lab. 11-12 10 Dem. 14 Lab.
Mcosvrc
1st Sem. Grade 2nd Sem. Grade Ia. C. T. Exam. 1st Sem. Grade 2nd Sem. Grade la. C. T. Exam. 1st Sem. Grade 2nd Sem. Grade Ia. C. T. Exam. 1st Sem. Grade 2nd Sem. Grade la. C. T. Exam. 1st Q u a . Grade 2nd Q u a . Grade Ia. C. T . Exam. 1st Sem. Grade 2nd Sem. Grade la. C. T. Exam.
Sigma Dlffirencr*
Pawing
Crilicnl Ralio Pormulo Sho11 Long
0.70 0.53 0.47 0.49 0.24 0.20 0 . 16 0.51 0.17 0.45 0.40 0.31 0.10 0.43 0.13 0.32 0.10 0.05
Dem. Dem. Dem. Dem. Lab. Dem. Dem. Dem. Lab. Dem. Dem. Dem. Dem. Dem. Dem. Lab. Dem. Dem.
4.20 2.17 2.23 1.47 1.00 1.39 0.68 2.03 0.70 1.74 1.78 1.32 0.64 1.89 0.46 1.22 0.32 0.24
7.7!) 3.08 3.31 2.01 1.94 2.52 1.30 3.42 1.44 2.85 2.80 2.21 1.23 3.08 0.65 2.33 0.57 0.47
* T h e difference here shown takes into account the difference in aptitude of the sections compared, as measured by the pre-tests.
Since the writer desired to calculate the critical ratios for typical data from the equated sections of the six grou&, in which the individuals were not paired, coefficients of correlation could not be obtained in the usual manner. The suggestion of Walker, that the coefficient of reliability of the tests used be substituted for "r" has been followed. As pointed out earlier, the mean cwfficient of reliability of twenty-three typical tests used is 0.735. Three summary measures were made the basis of the calculation of the critical ratios, first-semester grades, the Iowa Placement Examination, Chemistry Training, given a t the close of the first semester, and the secondsemester grades. The actual difference between the averages obtained by the demonstration and laboratory sections is corrected according to the difference in the predictive test means of the sections. For example, the predictive test mean for group 1-2 indicates that the laboratory section should be better by a difference of 0.11 sigma. Actually the demonstration section attained better records on the three measures and the actual differencesare increased by the value corresponding to 0.11 sigma. On the other band, the predictive test mean indicates that the demonstraticn section of group 3 4 is superior to the extent of 0.06 sigma. Such differ-
VOL.9, No. 7 DEMONSTRATION VERSUS LABOFUTORY. 111
1291
ences in indicated ability for all groups are combined with actual attainment differences to give the values of Table XIII. By use of the short formula only one critical ratio greater than three is obtained. This is a critical ratio of 4.20 between the first semester grades of the demonstration and laboratory sections of group 1-2 and is favorable to the demonstration section. By the longer formula five critical ratios above three and two more only slightly less are obtained, all favorable to the work of the demonstration sections. Only three of the eighteen measures favor the work of the laboratory sections. The largest critical ratio favorable to any laboratory section is.2.33 resulting from the first semester grades of the group 11-12 students. It will be recalled that this group was distinctly the most capable as measured by the Iowa Placement Examination, Chemistry Aptitude. From groups 1-2, 3 4 , and 5-6 eleven demonstration-section students have made twenty-three, and twenty-one laboratory-section students have made sixty-eight upper-class semester grades in chemistry, all under one instructor. The mean grade for the demonstration sections is -0.14 sigma, and for the laboratory sections is 0.05 sigma. This indicates that the work of the demonstration section students is inferior, but in comparison with their Iowa Placement Examination, Chemistry Aptitude, scores indicates that their work is relatively superior. The aptitude score for the demonstration section is -0.37 sigma, and for the laboratory section is 0.17 sigma. This means that the sigma index for the demonstration students has improved 0.23 while that of the laboratory students has shown a loss of 0.12. I)' Student Preference and Opinion If we are to adopt a student-centered philosophy of education, we may well consider the opinions and preferences of the students. Table XIV shows the preference of men and women students from groups 1-2, 3-4, and 5-6 for laboratory or demonstration as a method for beginning the course in general chemistry. These opinions were expressed at the middle of the second semester after the demonstration section had worked for one half-semester by the individual laboratory method. Of all the students beginning the course by the individual laboratory method, 68.6 per cent would prefer that method if they were beginning the course again. The choice of 77.1 per cent. of all the students beginning the course by the lecture demonstration is that same method. The choice of the men who began by the individual laboratory method for that method is more pronounced than is that of the men who began by the demonstration method for that method. On the other hand, the choice of the women who began by the individual laboratory method for that method is not as pronounced as is the choice of those who began by the demonstration method for that method.
1292
JOURNAL OF CHEMICAL EDUCATION
JULY.1932
TABLE XIV The Preference of Men and Women Students from Groups 1-2.34.56 for Laboratorv . . m Demonstration Work Mcn from Lob. Who P~efcr Lab. Dm.
Glou9r
Men fro", Dam. Who Prefer Dam. Lob.
1-2 3 4 5-6 Combined Percentage
5 2 2 9 31.0
G,O"~S
1-2 3 4 56 Combined Percentage Men and Women Percentage
womr,, from Lob. who Pwfcl Lab. Dcm.
8 12 4 24 63.2 48 68.6
2 6 6 14 36.8 22 31.4
8 5 7 20 69.0
Womrn from Dim. Who P.lf
